Article

Neuronal responses to static texture patterns in area V1 of the alert macaque monkey

May 1992
Journal of Neurophysiology 67(4):961-80

May 1992
67(4):961-80

DOI:10.1152/jn.1992.67.4.961

Source
PubMed

Authors:

1. We recorded responses from neurons in area V1 of the alert macaque monkey to textured patterns modeled after stimuli used in psychophysical experiments of pop-out. Neuronal responses to a single oriented line segment placed within a cell's classical receptive field (CRF) were compared with responses in which the center element was surrounded by rings of elements placed entirely outside the CRF. The orientations of the surround elements either matched the center element, were orthogonal to it, or were random. 2. The addition of the textured surround tended to suppress the response to the center element by an average of 34%. Overall, almost 80% of the 122 cells analyzed in detail were significantly suppressed by at least one of the texture surrounds. 3. Cells tended to respond more strongly to a stimulus in which there was a contrast in orientation between the center and surround than to a stimulus lacking such contrast. The average difference was 9% of the response to the optimally oriented center element alone. For the 32% of the cells showing a statistically significant orientation contrast effect, the average difference was 28%. 4. Both the general suppression and orientation contrast effects originated from surround regions at the ends of the center bar as well as regions along the sides of the center bar. 5. The amount of suppression induced by the texture surround decreased as the density of the texture elements decreased. 6. Both the general suppression and the orientation contrast effects appeared early in the population response to the stimuli. The general suppression effect took approximately 7 ms to develop, whereas the orientation contrast effect took 18-20 ms to develop. 7. These results are consistent with a possible functional role of V1 cells in the mediation of perceptual pop-out and in the segregation of texture borders. Possible anatomic substrates of the effects are discussed.

Pattern completion and disruption characterize contextual modulation in the visual cortex

Preprint

Full-text available

Mar 2023

A key role of sensory processing is integrating information across space. Neuronal responses in the visual system are influenced by both local features in the receptive field center and contextual information from the surround. While center-surround interactions have been extensively studied using simple stimuli like gratings, investigating these interactions with more complex, ecologically-relevant stimuli is challenging due to the high dimensionality of the stimulus space. We used large-scale neuronal recordings in mouse primary visual cortex to train convolutional neural network (CNN) models that accurately predicted center-surround interactions for natural stimuli. These models enabled us to synthesize surround stimuli that strongly suppressed or enhanced neuronal responses to the optimal center stimulus, as confirmed by in vivo experiments. In contrast to the common notion that congruent center and surround stimuli are suppressive, we found that excitatory surrounds appeared to complete spatial patterns in the center, while inhibitory surrounds disrupted them. We quantified this effect by demonstrating that CNN-optimized excitatory surround images have strong similarity in neuronal response space with surround images generated by extrapolating the statistical properties of the center, and with patches of natural scenes, which are known to exhibit high spatial correlations. Our findings cannot be explained by theories like redundancy reduction or predictive coding previously linked to contextual modulation in visual cortex. Instead, we demonstrated that a hierarchical probabilistic model incorporating Bayesian inference, and modulating neuronal responses based on prior knowledge of natural scene statistics, can explain our empirical results. We replicated these center-surround effects in the multi-area functional connectomics MICrONS dataset using natural movies as visual stimuli, which opens the way towards understanding circuit level mechanism, such as the contributions of lateral and feedback recurrent connections. Our data-driven modeling approach provides a new understanding of the role of contextual interactions in sensory processing and can be adapted across brain areas, sensory modalities, and species.

Inversion of pop-out for a distracting feature dimension in monkey visual cortex

Article

Full-text available

Feb 2023
P NATL ACAD SCI USA

During visual search, it is important to reduce the interference of distracting objects in the scene. The neuronal responses elicited by the search target stimulus are typically enhanced. However, it is equally important to suppress the representations of distracting stimuli, especially if they are salient and capture attention. We trained monkeys to make an eye movement to a unique "pop-out" shape stimulus among an array of distracting stimuli. One of these distractors had a salient color that varied across trials and differed from the color of the other stimuli, causing it to also pop-out. The monkeys were able to select the pop-out shape target with high accuracy and actively avoided the pop-out color distractor. This behavioral pattern was reflected in the activity of neurons in area V4. Responses to the shape targets were enhanced, while the activity evoked by the pop-out color distractor was only briefly enhanced, directly followed by a sustained period of pronounced suppression. These behavioral and neuronal results demonstrate a cortical selection mechanism that rapidly inverts a pop-out signal to "pop-in" for an entire feature dimension thereby facilitating goal-directed visual search in the presence of salient distractors.

Contextual drive of neuronal responses in mouse V1 in the absence of feedforward input

Article

Full-text available

Jan 2023

Neurons in the primary visual cortex (V1) respond to stimuli in their receptive field (RF), which is defined by the feedforward input from the retina. However, V1 neurons are also sensitive to contextual information outside their RF, even if the RF itself is unstimulated. Here, we examined the cortical circuits for V1 contextual responses to gray disks superimposed on different backgrounds. Contextual responses began late and were strongest in the feedback-recipient layers of V1. They differed between the three main classes of inhibitory neurons, with particularly strong contextual drive of VIP neurons, indicating a contribution of disinhibitory circuits to contextual drive. Contextual drive was strongest when the gray disk was perceived as figure, occluding its background, rather than a hole. Our results link contextual drive in V1 to perceptual organization and provide previously unknown insight into how recurrent processing shapes the response of sensory neurons to facilitate figure perception.

Surround Modulation Properties of Tectal Neurons in Pigeons Characterized by Moving and Flashed Stimuli

Article

Full-text available

Feb 2022

Surround modulation has been abundantly studied in several mammalian brain areas, including the primary visual cortex, lateral geniculate nucleus, and superior colliculus (SC), but systematic analysis is lacking in the avian optic tectum (OT, homologous to mammal SC). Here, multiunits were recorded from pigeon (Columba livia) OT, and responses to different sizes of moving, flashed squares, and bars were compared. The statistical results showed that most tectal neurons presented suppressed responses to larger stimuli in both moving and flashed paradigms, and suppression induced by flashed squares was comparable with moving ones when the stimuli center crossed the near classical receptive field (CRF) center, which corresponded to the full surrounding condition. Correspondingly, the suppression grew weaker when the stimuli center moved across the CRF border, equivalent to partially surrounding conditions. Similarly, suppression induced by full surrounding flashed squares was more intense than by partially surrounding flashed bars. These results suggest that inhibitions performed on tectal neurons appear to be full surrounding rather than locally lateral. This study enriches the understanding of surround modulation properties of avian tectum neurons and provides possible hypotheses about the arrangement of inhibitions from other nuclei, both of which are important for clarifying the mechanism of target detection against clutter background performed by avians.

Surround Modulation Properties of Tectal Neurons in Pigeon Characterized by Moving and Flashed Stimuli

Preprint

Full-text available

Dec 2021

Surround modulation is a phenomenon whereby costimulation of the extra-classical receptive field and classical receptive field would modulate the visual responses induced individually by classical receptive field. However, there lacks systematic study about surround modulation properties existing in avian optic tectum. In this study, neuronal activities are recorded from pigeon optic tectum, and the responses to moving and flashed squares and bars of different sizes are compared. The statistical results showed that most tectal neurons presented surround suppression as stimuli size grew larger both in moving and flashed paradigms, and the suppression degree induced by larger flashed square was comparable with that by moving one when it crossed near the cell’s RF center, which corresponds to fully surrounding condition. The suppression degree grew weaker when the stimuli move across the RF border, which corresponds to partially surrounding condition. Meanwhile, the fully surround suppression induced by flashed square was also more intense than partially surrounded by flashed bars. The results provide new insight for understanding the spatial arrangement of lateral inhibitions from feedback or feedforward streams, which would help to make clear the generation mechanism of surround modulation found in avian optic tectum.

Dependence of Contextual Modulation in Macaque V1 on Interlaminar Signal Flow

Preprint

Apr 2024

In visual cortex, neural correlates of subjective perception can be generated by modulation of activity from beyond the classical receptive field (CRF). In macaque V1, activity generated by nonclassical receptive field (nCRF) stimulation involves different intracortical circuitry than activity generated by CRF stimulation, suggesting that interactions between neurons across V1 layers differ under CRF and nCRF stimulus conditions. We measured border ownership modulation within large populations of V1 neurons. We found that neurons in single columns preferred the same side of objects located outside of the CRF. In addition, we found that interactions between pairs of neurons situated across feedback/horizontal and input layers differed between CRF and nCRF stimulation. Furthermore, the magnitude of border ownership modulation was predicted by greater information flow from feedback/horizontal to input layers. These results demonstrate that the flow of signals between layers covaries with the degree to which neurons integrate information from beyond the CRF.

Feedback neural computation in collision perception: Towards diverse selectivity

Preprint

Jan 2024

Significant strides have been achieved in the biological exploration of the locust's lobula giant movement detector (LGMD), contributing substantially to the development of collision detection vision systems. Two LGMD neurons, namely LGMD1 and LGMD2, have undergone extensive modeling, each exhibiting distinct collision selectivity toward brighter or darker objects approaching relative to the background. Despite these advancements, a gap exists between biological organisms and the latest models, particularly in implementing diverse collision selectivity and maintaining robustness against objects with varying brightness. To reduce the gap, we introduce a neural model with feedback connections that integrates a feedforward neural network based on ON/OFF channels and feedback loops of ON channels operating merely ON-contrast signals. The instantaneous feedback leads to a fixed-point theorem, establishing the coefficient range in the feedback loop mathematically. This research emphasizes and theoretically analyzes the influence of feedback neural computation on collision perception. To validate the model's effectiveness, we define an evaluation criterion, i.e., the time error to collision (TTC), and compare the proposed model with typical LGMD1 and LGMD2 models. Systematic experiments demonstrate that the proposed model achieves specific collision selectivity comparable to both LGMD1 and LGMD2 while exhibiting enhanced robustness against objects with changing brightness on the surface, outperforming the comparative models. The proposed model predicts collision danger more accurately and robustly, yielding lower TTC. Finally, we carry out on-line robot experiments to investigate the model's collision selectivity. The performance proves the practicality and efficiency of feedback neural computation in embedded vision system.

Paying attention to natural scenes in area V1

Article

Full-text available

Feb 2024

Natural scene responses in the primary visual cortex are modulated simultaneously by attention and by contextual signals about scene statistics stored across the connectivity of the visual processing hierarchy. We hypothesized that attentional and contextual signals interact in V1 in a manner that primarily benefits the representation of natural stimuli, rich in high-order statistical structure. Recording from two macaques engaged in a spatial attention task, we found that attention enhanced the decodability of stimulus identity from population responses evoked by natural scenes, but not by synthetic stimuli lacking higher-order statistical regularities. Population analysis revealed that neuronal responses converged to a low-dimensional subspace only for natural stimuli. Critically, we determined that the attentional enhancement in stimulus decodability was captured by the natural-scene subspace, indicating an alignment between the attentional and natural stimulus variance. These results suggest that attentional and contextual signals interact in V1 in a manner optimized for natural vision.

A CODE model bridging crowding in sparse and dense displays

Article

Full-text available

Feb 2024
VISION RES

Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a relatively well-understood phenomenon. However, most investigations and theories are based on sparse displays consisting of a target and at most a handful of flanker objects. Recent findings suggest that the laws thought to govern crowding may not hold for densely cluttered displays, and that grouping and nearest neighbour effects may be more important. Here we present a computational model that accounts for crowding effects in both sparse and dense displays. The model is an adaptation and extension of an earlier model that has previously successfully accounted for spatial clustering, numerosity and object-based attention phenomena. Our model combines grouping by proximity and similarity with a nearest neighbour rule, and defines crowding as the extent to which target and flankers fail to segment. We show that when the model is optimized for explaining crowding phenomena in classic, sparse displays, it also does a good job in capturing novel crowding patterns in dense displays, in both existing and new data sets. The model thus ties together different principles governing crowding, specifically Bouma's law, grouping, and nearest neighbour similarity effects.

Gestalt neurons and emergent properties in visual perception: A novel concept for the transformation from local to global processing

Article

Full-text available

Dec 2023
J VISION

Gestalten in visual perception are defined by emergent properties of the whole, which cannot be predicted from the sum of its parts; rather, they arise by virtue of inherent principles, the Laws of Seeing. This review attempts to assign neurophysiological correlates to select emergent properties in motion and contour perception and proposes parallels to the processing of local versus global attributes by classical versus contextual receptive fields. The aim is to identify Gestalt neurons in the visual system to account for the Laws of Seeing in causal terms and to explain "Why do things look as they do" (Koffka, 1935, p. 76).

Repetition Priming Reveals Sustained Facilitation and Transient Inhibition in Reaction Time

Article

Full-text available

Aug 2000

Reaction time (RT) in a detection or a location discrimination task increases when a target is repeatedly presented at the same location (inhibition), whereas RT decreases in feature (color or orientation) discrimination tasks (facilitation; Y. Tanaka & S. Shimojo, 1996a). Here, the time course of inhibition and facilitation was examined, using a repetition priming paradigm. Results indicate that inhibition occurred only in the immediately successive trial, whereas facilitation accumulated over several trials with location repetition. Moreover, inhibition and facilitation occurred in a task-relevant manner: Detection–location discrimination tasks produced transient RT increase, whereas feature discrimination tasks produced cumulative RT decrease. These results suggest a functional dissociation between spatial orienting and feature analysis, as well as top-down modulations by tasks leading to different types of visual memory.

Covert Visual Search: A Comparison of Performance by Humans and Macaques (Macaca mulatta)

Article

Full-text available

Jun 1999

The duration of the visual search by human participants for visual features is independent of the number of targets being viewed. In contrast, search for targets formed by conjunction of features is characterized by reaction times that increase as a linear function of the number of items viewed, suggesting that the target detection requires scrutiny of the search array by focal attention. Macaque (Macaca mulatta) and human performance on feature and conjunction search tasks was compared by using color or motion, or by conjunctions of color and motion. Like human participants, monkeys exhibited a dichotomy between feature and conjunction search performance. This finding suggests that humans and macaques engage similar brain mechanisms for representation of feature and conjunction targets. This behavioral paradigm can thus be used in neurophysiological experiments directed at the mechanisms of feature integration and target selection.

Local minimization of prediction errors drives learning of invariant object representations in a generative network model of visual perception

Article

Full-text available

Sep 2023

The ventral visual processing hierarchy of the cortex needs to fulfill at least two key functions: perceived objects must be mapped to high-level representations invariantly of the precise viewing conditions, and a generative model must be learned that allows, for instance, to fill in occluded information guided by visual experience. Here, we show how a multilayered predictive coding network can learn to recognize objects from the bottom up and to generate specific representations via a top-down pathway through a single learning rule: the local minimization of prediction errors. Trained on sequences of continuously transformed objects, neurons in the highest network area become tuned to object identity invariant of precise position, comparable to inferotemporal neurons in macaques. Drawing on this, the dynamic properties of invariant object representations reproduce experimentally observed hierarchies of timescales from low to high levels of the ventral processing stream. The predicted faster decorrelation of error-neuron activity compared to representation neurons is of relevance for the experimental search for neural correlates of prediction errors. Lastly, the generative capacity of the network is confirmed by reconstructing specific object images, robust to partial occlusion of the inputs. By learning invariance from temporal continuity within a generative model, the approach generalizes the predictive coding framework to dynamic inputs in a more biologically plausible way than self-supervised networks with non-local error-backpropagation. This was achieved simply by shifting the training paradigm to dynamic inputs, with little change in architecture and learning rule from static input-reconstructing Hebbian predictive coding networks.

A mechanistic account of visual discomfort

Article

Full-text available

Jul 2023

Much of the neural machinery of the early visual cortex, from the extraction of local orientations to contextual modulations through lateral interactions, is thought to have developed to provide a sparse encoding of contour in natural scenes, allowing the brain to process efficiently most of the visual scenes we are exposed to. Certain visual stimuli, however, cause visual stress, a set of adverse effects ranging from simple discomfort to migraine attacks, and epileptic seizures in the extreme, all phenomena linked with an excessive metabolic demand. The theory of efficient coding suggests a link between excessive metabolic demand and images that deviate from natural statistics. Yet, the mechanisms linking energy demand and image spatial content in discomfort remain elusive. Here, we used theories of visual coding that link image spatial structure and brain activation to characterize the response to images observers reported as uncomfortable in a biologically based neurodynamic model of the early visual cortex that included excitatory and inhibitory layers to implement contextual influences. We found three clear markers of aversive images: a larger overall activation in the model, a less sparse response, and a more unbalanced distribution of activity across spatial orientations. When the ratio of excitation over inhibition was increased in the model, a phenomenon hypothesised to underlie interindividual differences in susceptibility to visual discomfort, the three markers of discomfort progressively shifted toward values typical of the response to uncomfortable stimuli. Overall, these findings propose a unifying mechanistic explanation for why there are differences between images and between observers, suggesting how visual input and idiosyncratic hyperexcitability give rise to abnormal brain responses that result in visual stress.

The Neurophysiology of Attention and Object Recognition in Visual Scenes

Chapter

Full-text available

Oct 2014

Cutting-edge research on the visual cognition of scenes, covering issues that include spatial vision, context, emotion, attention, memory, and neural mechanisms underlying scene representation. For many years, researchers have studied visual recognition with objects—single, clean, clear, and isolated objects, presented to subjects at the center of the screen. In our real environment, however, objects do not appear so neatly. Our visual world is a stimulating scenery mess; fragments, colors, occlusions, motions, eye movements, context, and distraction all affect perception. In this volume, pioneering researchers address the visual cognition of scenes from neuroimaging, psychology, modeling, electrophysiology, and computer vision perspectives. Building on past research—and accepting the challenge of applying what we have learned from the study of object recognition to the visual cognition of scenes—these leading scholars consider issues of spatial vision, context, rapid perception, emotion, attention, memory, and the neural mechanisms underlying scene representation. Taken together, their contributions offer a snapshot of our current knowledge of how we understand scenes and the visual world around us. ContributorsElissa M. Aminoff, Moshe Bar, Margaret Bradley, Daniel I. Brooks, Marvin M. Chun, Ritendra Datta, Russell A. Epstein, Michèle Fabre-Thorpe, Elena Fedorovskaya, Jack L. Gallant, Helene Intraub, Dhiraj Joshi, Kestutis Kveraga, Peter J. Lang, Jia Li Xin Lu, Jiebo Luo, Quang-Tuan Luong, George L. Malcolm, Shahin Nasr, Soojin Park, Mary C. Potter, Reza Rajimehr, Dean Sabatinelli, Philippe G. Schyns, David L. Sheinberg, Heida Maria Sigurdardottir, Dustin Stansbury, Simon Thorpe, Roger Tootell, James Z. Wang

Explaining V1 Properties with a Biologically Constrained Deep Learning Architecture

Preprint

Full-text available

May 2023

Convolutional neural networks (CNNs) have recently emerged as promising models of the ventral visual stream, despite their lack of biological specificity. While current state-of-the-art models of the primary visual cortex (V1) have surfaced from training with adversarial examples and extensively augmented data, these models are still unable to explain key neural properties observed in V1 that arise from biological circuitry. To address this gap, we systematically incorporated neuroscience-derived architectural components into CNNs to identify a set of mechanisms and architectures that comprehensively explain neural activity in V1. We show drastic improvements in model-V1 alignment driven by the integration of architectural components that simulate center-surround antagonism, local receptive fields, tuned normalization, and cortical magnification. Upon enhancing task-driven CNNs with a collection of these specialized components, we uncover models with latent representations that yield state-of-the-art explanation of V1 neural activity and tuning properties. Our results highlight an important advancement in the field of NeuroAI, as we systematically establish a set of architectural components that contribute to unprecedented explanation of V1. The neuroscience insights that could be gleaned from increasingly accurate in-silico models of the brain have the potential to greatly advance the fields of both neuroscience and artificial intelligence.

Characterizing spatiotemporal population receptive fields in human visual cortex with fMRI

Preprint

Full-text available

May 2023

The use of fMRI and computational modeling has advanced understanding of spatial characteristics of population receptive fields (pRFs) in human visual cortex. However, we know relatively little about the spatiotemporal characteristics of pRFs because neurons’ temporal properties are one to two orders of magnitude faster than fMRI BOLD responses. Here, we developed an image-computable framework to estimate spatiotemporal pRFs from fMRI data. First, we developed a simulation software that predicts fMRI responses to a time varying visual input given a spatiotemporal pRF model and solves the model parameters. The simulator revealed that ground-truth spatiotemporal parameters can be accurately recovered at the millisecond resolution from synthesized fMRI responses. Then, using fMRI and a novel stimulus paradigm, we mapped spatiotemporal pRFs in individual voxels across human visual cortex in 10 participants. We find that a compressive spatiotemporal (CST) pRF model better explains fMRI responses than a conventional spatial pRF model across visual areas spanning the dorsal, lateral, and ventral streams. Further, we find three organizational principles of spatiotemporal pRFs: (i) from early to later areas within a visual stream, spatial and temporal integration windows of pRFs progressively increase in size and show greater compressive nonlinearities, (ii) later visual areas show diverging spatial and temporal integration windows across streams, and (iii) within early visual areas (V1-V3), both spatial and temporal integration windows systematically increase with eccentricity. Together, this computational framework and empirical results open exciting new possibilities for modeling and measuring fine-grained spatiotemporal dynamics of neural responses in the human brain using fMRI. Significance Statement We developed a computational framework for estimating spatiotemporal receptive fields of neural populations using fMRI. This framework pushes the boundary of fMRI measurements, enabling quantitative evaluation of neural spatial and temporal processing windows at the resolution of visual degrees and milliseconds, which was thought to be unattainable with fMRI. We not only replicate well-established visual field and pRF size maps, but also estimates of temporal summation windows from electrophysiology. Notably, we find that spatial and temporal windows as well as compressive nonlinearities progressively increase from early to later visual areas in multiple visual processing streams. Together, this framework opens exciting new possibilities for modeling and measuring fine-grained spatiotemporal dynamics of neural responses in the human brain using fMRI.

Contributions of low- and high-level contextual mechanisms to human face perception

Article

Full-text available

May 2023
PLOS ONE

Contextual modulations at primary stages of visual processing depend on the strength of local input. Contextual modulations at high-level stages of (face) processing show a similar dependence to local input strength. Namely, the discriminability of a facial feature determines the amount of influence of the face context on that feature. How high-level contextual modulations emerge from primary mechanisms is unclear due to the scarcity of empirical research systematically addressing the functional link between the two. We tested (62) young adults' ability to process local input independent of the context using contrast detection and (upright and inverted) morphed facial feature matching tasks. We first investigated contextual modulation magnitudes across tasks to address their shared variance. A second analysis focused on the profile of performance across contextual conditions. In upright eye matching and contrast detection tasks, contextual modulations only correlated at the level of their profile (averaged Fisher-Z transformed r = 1.18, BF10 > 100), but not magnitude (r = .15, BF10 = .61), suggesting the functional independence but similar working principles of the mechanisms involved. Both the profile (averaged Fisher-Z transformed r = .32, BF10 = 9.7) and magnitude (r = .28, BF10 = 4.58) of the contextual modulations correlated between inverted eye matching and contrast detection tasks. Our results suggest that non-face-specialized high-level contextual mechanisms (inverted faces) work in connection to primary contextual mechanisms, but that the engagement of face-specialized mechanisms for upright faces obscures this connection. Such combined study of low- and high-level contextual modulations sheds new light on the functional relationship between different levels of the visual processing hierarchy, and thus on its functional organization.

Paying attention to natural scenes in area V1

Preprint

Full-text available

Mar 2023

Natural scene responses in the primary visual cortex are modulated simultaneously by attention and by contextual signals about scene statistics stored across the connectivity of the visual processing hierarchy. We hypothesize that attentional and contextual top-down signals interact in V1, in a manner that primarily benefits the representation of natural visual stimuli, rich in high-order statistical structure. Recording from two macaques engaged in a spatial attention task, we show that attention enhances the decodability of stimulus identity from population responses evoked by natural scenes but, critically, not by synthetic stimuli in which higher-order statistical regularities were eliminated. Attentional enhancement of stimulus decodability from population responses occurs in low dimensional spaces, as revealed by principal component analysis, suggesting an alignment between the attentional and the natural stimulus variance. Moreover, natural scenes produce stimulus-specific oscillatory responses in V1, whose power undergoes a global shift from low to high frequencies with attention. We argue that attention and perception share top-down pathways, which mediate hierarchical interactions optimized for natural vision.

LFP polarity changes across cortical and eccentricity in primary visual cortex

Article

Full-text available

Feb 2023

Local field potentials (LFPs) can evaluate neural population activity in the cortex and their interaction with other cortical areas. Analyzing current source density (CSD) rather than LFPs is very significant due to the reduction of volume conduction effects. Current sinks are construed as net inward transmembrane currents, while current sources are net outward ones. Despite extensive studies of LFPs and CSDs, their morphology in different cortical layers and eccentricities are still largely unknown. Because LFP polarity changes provide a measure of neural activity, they can be useful in implanting brain-computer interface (BCI) chips and effectively communicating the BCI devices to the brain. We hypothesize that sinks and sources analyses could be a way to quantitatively achieve their characteristics in response to changes in stimulus size and layer-dependent differences with increasing eccentricities. In this study, we show that stimulus properties play a crucial role in determining the flow. The present work focusses on the primary visual cortex (V1). In this study, we investigate a map of the LFP-CSD in V1 area by presenting different stimulus properties (e.g., size and type) in the visual field area of Macaque monkeys. Our aim is to use the morphology of sinks and sources to measure the input and output information in different layers as well as different eccentricities. According to the value of CSDs, the results show that the stimuli smaller than RF’s size had lower strength than the others and the larger RF’s stimulus size showed smaller strength than the optimized stimulus size, which indicated the suppression phenomenon. Additionally, with the increased eccentricity, CSD’s strengths were increased across cortical layers.

Hierarchy of Intra- and Cross-modal Redundancy Gains in Visuo-tactile Search: Evidence from the Posterior Contralateral Negativity

Article

Feb 2023
J COGNITIVE NEUROSCI

Redundant combination of target features from separable dimensions can expedite visual search. The dimension-weighting account explains these "redundancy gains" by assuming that the attention-guiding priority map integrates the feature-contrast signals generated by targets within the respective dimensions. The present study investigated whether this hierarchical architecture is sufficient to explain the gains accruing from redundant targets defined by features in different modalities, or whether an additional level of modality-specific priority coding is necessary, as postulated by the modality-weighting account (MWA). To address this, we had observers perform a visuo-tactile search task in which targets popped out by a visual feature (color or shape) or a tactile feature (vibro-tactile frequency) as well as any combination of these features. The RT gains turned out larger for visuo-tactile versus visual redundant targets, as predicted by the MWA. In addition, we analyzed two lateralized event-related EEG components: the posterior (PCN) and central (CCN) contralateral negativities, which are associated with visual and tactile attentional selection, respectively. The CCN proved to be a stable somatosensory component, unaffected by cross-modal redundancies. In contrast, the PCN was sensitive to cross-modal redundancies, evidenced by earlier onsets and higher amplitudes, which could not be explained by linear superposition of the earlier CCN onto the later PCN. Moreover, linear mixed-effect modeling of the PCN amplitude and timing parameters accounted for approximately 25% of the behavioral RT variance. Together, these behavioral and PCN effects support the hierarchy of priority-signal computation assumed by the MWA.

Cognitive-Based Crack Detection for Road Maintenance: An Integrated System in Cyber-Physical-Social Systems

Article

Full-text available

Jan 2022

Effective road maintenance can not only achieve a balance between limited resources and long-term high-efficiency performance of road but also reduce the loss of life and property caused by road damage to vehicles and pedestrians. Due to the lack of a multidimensional dynamic monitoring system and enough extremely special data, the existing road maintenance system cannot accurately assess the road surface condition and provide timely early warning of sudden road damage. In this article, the M-RM system is proposed, that is, a metaverse-enabled road maintenance system based on cyber–physical–social systems (CPSSs), which fully utilizes the social and artificial system information of CPSS, as well as the simulation, monitoring, diagnosis and prediction functions of road systems in the virtual world of the metaverse. Then, in the road damage detection of system model in the virtual world, for the virtual data of the core assets of the metaverse, we propose an adaptive and information-preserving data augmentation (AIDA) algorithm-based nonclassical receptive field suppression and enhancement, an algorithm developed from human visual cognition. This algorithm enables the generation of a large amount of scarce fidelity data and avoids the introduced noise from impairing the performance of nonaugmented data. Finally, a crack detection algorithm named pay attention twice (PAT) is proposed, which uses the generated virtual data for training, and achieves secondary attention to high-frequency targets by fusing frequency-division convolution and mixed-domain attention mechanism. The detection performance of small targets in uncertain environments is enhanced. The metaverse system built in the current research can not only be used for road maintenance but also empower the traffic metaverse by using the traffic flow prediction module embedded in the algorithm. Experimental results demonstrate that the proposed algorithm can be applied to the road damage detection task under different noise and weather conditions, and the performance outweighs other state-of-the-art algorithms.

Eye tracking evidence for V1 Saliency Hypothesis from an anomalous visual search behavior

Article

Dec 2022
J VISION

The Neurophysiology of Attention and Object Recognition in Visual Scenes

Chapter

Full-text available

Nov 2014

This chapter examines some neural processes that a scene image undergoes as it moves through the visual system. It focuses on two opposite yet highly interactive neural systems, the frontoparietal network and the ventral visual stream. Visual recognition mechanisms in the ventral stream lean toward certain objects in visual scenes because they occupy a space that has already been allotted for a high priority by the lateral intraparietal area and the frontal eye fields. While the ventral visual system processes and determines the objects in that environment, the frontoparietal network allocates and points visual attention to important features of the environment.This division of labor by the two systems is supported by the view that spatial selection and target identification are separable parts of finding objects in visual scenes.

A microcircuit model involving parvalbumin, somatostatin, and vasoactive intestinal polypeptide inhibitory interneurons for the modulation of neuronal oscillation during visual processing

Article

Full-text available

Sep 2022

Various subtypes of inhibitory interneurons contact one another to organize cortical networks. Most cortical inhibitory interneurons express 1 of 3 genes: parvalbumin (PV), somatostatin (SOM), or vasoactive intestinal polypeptide (VIP). This diversity of inhibition allows the flexible regulation of neuronal responses within and between cortical areas. However, the exact roles of these interneuron subtypes and of excitatory pyramidal (Pyr) neurons in regulating neuronal network activity and establishing perception (via interactions between feedforward sensory and feedback attentional signals) remain largely unknown. To explore the regulatory roles of distinct neuronal types in cortical computation, we developed a computational microcircuit model with biologically plausible visual cortex layers 2/3 that combined Pyr neurons and the 3 inhibitory interneuron subtypes to generate network activity. In simulations with our model, inhibitory signals from PV and SOM neurons preferentially induced neuronal firing at gamma (30–80 Hz) and beta (20–30 Hz) frequencies, respectively, in agreement with observed physiological results. Furthermore, our model indicated that rapid inhibition from VIP to SOM subtypes underlies marked attentional modulation for low-gamma frequency (30–50 Hz) in Pyr neuron responses. Our results suggest the distinct but cooperative roles of inhibitory interneuron subtypes in the establishment of visual perception.

Machine Learning As Tool And Theory For Computational Neuroscience

Article

Jan 2022

Ari S. Benjamin

Computational neuroscience is in the midst of constructing a new framework for understanding the brain based on the ideas and methods of machine learning. This is effort has been encouraged, in part, by recent advances in neural network models. It is also driven by a recognition of the complexity of neural computation and the challenges that this poses for neuroscience’s methods. In this dissertation, I first work to describe these problems of complexity that have prompted a shift in focus. In particular, I develop machine learning tools for neurophysiology that help test whether tuning curves and other statistical models in fact capture the meaning of neural activity. Then, taking up a machine learning framework for understanding, I consider theories about how neural computation emerges from experience. Specifically, I develop hypotheses about the potential learning objectives of sensory plasticity, the potential learning algorithms in the brain, and finally the consequences for sensory representations of learning with such algorithms. These hypotheses pull from advances in several areas of machine learning, including optimization, representation learning, and deep learning theory. Each of these subfields has insights for neuroscience, offering up links for a chain of knowledge about how we learn and think. Together, this dissertation helps to further an understanding of the brain in the lens of machine learning.

Macaque V1 responses to 2nd-order contrast-modulated stimuli and the possible subcortical and cortical contributions

Article

Full-text available

Jul 2022
PROG NEUROBIOL

Natural images comprise contours and boundaries defined by 1st-order luminance-modulated (LM) cues that are readily encoded by V1 neurons, and 2nd-order contrast-modulated (CM) cues that carry local, but not over-the-space, luminance changes. The neurophysiological foundations for CM processing remain unsolved. Here we used two-photon calcium imaging to demonstrate that V1 superficial-layer neurons respond to both LM and CM gratings in awake fixating macaques, with overall LM responses stronger than CM responses. Furthermore, adaptation experiments revealed that LM responses were similarly suppressed by LM and CM adaptation, with moderately larger effects by iso-orientation adaptation than by orthogonal adaptation, suggesting that LM and CM orientation responses likely share a strong orientation-non-selective subcortical origin. In contrast, CM responses were substantially more suppressed by iso-orientation than by orthogonal LM and CM adaptation, likely suggesting stronger orientation-specific intracortical influences for CM responses than for LM responses, besides shared orientation-non-selective subcortical influences. These results thus may indicate a subcortical-to-V1 filter-rectify-filter mechanism for CM processing: Local luminance changes in CM stimuli are initially encoded by orientation-non-selective subcortical neurons, and the outputs are half-wave rectified, and then summed by V1 neurons to signal CM orientation, which may be further substantially refined by intracortical influences. https://doi.org/10.1016/j.pneurobio.2022.102315

The Visual Cortical Responses to Sinusoidal Transcorneal Electrical Stimulation

Article

Mar 2022
BRAIN RES

Retinal stimulation has become a widely utilized approach to restore visual function for individuals with retinal degenerative diseases. Although the rectangular electrical pulse is the primary stimulus waveform used in retinal neuromodulation, it remains unclear whether alternate waveforms may be more effective. Here, we used the optical intrinsic signal imaging system to assess the responses of cats’ visual cortex to sinusoidal electrical stimulation through contact lens electrode, analyzing the response to various stimulus parameters (frequency, intensity, pulse width). A comparison between sinusoidal and rectangular stimulus waveform was also investigated. The results indicated that the optimal stimulation frequency for sinusoidal electrical stimulation was approximately 20 Hz, supporting the hypothesis that low-frequency electrostimulation induces more responsiveness in retinal neurons than high-frequency electrostimulation in case of sinusoidal stimulation. We also demonstrated that for low-frequency retinal neuromodulation, sinusoidal pulses are more effective than rectangular ones. In addition, we found that compared to current intensity, the effect of the sinusoidal pulse width on cortical responses was more prominent. These results suggested that sinusoidal electrical stimulation may provide a promising strategy for improved retinal neuromodulation in clinical settings.

Macaque Area V2/V3 Reorganization Following Homonymous Retinal Lesions

Article

Full-text available

Jan 2022

In the adult visual system, topographic reorganization of the primary visual cortex (V1) after retinal lesions has been extensively investigated. In contrast, the plasticity of higher order extrastriate areas following retinal lesions is less well studied. Here, we used fMRI to study reorganization of visual areas V2/V3 following the induction of permanent, binocular, homonymous retinal lesions in 4 adult macaque monkeys. We found that the great majority of voxels that did not show visual modulation on the day of the lesion in the V2/V3 lesion projection zone (LPZ) demonstrated significant visual modulations 2 weeks later, and the mean modulation strength remained approximately stable thereafter for the duration of our observations (4–5 months). The distribution of eccentricities of visually modulated voxels inside the V2/V3 LPZ spanned a wider range post-lesion than pre-lesion, suggesting that neurons inside the LPZ reorganize by receiving input either from the foveal or the peripheral border of the LPZ, depending on proximity. Overall, we conclude that area V2/V3 of adult rhesus macaques displays a significant capacity for topographic reorganization following retinal lesions markedly exceeding the corresponding capacity of area V1.

Rhythms of prefrontal cognitive functions

Thesis

Dec 2020

Corentin Gaillard

While the access to motor function from brain activity have been successfully achieved in the last decade, the understanding of how the brain implements cognitive processes and accessing to this information at a high temporal and informational resolution remains challenging. Indeed, cognition is built upon interconnected multi-scaled networks and rely on complex population encoding. This doctoral thesis using visual attention as a model introduces multiple neurophysiological concepts, allowing a highly resolved access in terms of information content and temporal precision and an enhanced understanding of how cognitive processes are implemented in the prefrontal cortex. The first axis of this work focuses on accessing cognitive information using multiple recorded signals (MUA, LFP). In the prefrontal cortex cognitive processes rely on dynamic and population neuronal activity. Therefore, prior qualitative selection of input information highly improves access to covert cognitive mechanisms as attention. Once achieved at a high performance and resolution, this decoded information gives us a precious insight into FEF attentional spotlight rhythmic encoding at the population scale. Specifically, this readout reveals inner properties of attentional sampling mechanisms. In particular, we show that the FEF population implements of a rhythmic alpha attentional sampling of visual space. In a second axis, we expand our approach to multiple cognitive scales. First, using a similar attentional decoding procedure as in the first axis, we analyzed the prefrontal implementation of attentional processes at very slow temporal scales, up to several hours. We report for the first time that sustained attention actually oscillates at an ultra-slow rhythm, organizing alternation of optimal and suboptimal perceptual periods every 7 to 15 minutes with high behavioral impact. Finally, at the scale of the trial, we show that functional neuronal correlations between pairs of neurons are described to play a critical role in neuronal information processing and optimal neuronal computations during attention. Here, we demonstrate that neuronal inter-correlations are actually a functional process under rhythmic modulation, locally implementing long range influences and shaping our cognitive performances. On the whole, this thesis contributes to a better understanding of how cognitive processes are implemented in the prefrontal cortex. Importantly, focusing on multiple temporal approaches, we demonstrate that cognitive processes are built upon multi scale rhythmic activity, critically shaping our perception of the world. Crucially, we discuss the fact that these new scales and rhythms represent promising targets to modulate, restore, and hopefully enhance our cognitive abilities.

Parallel Advantage: Further Evidence for Bottom-up Saliency Computation by Human Primary Visual Cortex

Article

Full-text available

Jan 2022

Li Zhaoping

Finding a target among uniformly oriented non-targets is typically faster when this target is perpendicular, rather than parallel, to the non-targets. The V1 Saliency Hypothesis (V1SH), that neurons in the primary visual cortex (V1) signal saliency for exogenous attentional attraction, predicts exactly the opposite in a special case: each target or non-target comprises two equally sized disks displaced from each other by 1.2 disk diameters center-to-center along a line defining its orientation. A target has two white or two black disks. Each non-target has one white disk and one black disk, and thus, unlike the target, activates V1 neurons less when its orientation is parallel rather than perpendicular to the neurons’ preferred orientations. When the target is parallel, rather than perpendicular, to the uniformly oriented non-targets, the target’s evoked V1 response escapes V1’s iso-orientation surround suppression, making the target more salient. I present behavioral observations confirming this prediction.

Surround Modulation Properties of Tectal Neurons in Pigeon Characterized by Moving and Flashed Stimuli

Preprint

Dec 2021

Perceptual Texture Dimensions Modulate Neuronal Response Dynamics in Visual Cortical Area V4

Article

Full-text available

Dec 2021

Texture is an important visual attribute for surface pattern discrimination and therefore object segmentation, but the neural bases of texture perception are largely unknown. Previously, we demonstrated that the responses of V4 neurons to naturalistic texture patches are sensitive to four key features of human texture perception: coarseness, directionality, regularity, and contrast. To begin to understand how distinct texture perception emerges from the dynamics of neuronal responses, in 2 macaque monkeys (1 male, 1 female), we investigated the relative contribution of the four texture attributes to V4 responses in terms of the strength and timing of response modulation. We found that the different feature dimensions are associated with different temporal dynamics. Specifically, the response modulation associated with directionality and regularity was significantly delayed relative to that associated with coarseness and contrast, suggesting that the latter are fundamentally simpler feature dimensions. The population of texture-selective neurons could be grouped into multiple clusters based on the combination of feature dimensions encoded, and those subpopulations displayed distinct temporal dynamics characterized by the weighted combinations of multiple features. Finally, we applied a population decoding approach to demonstrate that texture category information can be obtained from short temporal windows across time. These results demonstrate that the representation of different perceptually relevant texture features emerge over time in the responses of V4 neurons. The observed temporal organization provides a framework to interpret how the processing of surface features unfolds in early and midlevel cortical stages, and could ultimately inform the interpretation of perceptual texture dynamics.Significance Statement:To delineate how neuronal responses underlie our ability to perceive visual textures, we related four key perceptual dimensions (coarseness, directionality, regularity, and contrast) of naturalistic textures to the strength and timing of modulation of neuronal responses in area V4, an intermediate stage in the form-processing, ventral visual pathway. Our results provide the first characterization of V4 temporal dynamics for texture encoding along perceptually defined axes.

Population receptive fields in non-human primates from whole-brain fMRI and large-scale neurophysiology in visual cortex in visual cortex

Article

Full-text available

Nov 2021
eLife

Population receptive field (pRF) modeling is a popular fMRI method to map the retinotopic organization of the human brain. While fMRI-based pRF-maps are qualitatively similar to invasively recorded single-cell receptive fields in animals, it remains unclear what neuronal signal they represent. We addressed this question in awake non-human primates comparing whole-brain fMRI and large-scale neurophysiological recordings in areas V1 and V4 of the visual cortex. We examined the fits of several pRF-models based on the fMRI BOLD-signal, multi-unit spiking activity (MUA) and local field potential (LFP) power in different frequency bands. We found that pRFs derived from BOLD-fMRI were most similar to MUA-pRFs in V1 and V4, while pRFs based on LFP gamma power also gave a good approximation. FMRI-based pRFs thus reliably reflect neuronal receptive field properties in the primate brain. In addition to our results in V1 and V4, the whole-brain fMRI measurements revealed retinotopic tuning in many other cortical and subcortical areas with a consistent increase in pRF-size with increasing eccentricity, as well as a retinotopically specific deactivation of default-mode network nodes similar to previous observations in humans.

Statistical Learning of Frequent Distractor Locations in Visual Search Involves Regional Signal Suppression in Early Visual Cortex

Article

Full-text available

Nov 2021

Observers can learn locations where salient distractors appear frequently to reduce potential interference—an effect attributed to better suppression of distractors at frequent locations. But how distractor suppression is implemented in the visual cortex and within the frontoparietal attention networks remains unclear. We used fMRI and a regional distractor-location learning paradigm with two types of distractors defined in either the same (orientation) or a different (color) dimension to the target to investigate this issue. fMRI results showed that BOLD signals in early visual cortex were significantly reduced for distractors (as well as targets) occurring at the frequent versus rare locations, mirroring behavioral patterns. This reduction was more robust with same-dimension distractors. Crucially, behavioral interference was correlated with distractor-evoked visual activity only for same- (but not different-) dimension distractors. Moreover, with different- (but not same-) dimension distractors, a color-processing area within the fusiform gyrus was activated more when a distractor was present in the rare region versus being absent and more with a distractor in the rare versus frequent locations. These results support statistical learning of frequent distractor locations involving regional suppression in early visual cortex and point to differential neural mechanisms of distractor handling with different- versus same-dimension distractors.

Deep saliency models learn low-, mid-, and high-level features to predict scene attention

Article

Full-text available

Sep 2021

Deep saliency models represent the current state-of-the-art for predicting where humans look in real-world scenes. However, for deep saliency models to inform cognitive theories of attention, we need to know how deep saliency models prioritize different scene features to predict where people look. Here we open the black box of three prominent deep saliency models (MSI-Net, DeepGaze II, and SAM-ResNet) using an approach that models the association between attention, deep saliency model output, and low-, mid-, and high-level scene features. Specifically, we measured the association between each deep saliency model and low-level image saliency, mid-level contour symmetry and junctions, and high-level meaning by applying a mixed effects modeling approach to a large eye movement dataset. We found that all three deep saliency models were most strongly associated with high-level and low-level features, but exhibited qualitatively different feature weightings and interaction patterns. These findings suggest that prominent deep saliency models are primarily learning image features associated with high-level scene meaning and low-level image saliency and highlight the importance of moving beyond simply benchmarking performance.

Synapse-type-specific competitive Hebbian learning forms functional recurrent networks

Article

Jun 2024
P NATL ACAD SCI USA

Cortical networks exhibit complex stimulus–response patterns that are based on specific recurrent interactions between neurons. For example, the balance between excitatory and inhibitory currents has been identified as a central component of cortical computations. However, it remains unclear how the required synaptic connectivity can emerge in developing circuits where synapses between excitatory and inhibitory neurons are simultaneously plastic. Using theory and modeling, we propose that a wide range of cortical response properties can arise from a single plasticity paradigm that acts simultaneously at all excitatory and inhibitory connections—Hebbian learning that is stabilized by the synapse-type-specific competition for a limited supply of synaptic resources. In plastic recurrent circuits, this competition enables the formation and decorrelation of inhibition-balanced receptive fields. Networks develop an assembly structure with stronger synaptic connections between similarly tuned excitatory and inhibitory neurons and exhibit response normalization and orientation-specific center-surround suppression, reflecting the stimulus statistics during training. These results demonstrate how neurons can self-organize into functional networks and suggest an essential role for synapse-type-specific competitive learning in the development of cortical circuits.

Peripheral vision is mainly for looking rather than seeing

Article

Nov 2023
NEUROSCI RES

Li Zhaoping

Characterizing Spatiotemporal Population Receptive Fields in Human Visual Cortex with fMRI

Article

Nov 2023

Modulation of input sensitivity and output gain by retinal amacrine cells

Preprint

Full-text available

Oct 2023

The prevailing hierarchical view of the visual system consists of parallel circuits that begin in the retina, which then sum effects across sequential levels, increasing in complexity. Yet a separate type of interaction, whereby one visual pattern changes the influence of another, known as modulation, has received much less attention in terms of its circuit mechanisms. Retinal amacrine cells are a diverse class of inhibitory interneurons that are thought to have modulatory effects, but we lack a general understanding of their functional types. Using dynamic causal experiments in the salamander retina perturbing amacrine cells along with an unsupervised computational framework, we find that amacrine cell modulatory effects cluster into two distinct types. One type controls ganglion cell sensitivity to individual visual features, and a second type controls the ganglion cell’s output gain, acting to gate all features. These results establish three separate general roles of amacrine cells – to generate primary visual features, to use context to select specific visual features and to gate retinal output.

Different patterns of foreground and background processing contribute to texture segregation in humans: an electrophysiological study

Article

Oct 2023

Background Figure-ground segregation is a necessary process for accurate visual recognition. Previous neurophysiological and human brain imaging studies have suggested that foreground-background segregation relies on both enhanced foreground representation and suppressed background representation. However, in humans, it is not known when and how foreground and background processing play a role in texture segregation. Methods To answer this question, it is crucial to extract and dissociate the neural signals elicited by the foreground and background of a figure texture with high temporal resolution. Here, we combined an electroencephalogram (EEG) recording and a temporal response function (TRF) approach to specifically track the neural responses to the foreground and background of a figure texture from the overall EEG recordings in the luminance-tracking TRF. A uniform texture was included as a neutral condition. The texture segregation visual evoked potential (tsVEP) was calculated by subtracting the uniform TRF from the foreground and background TRFs, respectively, to index the specific segregation activity. Results We found that the foreground and background of a figure texture were processed differently during texture segregation. In the posterior region of the brain, we found a negative component for the foreground tsVEP in the early stage of foreground-background segregation, and two negative components for the background tsVEP in the early and late stages. In the anterior region, we found a positive component for the foreground tsVEP in the late stage, and two positive components for the background tsVEP in the early and late stages of texture processing. Discussion In this study we investigated the temporal profile of foreground and background processing during texture segregation in human participants at a high time resolution. The results demonstrated that the foreground and background jointly contribute to figure-ground segregation in both the early and late phases of texture processing. Our findings provide novel evidence for the neural correlates of foreground-background modulation during figure-ground segregation in humans.

Eye movement evidence for the V1 Saliency Hypothesis and the Central-peripheral Dichotomy theory in an anomalous visual search task

Article

Aug 2023

Typically, searching for a target among uniformly tilted non-targets is easier when this target is perpendicular, rather than parallel, to the non-targets. The V1 Saliency Hypothesis (V1SH) - that V1 creates a saliency map to guide attention exogenously - predicts exactly the opposite in a special case: each target or non-target is a pair of equally-sized disks, a homo-pair of two disks of the same color, black or white, or a hetero-pair of two disks of the opposite color; the inter-disk displacement defines its orientation. This prediction - parallel advantage - was supported by the finding that parallel targets require shorter reaction times (RTs) to report targets' locations. Furthermore, it is stronger for targets further from the center of search images, as predicted by the Central-peripheral Dichotomy (CPD) theory entailing that saliency effects are stronger in peripheral than in central vision. However, the parallel advantage could arise from a shorter time required to recognize - rather than to shift attention to - the parallel target. By gaze tracking, the present study confirms that the parallel advantage is solely due to the RTs for the gaze to reach the target. Furthermore, when the gaze is sufficiently far from the target during search, saccade to a parallel, rather than perpendicular, target is more likely, demonstrating the Central-peripheral Dichotomy more directly. Parallel advantage is stronger among observers encouraged to let their search be guided by spontaneous gaze shifts, which are presumably guided by bottom-up saliency rather than top-down factors.

Surround suppression in mouse auditory cortex underlies auditory edge detection

Article

Full-text available

Jan 2023
PLOS COMPUT BIOL

Surround suppression (SS) is a fundamental property of sensory processing throughout the brain. In the auditory system, the early processing stream encodes sounds using a one dimensional physical space-frequency. Previous studies in the auditory system have shown SS to manifest as bandwidth tuning around the preferred frequency. We asked whether bandwidth tuning can be found around frequencies away from the preferred frequency. We exploited the simplicity of spectral representation of sounds to study SS by manipulating both sound frequency and bandwidth. We recorded single unit spiking activity from the auditory cortex (ACx) of awake mice in response to an array of broadband stimuli with varying central frequencies and bandwidths. Our recordings revealed that a significant portion of neuronal response profiles had a preferred bandwidth that varied in a regular way with the sound's central frequency. To gain insight into the possible mechanism underlying these responses, we modelled neuronal activity using a variation of the "Mexican hat" function often used to model SS. The model accounted for response properties of single neurons with high accuracy. Our data and model show that these responses in ACx obey simple rules resulting from the presence of lateral inhibitory sidebands, mostly above the excitatory band of the neuron, that result in sensitivity to the location of top frequency edges, invariant to other spectral attributes. Our work offers a simple explanation for auditory edge detection and possibly other computations of spectral content in sounds.

Topographically Localized Modulation of Tectal Cell Spatial Tuning by Complex Natural Scenes

Article

Full-text available

Dec 2022

The tuning properties of neurons in the visual system can be contextually modulated by the statistics of the area surrounding their receptive field (RF), particularly when the surround contains natural features. However, stimuli presented in specific egocentric locations may have greater behavioral relevance, raising the possibility that the extent of contextual modulation may vary with position in visual space. To explore this possibility, we utilized the small size and optical transparency of the larval zebrafish to describe the form and spatial arrangement of contextually modulated cells throughout an entire tectal hemisphere. We found that the spatial tuning of tectal neurons to a prey-like stimulus sharpens when the stimulus is presented against a background with the statistics of complex natural scenes, relative to a featureless background. These neurons are confined to a spatially restricted region of the tectum and have receptive fields centered within a region of visual space in which the presence of prey preferentially triggers hunting behavior. Our results suggest that contextual modulation of tectal neurons by complex backgrounds may facilitate prey-localization in cluttered visual environments.

Visually induced γ band rhythm in spatial summation beyond the receptive field in mouse primary visual cortex

Article

Sep 2022

Recent studies in many kinds of mammals have established the existence of multiple γ rhythms in the cerebral cortex subserving different functions. In the primary visual cortex (V1), visually induced γ rhythms are dependent on stimulus features. However, experimental findings of γ power induced by varying the size of the drifting grating are inconsistent. Here, we reinvestigated the spatial summation properties of visually induced spike and γ rhythm activities in mouse V1. Our results show that drifting sinusoidal grating stimuli mainly induce 2 γ band rhythms, including a low-frequency band (25–45 Hz) and a high-frequency band (55–75 Hz). Unlike previous findings, we discovered that visually induced γ power could also exhibit extrareceptive field (ERF) modulatory properties. The modulation by ERF stimulation could be either suppressive, countersuppressive, or nonsuppressive, mostly similar to the local spike activity. Moreover, further analysis of the neuron group exhibiting surround suppression in both spike and γ activity revealed that the strength of the surround suppression and the receptive field size showed moderate correlations between measurements by spike and γ rhythm activity. Our findings improve the understanding of the characteristics and neural mechanisms of induced γ rhythms in visual spatial summation.

Spike-timing-dependent plasticity enhances chaotic resonance in small-world network

Article

Aug 2022
PHYSICA A

Weak signals can be detected by a nonlinear system with an appropriate chaotic current input, known as the chaotic resonance (CR). Based on Watts–Strogatz small-world network, the effects of Spike-timing-dependent plasticity (STDP) on CR were systematically investigated. Numerical simulations showed that, under moderately strong chaotic current inputs, CR is enhanced due to the increase in average coupling strength after STDP learning. The above-mentioned phenomenon was observed even with changes in frequency and the network topology. For networks with different initial coupling strengths, their responses to weak signals after STDP learning are almost the same, indicating that networks with weaker coupling strengths have better plasticity. In addition, the effects of adjusting STDP windows on CR is also investigated. It was found that CR is promoted by STDP with a relatively larger long-time potentiation window, while, suppressed by a STDP with a relatively larger long-time depression window. Also, the area difference between long-time depression and long-time potentiation windows is highly correlated with average coupling strength after STDP learning. These conclusions might provide novel insights into weak signal detection and information transmission in different adaptive neural networks.

Temporal resolution and temporal extent of orientation repulsion

Article

Nov 2022
VISION RES

A vertical target is perceived as tilted against a slightly tilted inducer surrounding it. To identify the temporal resolution and temporal extent of this phenomenon of orientation repulsion in the same paradigm, we used an alternating pair of inducer stimuli having complementary orientation distributions and quantified repulsion at various alternation frequencies. The duration of each inducer stimulus was inversely proportional to the frequency. When an orthogonal pair of D2 patterns, a type of grating whose luminance modulation in a particular orientation was the second-order partial derivative of an isotropic 2D-Gaussian, was used as the inducer, repulsion occurred when the duration exceeded 20 ms and leveled off at 30 ms and beyond. When a custom-made texture with a narrowband orientation distribution and another texture with a complementary orientation distribution were alternated as the inducer, repulsion gradually increased until the inducer duration reached 200 ms. The gradual increase in repulsion was observed regardless of whether the orientation of the inducer that appeared simultaneously with the target was discernible. These findings reveal that contextual modulation in orientation occurs at a high temporal resolution and continues to a long temporal extent under optimal conditions.

Priority coding in the visual system

Article

Apr 2022
NAT REV NEUROSCI

Although we are continuously bombarded with visual input, only a fraction of incoming visual events is perceived, remembered or acted on. The neural underpinnings of various forms of visual priority coding, including perceptual expertise, goal-directed attention, visual salience, image memorability and preferential looking, have been studied. Here, we synthesize information from these different examples to review recent developments in our understanding of visual priority coding and its neural correlates, with a focus on the role of behaviour to evaluate candidate correlates. We propose that the brain combines different types of priority into a unified priority signal while also retaining the ability to differentiate between them, and that this happens by leveraging partially overlapping low-dimensional neural subspaces for each type of priority that are shared with the downstream neural populations involved in decision-making. Finally, we describe the gulfs in understanding that have resulted from different research approaches, and we point towards future directions that will lead to fundamental insights about neural coding and how prioritization influences visually guided behaviours. Prioritization of visual inputs manifests itself in different behavioural signatures. In this Review, Rust and Cohen describe these signatures and their neural correlates and suggest that the brain uses a unified priority signal from which downstream areas can decode different types of priority.

Latency shortening with enhanced sparseness and responsiveness in V1 during active visual sensing

Article

Full-text available

Apr 2022

In natural vision, neuronal responses to visual stimuli occur due to self-initiated eye movements. Here, we compare single-unit activity in the primary visual cortex (V1) of non-human primates to flashed natural scenes (passive vision condition) to when they freely explore the images by self-initiated eye movements (active vision condition). Active vision enhances the number of neurons responding, and the response latencies become shorter and less variable across neurons. The increased responsiveness and shortened latency during active vision were not explained by increased visual contrast. While the neuronal activities in all layers of V1 show enhanced responsiveness and shortened latency, a significant increase in lifetime sparseness during active vision is observed only in the supragranular layer. These findings demonstrate that the neuronal responses become more distinct in active vision than passive vision, interpreted as consequences of top-down predictive mechanisms.

An overview of edge and object contour detection

Article

Mar 2022
NEUROCOMPUTING

In computer vision, edge and object contour detection is essential for higher-level vision tasks, such as shape matching, visual salience, image segmentation, and object recognition. It has attracted much attention during the past several decades, and many excellent methods have been proposed. In this paper, we make a comprehensive introduction to representative edge and object contour detection methods in the past two decades. Based on the development of these methods, we mainly classify them into two categories: traditional methods and learning-based methods. We further divide traditional methods into local pattern methods, edge grouping methods, active contour models, and bio-inspired methods. Further, we divide learning-based methods into classical learning-based methods and deep learning-based methods. At the same time, we introduce the most popular benchmarks and evaluation measures and quantitatively compare the performances of these promising methods. Moreover, we discuss the challenges across the gap of human vision and suggest some future trends to bridge the gap. We believe that this overview will benefit newcomers and promote the development of edge and object contour detection.

Columnar Specificity of Intrinsic Horizontal and Cortico-Cortical Connections in Cat Visual Cortex

Article

Full-text available

Jul 1989

A prominent and stereotypical feature of cortical circuitry in the striate cortex is a plexus of long-range horizontal connections, running for 6-8 mm parallel to the cortical surface, which has a clustered distribution. This is seen for both intrinsic cortical connections within a particular cortical area and the convergent and divergent connections running between area 17 and other cortical areas. To determine if these connections are related to the columnar functional architecture of cortex, we combined labeling of the horizontal connections by retrograde transport of rhodamine-filled latex microspheres (beads) and labeling of the orientation columns by 2-deoxyglucose autoradiography. We first mapped the distribution of orientation columns in a small region of area 17 or 18, then made a small injection of beads into the center of an orientation column of defined specificity, and after allowing for retrograde transport, labeled vertical orientation columns with the 2-deoxyglucose technique. The retrogradely labeled cells were confined to regions of orientation specificity similar to that of the injection site, indicating that the horizontal connections run between columns of similar orientation specificity. This relationship was demonstrated for both the intrinsic horizontal and corticocortical connections. The extent of the horizontal connections, which allows single cells to integrate information over larger parts of the visual field than that covered by their receptive fields, and the functional specificity of the connections, suggests possible roles for these connections in visual processing.

Neural responses to static and moving texture patterns in visual cortex of the macaque monkey

Article

Full-text available

Jan 1989

Clustered intrinsic connections in cat Visual cortex

Article

Full-text available

May 1983

The intrinsic connections of the cortex have long been known to run vertically, across the cortical layers. In the present study we have found that individual neurons in the cat primary visual cortex can communicate over suprisingly long distances horizontally (up to 4 mm), in directions parallel to the cortical surface. For all of the cells having widespread projections, the collaterals within their axonal fields were distributed in repeating clusters, with an average periodicity of 1 mm. This pattern of extensive clustered projections has been revealed by combining the techniques of intracellular recording and injection of horseradish peroxidase with three-dimensional computer graphic reconstructions. The clustering pattern was most apparent when the cells were rotated to present a view parallel to the cortical surface. The pattern was observed in more than half of the pyramidal and spiny stellate cells in the cortex and was seen in all cortical layers. In our sample, cells made distant connections within their own layer and/or within another layer. The axon of one cell had clusters covering the same area in two layers, and the clusters in the deeper layer were located under those in the upper layer, suggesting a relationship between the clustering phenomenon and columnar cortical architecture. Some pyramidal cells did not project into the white matter, forming intrinsic connections exclusively. Finally, the axonal fields of all our injected cells were asymmetric, extending for greater distances along one cortical axis than along the orthogonal axis. The axons appeared to cover areas of cortex representing a larger part of the visual field than that covered by the excitatory portion of the cell's own receptive field. These connections may be used to generate larger receptive fields or to produce the inhibitory flanks in other cells' receptive fields.

Neural responses to visual texture patterns in middle temporal area of the macaque monkey

Article

Full-text available

Aug 1992

1. We studied how neurons in the middle temporal visual area (MT) of anesthetized macaque monkeys responded to textured and nontextured visual stimuli. Stimuli contained a central rectangular "figure" that was either uniform in luminance or consisted of an array of oriented line segments. The figure moved at constant velocity in one of four orthogonal directions. The region surrounding the figure was either uniform in luminance or contained a texture array (whose elements were identical or orthogonal in orientation to those of the figure), and it either was stationary or moved along with the figure. 2. A textured figure moving across a stationary textured background ("texture bar" stimulus) often elicited vigorous neural responses, but, on average, the responses to texture bars were significantly smaller than to solid (uniform luminance) bars. 3. Many cells showed direction selectivity that was similar for both texture bars and solid bars. However, on average, the direction selectivity measured when texture bars were used was significantly smaller than that for solid bars, and many cells lost significant direction selectivity altogether. The reduction in direction selectivity for texture bars generally reflected a combination of decreased responsiveness in the preferred direction and increased responsiveness in the null (opposite to preferred) direction. 4. Responses to a texture bar in the absence of a texture background ("texture bar alone") were very similar to the responses to solid bars both in the magnitude of response and in the degree of direction selectivity. Conversely, adding a static texture surround to a moving solid bar reduced direction selectivity on average without a reduction in response magnitude. These results indicate that the static surround is largely responsible for the differences in direction selectivity for texture bars versus solid bars. 5. In the majority of MT cells studied, responses to a moving texture bar were largely independent of whether the elements in the bar were of the same orientation as the background elements or of the orthogonal orientation. Thus, for the class of stimuli we used, orientation contrast does not markedly affect the responses of MT neurons to moving texture patterns. 6. The optimum figure length and the shapes of the length tuning curves determined with the use of solid bars and texture bars differed significantly in most of the cells examined. Thus neurons in MT are not simply selective for a particular figure shape independent of whatever cues are used to delineate the figure.

Synaptic physiology of horizontal connections in cat's visual cortex

Article

Full-text available

Jul 1991

Horizontal connections are a principal component of intrinsic cortical circuitry. They arise mainly from pyramidal cells and course parallel to the brain's surface for distances as long as 8 mm, linking columns with shared orientation preference and allowing cells to integrate visual information from outside their receptive fields. We examined the synaptic physiology of the horizontal pathway in slices of the cat's striate cortex and found that activating lateral fibers produced both excitation and inhibition. We recorded the postsynaptic responses of identified pyramidal cells in layer 2 + 3 of area 17 to electrical shocks applied at three sites: in the home column of the impaled neuron either in layer 2 + 3 or 4, or at a lateral distance of 0.9-3 mm in layer 2 + 3. Within the home column, suprathreshold stimuli produced compound EPSPs with action potentials, followed by fast, GABAAergic IPSPs and a slower, GABABergic IPSP. For the distant stimulating site, the threshold response was an EPSP. Stronger shocks frequently evoked a disynaptic, GABAAergic IPSP that truncated the EPSP and could dominate the postsynaptic response. At the resting potential, the horizontally evoked EPSP was too small to elicit spikes. With depolarization of the membrane, however, it grew several hundred-fold. This amplification was blocked by N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium bromide (QX-314), but not by 2-amino-5-phosphonovalerate (APV), indicating that it was mediated by Na+ channels, rather than by NMDA receptors. We propose that the horizontal connections provide the means for stimuli outside the receptive field to modulate activity elicited within its confines. The voltage-dependent enhancement of the laterally evoked EPSP may explain why stimulating the surround by itself fails to drive cells but can facilitate their response to stimuli within the receptive field. The ability to initiate disynaptic inhibition from lateral sites shows that recruiting appropriate groups of horizontal fibers can also have a suppressive effect. Thus, the effect of horizontal input is state dependent, with the size and sign of the laterally evoked response changing according to the balance of converging inputs.

How Well Do Response Changes of Striate Neurons Signal Differences in Orientation: A Study in the Discriminating Monkey

Article

Full-text available

Dec 1990

Just-noticeable differences (JNDs) in orientation were measured in 2 monkeys using a temporal same-different task, with stationary rectangular gratings as stimuli, and compared to those of humans tested in the same setup. The JNDs of one monkey (1.5 degree) were similar to those of humans; those of the other monkey were larger (5.8 degrees). We recorded from V1 neurons in these monkeys while they were performing the orientation discrimination with the same stimuli and under the same conditions as used in the behavioral testing. In order to determine how small a difference in orientation the V1 neurons can, in these conditions, signal reliably by small changes in firing rate, we performed 2 different receiver-operating characteristic (ROC) analyses. One ROC analysis was performed on the number of spikes evoked by the first of the 2 stimulus presentations as a function of the orientation of this stimulus. Neural JNDs derived from the neurometric curve were obtained in this way for 50 cells. In the second ROC analysis, the difference in the number of spikes evoked by the 2 stimuli presented in succession during 1 trial was analyzed as a function of orientation difference between the 2 stimuli. Neural JNDs were obtained by this procedure for 21 cells. These 2 complementary ROC analyses yielded very similar results. Also, the results were similar for the 2 monkeys. A minor fraction of V1 cells can reliably signal difference in orientation as small as 2.5 degrees, but none could signal differences smaller than 2 degrees. Our results also showed that the neural JND obtained by the ROC analysis depends on the duration of the interval during which spikes are counted. In these experiments, this duration could be chosen rather precisely, because the reaction times of the 2 monkeys were measured. Also, our results showed that the neural JND depends on the point of the tuning curve at which the measurement is made and is smallest when this is done on the steepest part of the tuning curve. Finally, our results show that the discriminative capacity of V1 neurons does not depend so much on each of the tuning characteristics--bandwidth, response strength, and variability--as on the combination of these factors.

Mechanisms of Contour Perception in Monkey Visual Cortex. II. Contours Bridging Gaps

Article

Full-text available

Jun 1989

We have studied the mechanism of contour perception by recording from neurons in the visual cortex of alert rhesus monkeys. We used stimuli in which human observers perceive anomalous contours: A moving pair of notches in 2 bright rectangles mimicked an overlaying dark bar. For control, the notches were closed by thin lines so that the anomalous contours disappeared or half of the figure was blanked, with a similar effect. Orientation-selective neurons were studied. With the receptive fields centered in the gap, 23 of 72 (32%) neurons tested in area V2 responded to the moving "bar" even though the stimulus spared their response fields, and when the notches were closed, their responses were reduced or abolished. Likewise, when half of the figure was removed, the neurons usually failed to respond. Neurons with receptive fields within 4 degrees of the fovea signaled anomalous contours bridging gaps of 1 degree-3.5 degrees. The anomalous-contour responses were compared quantitatively with response field profiles and length-summation curves and found to exceed the predictions by linear-summation and summation-to-threshold models. Summation models also fail to explain the effect of closing lines which add only negligible amounts of light. In V1, only one of 26 neurons tested showed comparable responses, and only with a narrow gap. The others responded only when the stimulus invaded the response field and did not show the effect of closing lines, or failed to respond at all. The contour responses in V2, the nonadditivity, and the effect of closure can be explained by the previously proposed model (Peterhans et al., 1986), assuming that the corners excite end-stopped fields orthogonal to the contour whose signals are pooled in the contour neurons.

Mechanisms of contour perception in monkey visual cortex. I. Lines of pattern discontinuity

Article

Full-text available

Jun 1989

We have studied the mechanism of contour perception by recording from neurons in the visual cortex of alert rhesus monkeys. In order to assess the relationship between neural signals and perception, we compared the responses to edges and lines with the responses to patterns in which human observers perceive a contour where no line or edge is given (anomalous contour), such as the border between gratings of thin lines offset by half a cycle. With only one exception out of 60, orientation-selective neurons in area V1 did not signal the anomalous contour. Many neurons failed to respond to this stimulus at all, others responded according to the orientation of the grating lines. In area V2, 45 of 103 neurons (44%) signaled the orientation of the anomalous contour. Sixteen did so without signaling the orientation of the inducing lines. Some responded better to anomalous contours than to the optimum bars or edges. Preferred orientations and widths of tuning for anomalous contour and bar or edge were found to be highly correlated, but not identical, in each neuron. Similar to perception, the neuronal responses depended on a minimum number of lines inducing the contour, but not so much on line spacing, and tended to be weaker when the lines were oblique rather than orthogonal to the border. With oblique lines, the orientations signaled were biased towards the orientation orthogonal to the lines, as in the Zöllner illusion. We conclude that contours may be defined first at the level of V2. While the unresponsiveness of neurons in V1 to this type of anomalous contour is in agreement with linear filter predictions, the responses of V2 neurons need to be explained. We assume that they sum the signals of 2 parallel paths, one that defines edges and lines and another that defines anomalous contours by pooling signals from end-stopped receptive fields oriented mainly orthogonal to the contour.

Response latencies of visual cells in macaque areas V1, V2 and V5

Article

Full-text available

Aug 1989
BRAIN RES

The response to moving light and dark slits was recorded from a total of 94 cells in V1, V2, and V5 (MT) in 9 anesthetized and paralyzed macaque monkeys (M. fascicularis). Using the spatial lag method2, response latencies were calculated for each cell. We obtained median latencies of 85, 96, and 94 ms for cells in areas V1, V2, and V5, respectively. The higher median latencies of V2 and V5 cells compared to V1 are commensurate with later stages of information processing, and are predictable from the anatomy of the interconnections. In addition, a distinct, second population of high-latency cells is present in all 3 regions, but is most abundant in lamina 4 of V5. These may represent either external feedback from other regions or ongoing processing. Extensive overlap of latencies in all 3 regions at both the high and low ends of their respective ranges indicates a considerable degree of parallel interaction between striate and extrastriate cortex.

The organization of chromatic and spatial interactions in the primate striate cortex

Article

Full-text available

Jun 1988

The cytochrome oxidase-rich patches or blobs of the monkey striate cortex have been shown to contain cells that have unoriented receptive fields, many of which are color selective. We studied the functional organization of color opponency in the blob regions of the parafoveal representation of the visual cortex. We also examined the patterns of connectivity among blob and nonblob cells by multiple electrode penetrations and cross-correlation analysis. Some of the color-selective cells in the blobs exhibited receptive fields that were similar to those found in the parvocellular layers of the lateral geniculate nucleus (LGN): one type exhibited center-surround spatial and chromatic opponency corresponding to the Type I cell found in the LGN; another had center-only chromatic opponency, corresponding to the Type II cell of the LGN. A blob color-selective cell with no LGN counterpart had center color opponency with a nonchromatically opponent surround antagonism. We termed this cell the "modified Type II" cell. Contrary to previous reports, few true double color-opponent cells were found. Some blob cells previously characterized as double opponent probably belong to our modified Type II category and, unlike true double opponent cells, do not respond well to isoluminant color boundaries. Occasional color-selective oriented cells were either intermixed or in close proximity to blob cells. Neighboring electrode penetrations within the same blob yielded cells of the same color opponency, either red versus green or blue versus yellow, suggesting that individual blobs are dedicated to processing one color opponency. Blobs dedicated to red/green color opponency were 3 times more numerous than blue/yellow blobs. Furthermore, the cells in layer 4C lying beneath blobs of a given color opponency had identical color opponency to the overlying cells in blobs. Cross-correlation analysis of pairs of nonblob, oriented cells in the superficial layers showed interactions between cells with matched orientation and eye preference, at varying horizontal separations. Such interactions are consistent with anatomically demonstrated clustered horizontal connections. Positive cross-correlograms were found between blob cells in the same and in adjacent blobs when the cells' receptive field type, color opponency, and ocular dominance matched. Correlograms also indicated monosynaptic connections from Type II to modified Type II cells of the same color opponency, suggesting that Type II cells may contribute to the construction of the modified Type II fields in the cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

The suppressive influence of moving textured background on responses of cat striate neurons

Article

Full-text available

Jul 1987

The suppressive action of a moving textured background on responses to moving bars was investigated in 118 striate neurons, 19 dorsal lateral geniculate neurons, and 5 perigeniculate neurons in paralyzed and anesthetized cats. In standard conditions the background was a two-dimensional (2D) noise pattern, the bar moved at optimal speed, and its contrast level was adjusted to yield 50% of the maximum response. Neuronal responses to the moving bar were suppressed when the background moved at the same speed or faster than the bar. The direction of motion of the bar had little influence. This suppressive effect was equally strong in all three experimental samples. The suppressive effect of the moving background was uniformly distributed among the cortical population, being equally strong in all layers, in all parts of the visual field representation, and for different categories of cortical cells. The suppressive effect of the moving background depended little on the structure of the background or on the speed of the bar. The suppression increased with decreasing contrast of the bar. Many (80%) cortical cells and all geniculate neurons responded to the movement of the 2D noise on its own. Most of these cells responded to isolated features ("grains") in the pattern rather than to movement of the whole pattern. There was no difference in strength of suppression between cortical neurons responsive and unresponsive to the moving 2D noise. The possible origins of this suppressive influence of moving backgrounds and its significance for the processing of visual scenes, more complicated than a single stimulus, are discussed.

Endstopped neurons in the visual cortex as a substrate for calculating curvature

Article

Full-text available

Oct 1987

Neurons in the visual cortex typically respond selectively to the orientation, and velocity and direction of movement, of moving-bar stimuli. These responses are generally thought to provide information about the orientation and position of lines and edges in the visual field. Some cells are also endstopped, that is selective for bars of specific lengths. Hubel and Wiesel first observed that endstopped hypercomplex cells could respond to curved stimuli and suggested they might be involved in detection of curvature, but the exact relationship between endstopping and curvature has never been determined. We present here a mathematical model relating endstopping to curvature in which the difference in response of two simple cells gives rise to endstopping and varies in proportion to curvature. We also provide physiological evidence that endstopped cells in area 17 of the cat visual cortex are selective for curvature, whereas non-endstopped cells are not, and that some are selective for the sign of curvature. The prevailing view of edge and curve determination is that orientations are selected locally by the class of simple cortical cells and then integrated to form global curves. We have developed a computational theory of orientation selection which shows that measurements of orientation obtained by simple cells are not sufficient because there will be strong, incorrect responses from cells whose receptive fields (RFs) span distinct curves (Fig. 1). If estimates of curvature are available, however, these inappropriate responses can be eliminated. Curvature provides the key to structuring the network that underlies our theory and distinguishes it from previous lateral inhibition schemes.

Relationships between horizontal interactions and functional architecture in cat striate cortex as revealed by cross-correlation analysis

Article

Full-text available

May 1986

Anatomical studies in the visual cortex have shown the presence of long-range horizontal connections with clustered axonal collaterals, suggesting interactions over distances of several millimeters. We used cross-correlation analysis in cat striate cortex to detect interactions between cells over comparable distances. Using one cell as a reference, we recorded from other cells with a second electrode at varying distances and looked for correlated firing between the two recording sites. This technique allowed us to combine a physiological measure of the strength and type of connection between cells with a characterization of their receptive field properties. The observed interactions were excitatory, and extended over horizontal distances of several millimeters. Furthermore, the interactions were between orientation columns of like specificity, resulting in a waxing and waning in the strength of interaction as the electrodes passed through different orientation columns. We studied relationships between strength of correlation and other receptive field properties and found a tendency for facilitatory interactions between cells sharing the same eye preference. A large proportion of our correlations was due to common input. This feature, and the similarity of interactions between cells in the same column with the reference cell, suggest a high degree of interconnectivity between and within the columns. As the distance between the two electrodes increased, the overlap of the receptive fields of the cells participating in the interactions gradually diminished. At the furthest distances recorded, the cell pairs had nonoverlapping receptive fields separated by several degrees. The distribution and range of these interactions corresponded to the clustering and extent of the horizontal connections observed anatomically.

Synaptic targets of HRP-filled layer III pyramidal cells in the cat striate cortex

Article

Full-text available

Feb 1986

There are numerous hypotheses for the role of the axon collaterals of pyramidal cells. Most hypotheses predict that pyramidal cells activate specific classes of postsynaptic cells. We have studied the postsynaptic targets of two layer III pyramidal cells, that were of special interest because of their clumped axon arborization near, and also 0.4-1.0 mm from the cell body, in register in both layers III and V. 191 terminations from four sites (layers III and V, both in the column of the cell and in distant clumps) were analysed by electron microscopy. Only one bouton contacted a cell body and that was immunoreactive for GABA. The major targets were dendritic spines (84 and 87%), and the remainder were dendritic shafts. Of these 13 were classed as pyramidal-like (P), 8 smooth cell-like (S) and three could not be classified. Four of five S types, but none of the seven P types tested were immunoreactive for GABA, supporting the fine structural classification. The putative inhibitory cells therefore formed not more than 5% of the postsynaptic targets, and their activation could only take place through the convergence of pyramidal cells onto a select population of GABA cells. The results show that the type of pyramidal cells with clumped axons studied here make contacts predominantly with other pyramidal cells. Thus the primary role of both the intra and intercolumnar collateral systems is the activation of other excitatory cells.

Stimulus Specific Responses from Beyond the Classical Receptive Field: Neurophysiological Mechanisms for Local-Global Comparisons in Visual Neurons

Article

Full-text available

Feb 1985

We perceive the visual world as a unitary whole, yet one of the guiding principles of nearly a half century of neurophysiological research since the early recordings by Hartline (1938) has been that the visual system consists of neurons that are driven by stimulation within small discrete portions of the total visual field. These classical receptive fields (CRFs) have been mapped with the excitatory responses evoked by a flashed or moving stimulus, usually a spot or bar of light. Most of the visual neurons, in turn, are organized in a series of maps of the visual field, at least 10 of which exist in the visual cortex in primates as well as additional topographic representations in the lateral geniculate body, pulvinar and optic tectum (Allman 1977, Newsome & Allman 1980, Allman & Kaas 1984). It has been widely assumed that perceptual functions that require the integration of inputs over large portions of the visual field must be either collective properties of arrays of neurons representing the visual field, or features of those neurons at the highest processing levels in the visual system, such as the cells in inferotemporal or posterior parietal cortex that typically possess very large receptive fields and do not appear to be organized in visuotopic maps. These assumptions have been based on the results of the many studies in which receptive fields were mapped with conventional stimuli, presented one at a time, against a featureless background. However, unlike the neurophysiologist's tangent screen, the natural visual scene is rich in features, and there is a growing body of evidence that in many visual neurons stimuli presented outside the CRF strongly and selectively influence neural responses to stimuli presented within the CRF. These results suggest obvious mechanisms for local-global comparisons within visuotopically organized structures. Such broad and specific surround mechanisms could participate in many functions that require the integration of inputs over wide regions of the visual space such as the perceptual constancies, the segregation of figure from ground, and depth perception through motion parallax. In the first section of this paper, we trace the historical development of the evidence of response selectivity for visual stimuli presented beyond the CRF; in the second, examine the anatomical pathways that sub serve these far-reaching surround mechanisms; and in the third, explore the possible relationships between these mechanisms and perception.

Direction- and Velocity-Specific Responses from beyond the Classical Receptive Field in the Middle Temporal Visual Area (MT)

Article

Full-text available

Feb 1985

The true receptive field of more than 90% of neurons in the middle temporal visual area (MT) extends well beyond the classical receptive field (crf), as mapped with conventional bar or spot stimuli, and includes a surrounding region that is 50 to 100 times the area of the crf. These extensive surrounds are demonstrated by simultaneously stimulating the crf and the surround with moving stimuli. The surrounds commonly have directional and velocity-selective influences that are antagonistic to the response from the crf. The crfs of MT neurons are organized in a topographic representation of the visual field. Thus MT neurons are embedded in an orderly visuotopic array, but are capable of integrating local stimulus conditions within a global context. The extensive surrounds of MT neurons may be involved in figure-ground discrimination, preattentive vision, perceptual constancies, and depth perception through motion cues.

Intrinsic laminar lattice connections in primate visual cortex

Article

May 1983
J COMP NEUROL

Intracortical injections of horseradish peroxidase (HRP) reveal a system of periodically organized intrinsic connections in primate striate cortex. In layers 2 and 3 these connections form a reticular or latticelike pattern, extending for about 1.5–2.0 mm around an injection. This connectional lattice is composed of HRP-labeled walls (350–450 μm apart in Saimiri and about 500–600 μm in macaque) surrounding unlabeled central lacunae. Within the lattice walls there are regularly arranged punctate loci of particularly dense HRP label, appearing as isolated patches as the lattice wall labeling thins further from the injection site. A periodic organization has also been demonstrated for the intrinsic connections in layer 4B, which are apparently in register with the supragranular periodicities, although separated from these by a thin unlabeled region. The 4B lattice is particularly prominent in squirrel monkey, extending for 2–3 mm from an injection. In both layers, these intrinsic connections are demonstrated by orthogradely and retrogradely transported HRP and seem to reflect a system of neurons with long horizontal axon collaterals, presumably with arborizations at regularly spaced intervals. The intrinsic connectional lattice in layers 2 and 3 resembles the repetitive array of cytochrome oxidase activity in these layers; but despite similarities of dimension and pattern, the two systems do not appear identical. In primate, as previously described in tree shrews (Rockland et al., 1982), the HRP-labeled anatomical connections resemble the pattern of 2-deoxy-glucose accumulation resulting from stimulation with oriented lines, although the functional importance of these connections remains obscure.

Differential responses of cat visual cortical cells to textured stimuli

Article

Apr 1975

The responsiveness of primary visual cortical units to luminance edges or bars (Hubel and Wiesel, 1962) has encouraged the belief that they may serve as the elementary edge- or bar-'detectors' in a hierarchic pattern-recognition process. One possible objection to this view is that patterns can readily be reeognised when presented against a background of the same average luminance but different texture. Even an area of static visual 'noise' identieM in texture to its background, which is completely camouflaged when at rest, has its contours instantly recognizable if moved relative to the background. It might be felt that this objection would be answered if the same units proved sensitive to such 'kinetic contours' as well as to contours of luminance. We have compared the responses of a number of 'simple', 'complex' and 'hypercomplex' cells in eat visual area 17 to conventional flashed and moving bar stimuli on the one hand, and various patterns of static visual 'noise' (MacKay, 1965) and regular textured arrays on the other. We found no support for the idea that simple or complex cells might be sensitive to kinetic as well as to luminance contours as such; but their responses to noise stimuli showed interesting systematic differences that may throw further light on their respective functions. Single cells were recorded with low-impedance 4M-NaC1 micropipettcs from visual cortical area 17 of four adult eats. Receptive fields lay on or near the vertical meridian, centred 3--8 ~ below the areae centrales. Animals were prepared under halothane anaesthesia, then maintained under 80~o :20~ N20/O 2 supplemented with small doses (averaging 1.0 mg. kg -1. hr -1) of pentobarbitone as required to stabilise the EEG. Blood pressure and pulse, gas exchange and rectal temperature were also monitored. Throughout recordings animals were paralysed with a continuous i.v. infusion of Flaxedil (May and Baker; 7--10 mg. kg-l. hr -1) in 2.5~o dextrose, and ventilated at 28 strokes/min to a steady 4~o end-tidal CO s. Pupils were dilated and nictitating membranes retracted pharmacologically. Neutral contact lenses and 5 mm diameter artificial pupils were used routinely and trial lenses, selected retinoseopically, provided the appropriate spherical correction for the various stimulus distances used. Locations of optic discs and areae centrales were monitored by back-projection with an ophthalmoscope and cube corner prism, or according to the method of Fernald and Chase (1971). Background

The effects of concentrated and distributed attention on peripheral acuity

Article

Jun 1973

Two experiments studied the peripheral discriminability of a target differing in its line slope (a tilted T) and in its line arrangement (an L) when presented in briefly flashed displays of upright Ts. The results showed that: (a) an L and a tilted T were equal in discriminability when attention was focused or concentrated on one display position, (b) the discriminability of an L decreased while the discriminability of a tilted T was not statistically significantly affected as the number of display positions that attention needed to be paid to increased, and (c) the reaction time to find a disparate tilted T was less than that to find a disparate L. The results are interpreted as supporting the hypothesis that, under distributed attention in peripheral vision, the visual system is more sensitive to differences in line slope than to differences in line arrangement The results are discussed in connection with hypotheses of how selective attention affects the discriminability of a target.

The shift-effect in the lateral geniculate body of the rhesus monkey

Article

Oct 1977

J Krüger

Responses to sudden shifts of a pattern far away from the receptive field (shift-effect) were found in 73 out of 81 cells of the ventral, magnocellular LGN layers, but in only 26 out of 85 cells of the dorsal, parvocellular layers. Most of the former responses were clear and excitatory, and most of the latter were weak and inhibitory. Excitatory responses were stronger for steady receptive field illumination which when turned on also yielded an excitation. No convincing dependence on the colour of the receptive field illumination was observed. The results are discussed with respect to the hypothesis of transmission of steady illumination via the shift-effect ("restoration"), and with respect to a hypothesis assigning a signaling function of low stimulus specificity to the ventral layers.

Dimensions and Properties of End-zone Inhibitory Areas in Receptive Fields of Hypercomplex Cells in Cat Striate Cortex

Article

Jun 1979

Subregions in the receptive fields of hypercomplex cells have been examined by a variety of quantitative methods with particular reference to the dimensions and properties of the end-zone inhibitory areas. These data have made it possible to construct detailed maps of the receptive-field organization of the two types of hypercomplex cell (I and II). The spatial extent of the end-zone inhibitory area is much greater than that responsible for discharge-region excitation. End-zone inhibition is, however, position dependent, the part of the area causing maximal inhibition lying precisely along the line of the most responsive part of the discharge region and just beyond its lateral border. Spatial summation of end-zone inhibition takes place along the line of its optimal stimulus orientation. Some simple and complex cells may have hypercomplex-type length-response curves in the nonpreferred direction of stimulus movement and vice versa for some hypercomplex cells. Whether these response patterns are due to the presence of direction-selective end-zone inhibition or not remains to be determined. While end-zone inhibition may be direction selective, it appears that it is usually nondirectional. Even when discharge region excitation is itself completely direction selective, the end-zone inhibition may be equally effective in both directions. Hence end-zone inhibition appears to be independent of the mechanism responsible for the direction selectivity of the discharge region. End-zone inhibition is stimulus orientation dependent, being maximal when the orientation is the same as the orientation that is optimal for the discharge region. When the stimulus is rotated away from the optimal, the strength of the inhibition progressively declines, falling to zero at 90° to the optimal. This property distinguishes end-zone inhibition from side band inhibition since the latter is not orientation sensitive. There may be considerable, or even total, spatial overlap between discharge-region excitation and end-zone inhibition, the spatial summation required for excitation being much less that that required to produce an inhibitory effect. The onset of inhibition on the length-response curve indicates that the effects of the spatial summation of inhibition now exceeds those of discharge-region excitation.

Effects of interacting visual patterns on single cell responses in cat's striate cortex

Article

Feb 1977
VISION RES

Extracellular records were taken from single units in area 17 of anaesthetized and immobilized cats. The excitatory part of the receptive field of each unit (ERF or RF centre) was stimulated with an optimally orientated contrast. Stimulating the surrounding area with a grating revealed three types of centre-surround interaction.(1)In one group of cells, the centre response was maximally suppressed when the surround grating had the same orientation as the centre stimulus. The suppression gradually decreased as the grating was rotated away from this optimal orientation. The inhibitory area in the orientation domain resembled that of an inverted orientation tuning curve. The suppression also depended on the direction in which the surround grating was moved. These cells were identified as simple cells.(2)In other cells, the centre response was suppressed regardless of orientation and movement direction of the surround grating. These were simple cells too.(3)In a third group of cells, the centre response remained unchanged when the surround was stimulated whatever the orientation or direction of movement of the grating. These cells were identified as complex cells.It was found that for the most part the orientation specific suppression of the centre response arose from specific areas which corresponded roughly to the inhibitory sidebands described by Henry and Bishop (1971). Some suppression might also be elicited from areas which lie outside the classical RF-area. That is, the interaction seen in the first group of cells depended on the position as well as the orientation of the surround grating. Possible mechanisms of the surround-inhibition are discussed.

Differential responsiveness of simple and complex cells in cat striate cortex to visual texture

Article

Dec 1977

The responsiveness of 254 simple and complex striate cortical cells to various forms of static and dynamic textured visual stimuli was studied in cats, lightly anaesthetised with N2O/O2 mixtures supplemented with pentobarbitone.

Orientation-selective inhibition from beyond the classic visual receptive field

Article

Feb 1978
BRAIN RES

The origin of efferent pathways from the primary visual cortex, area 17, of the macaque monkey as shown by retrograde transport of horseradish peroxidase

Article

Dec 1975

The retrograde transport of horseradish peroxidase has been used to identify efferent cells in area 17 of the macaque. Cells projecting to the lateral geniculate nucleus are small to medium sized pyramidal neurons with somata in lamina 6 and the adjacent white matter. The projection to the parvocellular division arises preferentially from the upper half of lamina 6, while that to the magnocellular division arises preferentially from the lower part of the lamina. The projection to both superior colliculus and inferior pulvinar arises from all sizes of pyramidal neurons lying in lamina 5B (Lund and Boothe, '75); at least the largest pyramidal neurons of lamina 5B send collateral axon branches to both destinations. Injections with extensive spread of horseradish peroxidase show that many cells of lamina 4B and the large pyramidal neurons of upper lamina 6 also project extrinsically but their terminal sites have not been identified. Other studies have indicated that cells of laminae 2 and 3 project to areas 18 and 19. Therefore every lamina of the visual cortex, with the exception of those receiving a direct thalamic input, contains cells projecting extrinsically. Further, each lamina projects to a different destination and from Golgi studies can be shown to contain cells with specific patterns of dendritic branching which relate to the distribution of thalamic afferents and to the patterns of intracortical connections. These findings emphasise the significance of the horizontal organisation of the cortex with relation to the flow of information through it and contrast with the current concept of columnar organisation shown in physiological studies.

Binocular-disparity-dependent upper-lower hemifield anisotropy and left-right hemifield isotropy as revealed by dynamic random-dot stereograms

Article

Feb 1976

Dynamic random-dot stereograms devoid of all monocular depth cues were used to measure the limits of temporal and spatial resolution in the center of the visual field. The temporal durations for detecting a small, briefly presented test square of different binocular disparity than the surround varied as a function of its location and binocular disparity. The test squares presented in the upper hemifield were detectable at consistently shorter durations than those presented in the lower hemifield for a surround disparity which was uncrossed relative to the fixation marker. For crossed surround disparity this preference reversed, resulting in a superiority of the lower hemifield. The anisotropy diminished for zero surround disparity. No such anisotropy was found when left and right visual hemifields were compared. It was also shown that this upper-lower temporal anisotropy (and left-right isotropy) is paralleled by a similar disparity-dependent upper-lower anistropy (and left-right isotropy) in spatial resolution. Introduction of monocular clues into the stereograms tended to eliminate the anisotropies. This implies that the anisotropies reflect the spatiotemporal properties and distribution of binocular disparity detectors in the human cortex and result in a tilted surface that pivots around the horizontal midline in the space of binocular depth perception.

Targets of horizontal connections in macaque primary visual cortex

Article

Mar 1991

Pyramidal neurons within the cerebral cortex are known to make long-range horizontal connections via an extensive axonal collateral system. The synaptic characteristics and specificities of these connections were studied at the ultrastructural level. Two superficial layer pyramidal cells in the primate striate cortex were labeled by intracellular injections with horseradish peroxidase (HRP) and their axon terminals were subsequently examined with the technique of electron microscopic (EM) serial reconstruction. At the light microscopic level both cells showed the characteristic pattern of widespread, clustered axon collaterals. We examined collateral clusters located near the dendritic field (proximal) and approximately 0.5 mm away (distal). The synapses were of the asymmetric/round vesicle variety (type I), and were therefore presumably excitatory. Three-quarters of the postsynaptic targets were the dendritic spines of other pyramidal cells. A few of the axodendritic synapses were with the shafts of pyramidal cells, bringing the proportion of pyramidal cell targets to 80%. The remaining labeled endings were made with the dendritic shafts of smooth stellate cells, which are presumed to be (GABA)ergic inhibitory cells. On the basis of serial reconstruction of a few of these cells and their dendrites, a likely candidate for one target inhibitory cell is the small-medium basket cell. Taken together, this pattern of outputs suggests a mixture of postsynaptic effects mediated by consequence the horizontal connections may well be the substrate for the variety of influences observed between the receptive field center and its surround.

Influences of uniform and textured backgrounds on the impulse activity of neurons in area V1 of the alert macaque

Article

Jan 1991
BRAIN RES

The influences of the visual background on the spontaneous and evoked activity of neurons in the striate cortex (V1) of the awake and behaving macaque were investigated using uniform (dark and bright) and textured (dynamic random-dot) large fields (10 degrees) centered on the receptive field of the cell under study. Rhesus monkeys were trained to fixate a small target while visual patterns were presented on monitor displays and the impulse activity of single cortical neurons recorded extracellularly with metal microelectrodes. The discharge rates of the ongoing, spontaneous activity of the vast majority of V1 neurons, as well as their responses to optimally adjusted bar stimuli, were not significantly influenced by the luminance of a uniform background. On the other hand, the activity of more than 50% of V1 neurons was clearly affected by a textured background. Comparison of the effects of a uniformly dark background and a background of dynamic random dots showed that the neuron's spontaneous discharge rate was typically higher in the presence of the textured background, while the evoked response was often reduced in amplitude or even suppressed. The opposite effects were observed in only a few neurons. These findings indicate that neurons in area V1 are highly sensitive to a textured background of dynamic random dots which exert on them an activating effect, chiefly by stimulation of the neuron's receptive field, with consequent increase in the ongoing discharge and a reduction of the dynamic range of impulse activity, leading to a reduction in the amplitude of the response evoked by a contrast stimulus.

The influence of contextual stimuli on the orientation selectivity of cells in primary visual cortex of the cat

Article

Feb 1990
VISION RES

Perception of a visual attribute, such as orientation, is strongly dependent on the context within which a feature is presented, such as that seen in the tilt illusion. The possibility that the neurophysiological basis for this phenomenon may be manifest at the level of cells in striate cortex is suggested by anatomical and physiological observations of orientation dependent long range horizontal connections which relate disparate points in the visual field. This study explores the dependency of the functional properties of single cells on visual context. We observed several influences of the visual field area surrounding cells' receptive field on the properties of the receptive field center: inhibition or facilitation dependent on the orientation of the surround, shifts in orientation preference and changes in the bandwidth of orientation tuning. To relate these changes to perceptual changes in orientation we modeled a neuronal ensemble encoding orientation. Our results show that the filter characteristics of striate cortical cells are not necessarily fixed, but can be dynamic, changing according to context.

Local circuit neurons of macaque monkey striate cortex: II. Neurons of laminae 5B and 6

Article

Oct 1988

This study investigates the intrinsic organization of axons and dendrites of aspinous, local circuit neurons of the macaque monkey visual striate cortex. These investigations use Golgi Rapid preparations of cortical tissue from monkey aged 3 weeks postnatal to adult. We have earlier (Lund, '87) described local circuit neurons found within laminae 5A and 4C; this present account is of neurons found in the infragranular laminae 5B and 6. Since the majority of such neurons are GABAergic and therefore believed to be inhibitory, their role in laminae 5B and 6, the principal sources of efferent projections to subcortical regions, is of considerable importance. We find laminae 5B and 6 to have in common at least one general class of local circuit neuron-the "basket" neuron. However, a major difference is seen in the axonal projections to the superficial layers made by these and other local circuit neurons in the two laminae; lamina 5B has local circuit neurons with principal rising axon projections to lamina 2/3A, areas whereas lamina 6 has local circuit neurons with principal rising axon projections to divisions of 4C, 4A, and 3B. These local circuit neuron axon projections mimic the different patterns of apical dendritic and recurrent axon projections of pyramidal neurons lying within laminae 5B and 6, which are linked together by both dendritic and axonal arbors of local circuit neurons in their neuropils extending between the two laminae. The border zone between 5B and 6 is a specialized region with its own variety of horizontally oriented local circuit neurons, and it also serves as a special focus for pericellular axon arrays from a particular variety of local circuit neuron lying within lamina 6. These pericellular axon "baskets" surround the somata and initial dendritic segments of the largest pyramidal neurons of layer 6, which are known to project both to cortical area MT (V5) and to the superior colliculus (Fries et al., '85). Many of the local circuit neurons of layer 5B send axon trunks into the white matter, and we therefore, suspect them of providing efferent projections. The axons of lamina 6 local circuit neurons have not been found to make such clear-cut contributions to the white matter.

Short-range limitation on detection of feature differences

Article

Feb 1987

We studied the ability of observers to detect the presence of a clearly visible line segment against a background of line segments of different orientation. As we increase the number (density) of these background lines, we find that detectability does not behave monotonically. Adding a small number of background lines decreases detectability but if adjacent line segments are permitted to fall in close range, a further increase of background lines improves performance which eventually reaches a constant level. This suggests that detection of feature differences involves a short-range process. The range of this process is about two degrees or twice the length of the line segments used. Thus texture-gradients between different elements are only formed if the distance between these elements is not much larger than the average element size.

Connections between pyramidal neurons in layer 5 of cat visual cortex (area 17)

Article

May 1987

The structural features of two physiologically‐characterised pyramidal neurons (PC 1 and PC 2 ) closely situated in layer 5b in the visual cortex (area 17) of a single cat were studied using a combination of electrophysiological and anatomical techniques. Both PC 1 and PC 2 had exceptionally large somata (30–40 μm in diameter). On the basis of this and other morphological features cell PC 1 was classified as a Meynert cell. PC 1 possessed a very large (2.75° × 4.50°) binocularly driven standard complex receptive field. PC 2 was also binocularly driven with a small, B‐type receptive field. Both cells had the same preference for the direction and orientation of visual stimuli. PC 1 and PC 2 could be antidromically activated from stimulating electrodes positioned above the dorsal lateral geniculate nucleus with a response latency indicating that these cells probably innervated the visual tectum or pretectum. In addition to corticoefferent axons, the two neurons possessed extensive intracortical axon arbors that ramified extensively in layers 5 and 6 of the medial and lateral banks of the lateral gyrus in area 17. Axon collaterals from both PC 1 and PC 2 also innervated a small common target region in area 18. A total of 313 boutons from the axonal arbors of PC 1 and PC 2 were examined in the electron microscope. All of the identified synaptic junctions were found to establish Gray type 1 asymmetrical contacts. The combined ultrastructural data for both neurons indicated that 80% of boutons were onto dendritic spine heads, with 14%, 6%, and 1% onto small‐, medium‐, and large‐calibre dendritic shafts, respectively. The spectrum of postsynaptic targets showed little variation with respect to lamina, distance from somata, or cortical area. Other large pyramidal neurons in layer 5 and spiny neurons in layer 6 were identified as receiving synaptic input from either PC 1 or PC 2 . Using a computer graphics system, rotations of the bouton distributions revealed the existence of a clustered innervation of layers 5 and 6 in areas 17 and 18 derived from the two identified neurons. The bouton distributions strongly resembled the tangential pattern described previously for the functional slab‐like organisation of the cortex. The results provide a morphological basis for the clustered intrinsic connectivity of pyramidal cells in layers 5 and 6 of the cat visual cortex. Furthermore, the results indicate the widespread excitatory influence of large pyramidal neurons on other cells projecting subcortically to sites dealing with visually guided behavior.

Sensitivity for structure gradient in texture discrimination tasks

Article

Feb 1985
VISION RES

Hans-Christoph Nothdurft

Recent experiments indicate that the segregation of visual structures ("texture discrimination") depends not only on the form of texture elements but also on their spacing. Structures with discriminable elements in close proximity can be segregated more easily than patterns in which the same texture elements are more widely spaced. In dot arrays with areas of different dot luminance, segregation was found to depend on both the luminance difference and dot spacing; discrimination of texture areas in coarse dot rasters required greater differences in luminance than in fine rasters. Also, in regular arrays of iso-luminant line patterns, the maximal spacing between neighbouring lines for which different texture areas could still be discriminated was found to be influenced by the degree of dissimilarity between elements. For lines of a given length, texture areas with small differences in orientation became indiscriminable at smaller spacings than texture areas with orthogonal line orientations. Line length additionally had a strong effect on texture discrimination; increasing the line length for a given spacing provided easier segregation of texture areas. However, over a range of raster widths, discrimination of texture areas with a given difference in line orientation varied not with absolute values of line length but with the ratio of line length to interline spacing. Overall, the data suggest that texture discrimination in man is based on the evaluation of variation in structure over space (defined as the "texture gradient"). If local variation of structure is too small, texture areas cannot be discriminated, though differences between texture elements themselves may be apparent. As far as the dependence on variation over space is concerned, discrimination of iso-luminant textures resembles the limited sensitivity of the visual system for differences in texture luminance.

Shifts in Selective Visual Attention: Towards the Underlying Neural Circuitry

Article

Feb 1985
Hum Neurobiol

Psychophysical and physiological evidence indicates that the visual system of primates and humans has evolved a specialized processing focus moving across the visual scene. This study addresses the question of how simple networks of neuron-like elements can account for a variety of phenomena associated with this shift of selective visual attention. Specifically, we propose the following: (1) A number of elementary features, such as color, orientation, direction of movement, disparity etc. are represented in parallel in different topographical maps, called the early representation. (2) There exists a selective mapping from the early topographic representation into a more central non-topographic representation, such that at any instant the central representation contains the properties of only a single location in the visual scene, the selected location. We suggest that this mapping is the principal expression of early selective visual attention. One function of selective attention is to fuse information from different maps into one coherent whole. (3) Certain selection rules determine which locations will be mapped into the central representation. The major rule, using the conspicuity of locations in the early representation, is implemented using a so-called Winner-Take-All network. Inhibiting the selected location in this network causes an automatic shift towards the next most conspicious location. Additional rules are proximity and similarity preferences. We discuss how these rules can be implemented in neuron-like networks and suggest a possible role for the extensive back-projection from the visual cortex to the LGN.

Texture discrimination: Representation of orientation and luminance differences in cells of the cat striate cortex

Article

Feb 1985
VISION RES

Neuronal texture discrimination in the cat striate cortex was investigated by measuring the responses of single cells to different pattern structures. The representation of two independent features, texture orientation and texture luminance, was analysed in detail and the sensitivity of neurones to either feature was studied at different levels of structure density. Texture patterns were systematically moved across the receptive field. From the cell response to various parts of the pattern, "response patterns" were generated which displayed the cell transform of the textured stimulus pattern. Only when texture structures were coarse, were cells able to encode the texture orientation of an area. Differences in texture luminance, on the other hand, were detected only in fine texture structures. Further, these textural features were processed in a different manner: Cells responded to differences in texture luminance but continuously to areas of similar texture orientation. Thus, responses of striate cells reveal an ambiguous representation of texture features and a failure to uniquely encode texture borders.

Visual receptive fields of striate cortex neurons in awake monkeys

Article

Oct 1969

R H Wurtz

An accurate and linear infrared oculometer

Article

Oct 1983
J NEUROSCI METH

A method for measuring horizontal and vertical eye movements is described. The oculometer utilize infrared light and resolves 0.1 degree over a linear range of +/- 20 degrees. The simultaneous observation of the fixation target and eye position with an infrared mirror and two television cameras on a single monitor makes the mechanical and electrical calibration very easy. The system has been used successfully in animal studies of vision and eye movements, in particular during recording of single cells in visual brain structures of behaving monkeys.

Representation of spatial details in textured patterns by cells of the cat striate cortex

Article

Feb 1984

The ability of single cells to represent the spatial details of textured stimuli was investigated. Two complementary aspects of cell response were considered, the ability to discriminate fine stimulus details and the property of integration over wider areas of a structure to encode differences in mean luminance. Responses of simple and complex cells were distinct in some respects. Spatial discrimination: Simple cells would encode orientation of line arrays as long as individual line elements could be spatially resolved. By contrast, complex cells were able to distinguish the orientation of texture areas even when the individual lines of the stimulus were not resolved in their response. Threshold sensitivity for texture orientation was of the same order in both cell classes despite differences in receptive field size. Spatial integration: Complex cells responded to texture luminance differences of much coarser patterns than did simple cells. These responses, however, were not biased for contour orientation unless finer patterns were used. Only with very fine textures did responses become indistinguishable from those to uniform stimuli for both simple and complex cells. For complex cells, there was a smooth transition from resolution to fusion of spatial details with increasing structural density. Simple cells were insensitive to both detailed and global properties of a stimulus pattern over a wide range of texture density. Implications for alternative measures of visual acuity of single cells are discussed.

A statistical method for the estimation of neuronal response latency and its functional interpretation

Article

Dec 1983
BRAIN RES

The functional role of many central nervous structures has been inferred from the temporal relationship of a neuronal response with the different sensory and motor events in an experimental design such as when an animal performs a trained movement in response to a conditioned stimulus. However, this kind of data analysis leads to problems in estimating the occurrence and latency of any neuronal response. We examine these problems and propose a novel technique of data analysis to estimate the point of change in a sequence of neuronal discharge. Furthermore, data can be tested to see whether the neuronal response is related to the conditioned stimulus or the motor act. The method can also be used in the simple situation of determining the latency of a neuronal response after a stimulus.

Parallel versus serial processing in rapid pattern discrimination

Article

Jun 1983

When stimuli are available for just a brief period (approximately 100 ms) only restricted spatial information can be processed by the visual system. If the stimuli are presented very briefly, eye movements are not possible. The time during which the after-image of the stimulus is available for inspection is terminated by presentation of a masking pattern. We show here that in these conditions a small pattern is easily detected against a background made up of many others, only if this target pattern differs from the background patterns in certain local features. In this case the detectability of the target is almost independent of the number of background elements, suggesting that a parallel process is operating. Detection of patterns not differing from their backgrounds in such features requires focal attention which is a serial process. The aperture of this attention is scaled to minimize the number of shifts of attention required.

Functional properties of neurons in middle temporal visual area of the macaque monkey. I. Selectivity for stimulus direction, speed, and orientation

Article

Jun 1983

1. Recordings were made from single units in the middle temporal visual area (MT) of anesthetized, paralyzed macaque monkeys. A computer-driven stimulator was used to make quantitative tests of selectivity for stimulus direction, speed, and orientation. The data were taken from 168 units that were histologically identified as being in MT. 2. The results confirm previous reports of a high degree of direction selectivity in MT. The response above background to stimuli moving in a unit's preferred direction was, an average, 10.9 times that to stimuli moving in the opposite direction. There was a marked tendency for nearby units to have similar preferred directions. 3. Most units were also sharply tuned for the speed of stimulus motion. For some cells the response fell to less than half-maximal at speeds only a factor of two from the optimum; on average, responses were greater than half-maximal only over a 7.7-fold range of speed. The distribution of preferred speeds for different units was unimodal, with a peak near 32 degrees/s; the total range of preferred speeds extended from 2 to 256 degrees/s. Nearby units generally responded best to similar speeds of motion. 4. Most units in MT showed selectivity for stimulus orientation when tested with stationary, flashed bars. However, stationary stimuli generally elicited only brief responses; when averaged over the duration of the stimulus, the responses were much less than those to moving stimuli. The preferred orientation was usually, but not always, perpendicular to the preferred direction of movement. 5. A comparison of the results of the present study with a previous quantitative investigation in the owl monkey shows a striking similarity in response properties in MT of the two species. 6. The presence of both direction and speed selectivity in MT of the macaque suggests that this area is more specialized for the analysis of visual motion than has been previously recognized.

Receptive fields of optic tract axons and lateral geniculate cells: Peripheral extent and barbiturate sensitivity

Article

Dec 1964

James T. McIlwain

Receptive Fields and Functional Architecture in Two Nonstriate Visual Areas (18 and 19) of the Cat

Article

Apr 1965

Glass Insulated Platinum Microelectrode

Article

Dec 1960

Microelectrodes for electrophysiological use have been prepared easily and quickly by electrolytically sharpening platinum iridium alloy wire and coating with molten glass. The desirable combination of the electrical characteristics and strength of the platinum iridium wire with the exceptional durability of glass insulation has long been known, but earlier methods of fabrication were difficult and tedious.

end-zone inhibitory areas in receptive fields of hypercomplex cells in cat striate cortex tion in monkey visual cortex. II. Contours bridging gaps

833-849

G A Orban
H Kato
Bishop
E And Peterhans

ORBAN, G. A., KATO, H., AND BISHOP, end-zone inhibitory areas in receptive fields of hypercomplex cells in cat striate cortex. J. Neurophysiol. 42: 833-849, PETERHANS, E. AND VON DER HEYDT, tion in monkey visual cortex. II. Contours bridging gaps. J. Neurosci. 9: 1749-1763, 1989

Orientation-selective beyond the classic visual receptive field Sensitivity for structure gradient in texture discrimina-tion tasks Texture discrimination ulate nucleus

359-365

J I Nelson
B J Frost
H C Nothdurft

NELSON, J. I. AND FROST, B. J. Orientation-selective beyond the classic visual receptive field. Brain Res. 139: 359-365, NOTHDURFT, H. C. Sensitivity for structure gradient in texture discrimina-tion tasks. Vision Res. 25: 1957-1968, NOTHDURFT, H. C. Texture discrimination ulate nucleus. Exp. Brain Res. 82: 48-66, 1990

AND POGGIO, and textured backgrounds on the impulse activity of neurons in area V 1 of the alert macaque A feature-integration theory of atten-tion

26-270

S Squatrito
Y Trotter
A M Treisman
G Gelade

SQUATRITO, S., TROTTER, Y., AND POGGIO, and textured backgrounds on the impulse activity of neurons in area V 1 of the alert macaque. Brain Res. 536: 26 l-270, TREISMAN, A. M. AND GELADE, G. A feature-integration theory of atten-tion. Cognit. Psychol. 12: 97-l 36, 1980

SAGI, unit responses to static and dynamic and V 1 cortex (Abstract)

E Deyoe
J Knierim

DEYOE, E., KNIERIM, J., SAGI, unit responses to static and dynamic and V 1 cortex (Abstract). Invest. Ophthalmol. Vis. Sci. 27 Suppl. : 18, 1986

Spatial organization of suppressive surround effects in neurons of area V 1 in alert macaques

1270

J J Knierim
Van Essen

KNIERIM, J. J. AND VAN ESSEN, D. C. Spatial organization of suppressive surround effects in neurons of area V 1 in alert macaques. Sot. Neurosci. Ahstr. 16: 1270, 1990

Shifts in selective visual attention: towards the underlying neural circuitry The shift-effect in the lateral geniculate body of the rhesus monkey glion cells of the rhesus monkey Local circuit neurons of macaque monkey striate cortex. I. Neurons of lamina 4C and 5A

2-19

C Koch
S Ullman
J Krueger
J Krueger
B Fischer

KOCH, C. AND ULLMAN, S. Shifts in selective visual attention: towards the underlying neural circuitry. Hum. Neurohiol. 4: 2 19-227, KRUEGER, J. The shift-effect in the lateral geniculate body of the rhesus monkey. Exp. Brain Res. 29: 387-392, KRUEGER, J., FISCHER, B., AND BARTH, glion cells of the rhesus monkey. Exp. Brain Res. 23: 443-446, LUND, J. S. Local circuit neurons of macaque monkey striate cortex. I. Neurons of lamina 4C and 5A. J. Comp. Neurol. 257: 60-92, 1987

Neuronal responses to static texture patterns in area V1 of the alert macaque monkey

Abstract

No full-text available

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