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Publications
Publications (49)
Our vision is best only in the center of our gaze, and we use saccadic eye movements to direct gaze to objects and features of interest. We make more than 180,000 saccades per day, and accurate and efficient saccades are crucial for most visuo-motor tasks. Saccades are typically studied using small point stimuli, despite the fact that most real-wor...
It has been suggested that, during difficult visual search tasks involving time pressure and multiple saccades, inhibitory tagging helps to facilitate efficient saccade target selection by reducing responses to objects in the scene once they have been searched and rejected. The superior colliculus (SC) is a midbrain structure involved in target sel...
It has been suggested that, during difficult visual-search tasks involving time pressure and multiple saccades, inhibitory tagging helps to facilitate efficient saccade target selection by inhibiting saccades to objects in the scene once they have been searched and rejected. The superior colliculus (SC) is a midbrain structure that is involved in t...
Inhibitory tagging is an important feature of many models of saccade target selection, in particular those based on the notion of a neural priority map. The superior colliculus (SC) has been suggested as a potential site of such a map, yet it is unknown if inhibitory tagging is represented in the SC during visual search. In this study, we tested th...
Neurons governing saccadic eye movements typically multiplex sensory, cognitive, and movement-related signals. How is a reliable ‘go’ signal extracted from this mixture? A new study reveals that saccade initiation is gated by the temporal stability of rising population activity.
While aiming and shooting, we make tiny eye movements called microsaccades that shift gaze between task-relevant objects within a small region of the visual field. However, in the brief period before pressing the trigger, microsaccades are suppressed. This might be due to the lack of a requirement to shift gaze as the retinal images of the two obje...
Previous studies have shown that the influence of a behaviorally irrelevant distractor on saccade reaction times (SRTs) varies depending on the temporal and spatial relationship between the distractor and the saccade target. We measured distractor influence on SRTs to a subsequently presented target, varying the spatial location and the timing betw...
We recently demonstrated that inactivation of the primate superior colliculus (SC) causes a deficit in target selection for arm-reaching movements when the reach target is located in the inactivated field (Song et al. 2011). This is consistent with the notion that the SC is part of a general-purpose target selection network beyond eye movements. To...
Covert visual search has been studied extensively in humans, and has been used as a tool for understanding visual attention and cueing effects. In contrast, much less is known about covert search performance in monkeys, despite the fact that much of our understanding of the neural mechanisms of attention is based on these animals. In this study, we...
Purposive action requires the selection of a single movement goal from multiple possibilities. Neural structures involved in movement planning and execution often exhibit activity related to target selection. A key question is whether this activity is specific to the type of movement produced by the structure, perhaps consisting of a competition am...
Attending to different stimulus features such as contrast or orientation can change the pattern of neural responses in human V1 measured with fMRI. We show that these pattern changes are much more distinct for colored stimuli than for achromatic stimuli. This is evidence for a classic model of V1 functional architecture in which chromatic contrast...
Prior to the onset of a saccade or a reach, attention is directed to the goal of the upcoming movement. However, it remains unknown whether attentional resources are shared across effectors for simultaneous eye and hand movements. Using a 4-AFC shape discrimination task, we investigated attentional allocation during the planning of a saccade alone,...
Last year, we reported that temporary inactivation of a portion of the superior colliculus (SC) in rhesus monkeys results in a target selection deficit in a color-oddity search task. Specifically, after a microinjection of lidocaine or muscimol into the intermediate layers of the SC, saccades can still be made to visual targets in the affected part...
Attention is directed to the upcoming goal location of both saccades and reaches . It remains unknown however, how attention is allocated during simultaneous eye and hand movements. We investigated attentional allocation through a 4-alternative forced-choice shape discrimination task (Deubel & Schneider, 1996) while subjects made either a saccade o...
The primate superior colliculus (SC) is important for the execution of saccadic eye movements, but recent evidence suggests that it also plays a role in the higher-level process of target selection for saccadic and pursuit eye movements, as well as in covert attention shifts. Thus, we speculated that SC activity may participate in a generalized sal...
Saccades and covert shifts of attention are used to improve perception of peripheral stimuli. The primate superior colliculus (SC) plays a central role in saccades, and recent evidence suggests its involvement in visuo-spatial attention. To test the role of the SC in attention, we recorded single-unit activity as monkeys remained fixated and discri...
The pre-motor theory of attention posits that oculomotor regions like the frontal eye field (FEF) are involved in shifts of attention, as well as eye movements. This idea has gained support from behavioral and neuroimaging studies in humans, as well as from microstimulation and recording experiments in monkeys. We reasoned that if the FEF is involv...
The aim of the current work was to investigate the spatial extent of attentional facilitation and inhibition of return (IOR) in response to an exogenous cue over time. We used saccade latencies as a behavioral correlate of attentional allocation. Two humans and two monkeys made saccades to visual targets at 136 locations spread across the visual fi...
Most visual scenes are complex and crowded, with several different objects competing for attention and directed action. Thus, an understanding of the production of goal-directed actions must incorporate the higher-level processes involved in the selection of a target stimulus from distractors. To examine the neural substrates of target selection fo...
Presenting a behaviorally irrelevant cue shortly before a target at the same location decreases the latencies of saccades to the target, a phenomenon known as exogenous attention facilitation. It remains unclear whether exogenous attention interacts with early, sensory stages or later, motor planning stages of saccade production. To distinguish bet...
Most visual scenes are complex and crowded, with several different objects competing for attention and action. Thus a complete understanding of the production of goal-directed actions must incorporate the higher-level process of target selection. To examine the neural substrates of target selection for visually guided reaching, we recorded the acti...
We examined the coordination of saccades and reaches in a visual search task in which monkeys were rewarded for reaching to an odd-colored target among distractors. Eye movements were unconstrained, and monkeys typically made one or more saccades before initiating a reach. Target selection for reaching and saccades was highly correlated with the ha...
A salient peripheral cue can capture attention, influencing subsequent responses to a target. Attentional cueing effects have been studied for head-restrained saccades; however, under natural conditions, the head contributes to gaze shifts. We asked whether attention influences head movements in combined eye-head gaze shifts and, if so, whether thi...
Recent evidence indicates that inactivation of the primate superior colliculus (SC) results in an increase in saccade target-selection errors. The pattern of errors suggests that a winner-take-all competition selects the saccade goal and that SC inactivation perturbs this process by biasing the competition against stimuli in the inactivated field....
We examined target selection for visually guided reaching in monkeys using a visual search task in which an odd-colored target was presented with distractors. The colors of the target and distractors were randomly switched in each trial between red and green, and the number of distractors was varied. Previous studies of saccades and attention have...
Saccades in the presence of distractors show significant trajectory curvature. Based on previous work in the superior colliculus (SC), we speculated that curvature arises when a movement is initiated before competition between the target and distractor goals has been fully resolved. To test this hypothesis, we recorded frontal eye field (FEF) activ...
The discharge of neurons in the deeper layers of the superior colliculus (SC) was studied while monkeys performed two visual discrimination tasks that required different amounts of cognitive processing. In a search paradigm the animal's task was to saccade to the location of an odd-colored stimulus located in an array of distractors of uniform colo...
A predator leaps out from behind a rock—that's sure to catch your attention. The idea that certain types of stimuli have a hardwired "hotline" to attention has fascinated psychologists, philosophers, and neuroscientists for more than a century. In 1890, William James enumerated "strange things, moving things, wild animals, bright things, pretty thi...
Saccades are rapid eye movements that orient gaze toward areas of interest in the visual scene. Neural activity correlated with saccade target selection has been identified in several brain regions, including the superior colliculus (SC), but it is not known whether the SC is directly involved in target selection, or whether the SC merely receives...
Important insights into the neural organization of the saccadic system have been gained when the usually stereotyped movement trajectories of saccades have been altered by experimental manipulation. In the present study we produced trajectory variability in monkeys by using a visual search task in which both the location and color of an odd-colored...
When saccadic eye movements are made in a search task that requires selecting a target from distractors, the movements show greater curvature in their trajectories than similar saccades made to single stimuli. To test the hypothesis that this increase in curvature arises from competitive interactions between saccade goals occurring near the time of...
Because real-world scenes typically contain many different potential objects of interest, selecting one goal from many is clearly a fundamental problem faced by the saccadic system. We recorded from visual, movement, and visuo-movement (VM) neurons in the superior colliculus (SC) of monkeys performing a reaction-time visual-search task requiring th...
Because real-world scenes typically contain many different potential objects of interest, selecting one goal from many is clearly a fundamental problem faced by the saccadic system. We recorded from visual, movement, and visuo-movement (VM) neurons in the superior colliculus (SC) of monkeys performing a reaction-time visual-search task requiring th...
Neural studies of oculomotor function in the past have been conducted with the use of very simple visual stimuli. More recently there has been a new emphasis on using more natural stimuli to extend our knowledge of oculomotor organization. Visual search paradigms are an example of the use of these more natural visual surrounds. In search a subject...
Saccades are typically separated by inter-saccadic fixation intervals (ISFIs) of > or =125 ms. During this time, the saccadic system selects a goal and completes the preparatory processes required prior to executing the subsequent movement. However, in tasks in which competing stimuli are presented, two sequentially executed movements to different...
In human subjects, two mechanisms for improving the efficiency of saccades in visual search have recently been described: color priming and concurrent processing of two saccades. Since the monkey provides an important model for understanding the neural underpinnings of target selection in visual search, we sought to explore the degree to which the...
Direct projections from the superior colliculus (SC) to the paramedian pontine reticular formation (PPRF) have been demonstrated anatomically. The PPRF contains cells called excitatory burst neurons (EBNs) that execute the final premotoneuronal processing for saccadic eye movements, as well as other burst cells called long-lead burst neurons (LLBNs...
We provide evidence that the saccadic system can simultaneously program two saccades to different goals. We presented subjects with simple visual search displays in which they were required to make a saccade to an odd-colored target embedded in an array of distractors. When there was strong competition between target and distractor stimuli (due to...
We summarize several experiments indicating that the saccadic system is capable of simultaneously programming two movements toward different goals. This concurrent processing of saccades can lead to the execution of two saccades separated by an extremely short intersaccadic interval. This supports the idea of target competition proposed in Findlay...
We performed two sets of experiments in which observers were instructed to make saccades to an odd colored target embedded in an array of distractors. First, we found that when the colors of the target and distractors switched unpredictably from trial to trial (the mixed condition), saccadic latencies decreased with increasing numbers of distractor...
Smooth pursuit is typically regarded as foveal tracking of simple targets and is therefore usually examined with stimuli such as a small moving dot. In real world situations, however, it is rare to encounter such perceptually minimal stimuli. Can smooth pursuit follow a complex object, such as a movement flow that contains ambiguous local but unamb...
This study examined how variations in the visual scene affect the generation of bimodal saccadic latency distributions, the first mode of which is called the population of “express saccades”. The surface media used to make stimuli visible and the composition of the background were varied to determine the conditions under which express saccades can...
This study had three general points. First, it examined possible visual consequences of frontal lesions. A patient with focal
damage to the subcortical regions of the left frontal lobe, and a small amount of damage near Broca's area, was predicted
to have impaired brain function in posterior regions that are anatomically connected to the damaged si...
One of the most intriguing and controversial observations in oculomotor research in recent years is the phenomenon of express saccades in monkeys and man. These are saccades with such short reaction times (100 msec in man, 70 msec in monkeys) that some experts on eye movements still regard them as artifacts or as anticipatory reactions that do not...
