Zhuanghua Shi's research while affiliated with Ludwig-Maximilians-University of Munich and other places

How we perceive a visual stimulus can be influenced by its surrounding context. For example, the presence of a reference skews the perception of a similar feature in a stimulus, a phenomenon called reference repulsion. Ongoing research so far remains inconclusive regarding the stage of visual information processing where such repulsion occurs. We examined the influence of a reference on late visual processing. We measured the repulsion effect caused by an orientation reference presented after an orientation ensemble stimulus. The participants’ reported orientations were significantly biased away from the post-stimulus reference, displaying typical characteristics of reference repulsion. Moreover, explicit discrimination choices between the reference and the stimulus influenced the magnitudes of repulsion effects, which can be explained by an encoding-decoding model that differentiates the re-weighting of sensory representations in implicit and explicit processes. These results support the notion that reference repulsion may arise at a late decision-related stage of visual processing, where different sensory decoding strategies are employed depending on the specific task.

Incorporating statistical characteristics of stimuli in perceptual processing can be highly beneficial for reliable estimation to overcome noisy sensory measurements but may generate perceptual bias. According to Bayesian inference, perceptual biases arise from integrating non-uniform internal priors with noisy sensory inputs. We used a Bayesian observer model to derive biases and priors in hue perception based on discrimination data for hue ensembles with varying levels of chromatic noise. For isoluminant stimuli with hue defined by azimuth angle in cone-opponent color space, discrimination thresholds showed a bimodal pattern, with lowest thresholds near a non-cardinal blue-yellow axis that aligns closely with the variation of natural daylights. Perceptual biases showed zero crossings around this axis, indicating repulsion away from yellow and attraction towards blue. The results could be explained by the Bayesian observer model through a non-uniform prior with a preference for blue. Our results indicate that observers exploit knowledge of colors in natural environments in visual processing for hue perception. Author Summary Human visual perception is susceptible to systematic biases consistent with an optimal inference process that combines sensory evidence with prior knowledge. It has been hypothesized that, to make accurate inferences, the brain adapts to the sensory world and develops a prior that reflects environmental statistics. Our research on hue perception supports this idea, which demonstrates that color discrimination exhibits a consistent preference towards blue and away from yellow, which can be attributed to the influence of natural daylights that are dominated by blue and yellow. Our results are predicted by a Bayesian model incorporating prior knowledge about natural daylights, which provides insight into how humans adapt to these lighting conditions and use natural color statistics in hue perception.