Geometric-Optical Illusions from Early Visual Cortex: Computational Principles and Top-Down Feedback

01/09/2021 to 31/08/2023

The classical geometric-optical illusions (GIs), i.e. misperceptions of geometric properties when visual contours interact appropriately have defied research efforts to understand them for hundreds of years. Neurophysiological mechanisms in early visual cortex (EVC) have long been implicated for visual perceptual grouping, but their role in the GIs remains largely unexplored. Unsolved questions include: how is visual input distorted in EVC to cause the illusory perceptions? Are top-down feedbacks from higher cortical areas to EVC necessary for the perceptions of GIs? This interdisciplinary project aims to probe these questions with mathematical modeling and psychophysical experiments. First, we build a biologically plausible, nonlinear dynamic model of EVC, capturing the orientation tuning properties and different receptive field sizes of its neurons and the neural connections between these neurons in a recurrent neural circuit, with or without the presence of top-down feedback from higher visual areas. The model will help us to explore how interactions between detectors of visual contour segments could provide a pre-attentive distortion of visual input, and how top-down feedback modulates such interactions, leading to the GIs. Second, we use visual psychophysical experiments to probe and test the GIs, using visual inputs inspired by, and hopefully new GIs predicted by, the model and computational considerations. In both the modeling and experimental components, the central questions include the critical role of the geometric and scale relationships between visual input elements, and the central-peripheral dichotomy, namely the contrast between the central and peripheral visual fields in the availability of top-down feedbacks and in visual acuity. This project will be conducted in Prof. Li Zhaoping’s lab in the Department of Computer Science in the University of Tübingen, taking advantage of the unique combination of theoretical neuroscience and experimental psychology expertise in her lab and the superb infrastructure support.