Vision and eye movements

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Résumé :

The existence of a central fovea, the small retinal region with high analytical performance, is arguably the most prominent design feature of the primate visual system. This centralization comes along with the corresponding capability to move the eyes to reposition the fovea continuously. Past research on perception was mainly concerned with foveal vision while the eyes were stationary. In my talk I will compare human visual perception with and without eye movements to emphasize different aspects and functions of eye movements. I will argue that our visual system has evolved to optimize the interaction between perception and the active sampling of information.

Recently we have shown that lightness judgments are significantly determined by where on an object we fixate. When we look at regions that are darker due to illumination effects, the whole uniformly colored object appears darker, and vice versa for brighter regions. Under free viewing conditions, fixations are not chosen randomly. Observers prefer those points that are maximally informative about the object’s lightness.

For pursuit eye movements, we have shown that our sensitivity to visual stimuli is dynamically adjusted when pursuit is initiated. As a consequence of these adjustments, colored stimuli are actually seen better during pursuit than during fixation and small changes in the speed and direction of the object are more easily detected, enabling a better tracking of moving objects. Pursuit itself increases our ability to predict the future path of motion, lending empirical support to the widespread belief that in sports it’s a good idea to keep your eyes on the ball. These results demonstrate that the movements of our eyes and visual information uptake are intricately intertwined. The two processes interact to enable an optimal vision of the world, one that we cannot fully grasp while fixating a small spot on a display.