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Françoise Vitu, Soazig Casteau, Delphine Massendari, Lotje van der Linden; How the distorted representation of visual space in our brain constrains the way we move our eyes.. Journal of Vision 2014;14(10):751. doi: 10.1167/14.10.751.
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The representation of visual space is distorted in several areas of the brain, including the Superior Colliculus (SC) where population averaging presumably determines the amplitude of saccadic eye movements. We previously showed, based on human behavioral data that this is responsible for the rather systematic tendency to undershoot the center of eccentric, simple-shape stimuli (Vitu & Casteau, VSS 2013). Here, we reveal that population averaging in the distorted map of the SC is a general principle that accounts for the metrics of saccades towards stimuli of varying sizes and shapes, irrespective of the task and the cognitive content of the stimuli, and wherever stimuli appear in the visual field. Our demonstration relies on a very simple approach that consists of (1) recording the eye movements of human participants while they execute a range of tasks (from aiming at the center of a single peripheral visual target to reading series of words), and (2) plotting the distributions of the eyes' initial landing sites in both visual and collicular spaces, using for the latter, Ottes et al.'s (1986) logarithmic mapping function of the SC in monkeys. We observe that as stimuli are presented more peripherally, landing sites, when expressed in degrees of visual angle, become more variable and are more greatly biased towards the fovea. However, landing sites, when expressed in millimeters of collicular space are normally distributed around the center of the stimulus image, and with comparable variability. Thus, where the eyes move is strongly constrained by the tendency for neural activity in the distorted map of the SC, to build up at the center of the stimulus pattern. The neural bases of saccade programming and implications for models of eye guidance in complex cognitive tasks will be discussed.
Meeting abstract presented at VSS 2014
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