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Trans-saccadic prediction error re-calibrates perceived size in the peripheral visual field

43.3028, Monday, 18-May, 8:30 am - 12:30 pm, Banyan Breezeway
Session: Eye Movements: Cognition and models

Matteo Valsecchi1, Karl Gegenfurtner1; 1Department of Psychology, Justus-Liebig-University Giessen

Our visual world appears uniform despite the fact that the properties of our visual system change dramatically between foveal and peripheral vision. This might be explained by the fact that our visual system is able to predict the changes in sensory inputs associated with our eye movements and use potential prediction errors in order to maintain perceptual calibration. In a series of experiments we investigated whether the repeated exposure to a trans-saccadic change in the size of the object being foveated can lead to a change in its perceived size when viewed peripherally. In each trial, observers first compared the size of a centrally presented approximately circular stimulus (radius 1.65°) with a similar stimulus presented at the same time 20° in the peripheral visual field. The size of the peripheral stimulus varied between trials following an adaptive staircase. After the size judgment, the observers looked directly to the peripheral stimulus and performed a difficult shape discrimination. After 100 trials in which each observer´s baseline peripheral size PSE was established, a gaze-contingent change in the peripheral stimulus was introduced when the observers saccaded towards it (10% radius increase/decrease in separate groups, N=8+8). Over the following 400 trials the PSE decreased by around 8% in the decrease group, whereas it remained relatively constant in the increase group. Most observers did not notice the trans-saccadic change. In further experiments we found that the change in perceived size persisted when the observers were no longer required to saccade to the peripheral stimulus. If the trans-saccadic manipulation of the stimulus size was only experienced in one visual hemifield during training, its effect generalized to the opposite hemifield with similar gain. The results suggest that our impression of uniformity between central and peripheral vision is due to a constant and relatively quick process of sensori-motor re-calibration.

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