Visual-motor neural mechanisms underlying peri-saccadic perceptual alterations

Abstract

This thesis explores the visual and motor mechanisms underlying saccadic suppression and perceptual stability, focusing on two interrelated aspects. The first part investigates saccadic suppression, the phenomenon where visual sensitivity is reduced during saccades to prevent motion blur and ensure spatial coherence. Traditionally attributed to motor signals such as corollary discharge, this work demonstrates that visual mechanisms play a more prominent role than previously assumed. The second part revisits motor bursts in the superior colliculus (SC), traditionally regarded as purely motoric, and uncovers their contribution to visual stability through sensory-motor integration. The first study established the visual origins of saccadic suppression using retinal recordings and human psychophysics. By simulating saccades, suppression was induced without motor signals, driven by stimulus characteristics like spatial frequency and texture. Low spatial frequencies and coarse textures elicited stronger suppression, challenging motor-centric models and highlighting stimulus-stimulus interactions. The second study examined the influence of luminance contrast polarity on suppression. Psychophysical experiments revealed stronger suppression for dark stimuli on dark backgrounds, even during simulated saccades, further emphasizing the contextual and visually driven nature of suppression. In the second part, the role of the SC in sensory-motor integration was investigated. The third study demonstrated that SC motor bursts, traditionally viewed as purely motoric, are modulated by the visual properties of saccade targets, such as spatial frequency and contrast. This finding highlights the SC’s dual function in encoding visual features and generating predictive signals for eye movements. The fourth study addressed perisaccadic mislocalization, where visual stimuli are perceived inaccurately during saccades. Human psychophysics revealed that mislocalization depends on visual features and varies across the visual field, with stronger effects in the upper field. Finally, a novel paradigm confirmed these mislocalization patterns in rhesus macaques, showing parallels with human findings. Mislocalization strength varied with saccade direction and visual field location, supporting the SC’s role in visual stability and providing a robust framework for future research. Together, this work reveals that both saccadic suppression and visual stability rely heavily on visual mechanisms and the SC’s sensory-motor integration, offering a refined understanding of how seamless vision is maintained during eye movements.