Impact of eye movements on the visual crowding effect



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To study the role of eye movements of different magnitudes on the perception of a crowded stimulus. Given that eye movements are ubiquitous, and essential in helping us navigate our surroundings, understanding their implications in visual perception is a crucial step in understanding visual processing.Five experiments are described: (1) We characterized the oculomotor behavior of normally sighted individuals who were trained to use different artificial preferred retina loci (PRL) positioned in distinct locations of the visual field when performing a reading-like visual task. (2) We monitored microsaccadic behavior (a proposed attentional correlate) to understand how naturally occurring shifts in attention following the presentation of a crowded stimulus affect visual performance. (3) We investigated the role of microsaccadic preparation when crowded stimuli were presented at a future microsaccade goal 20 arc minutes from the center of gaze. (4) Using the same paradigm, we investigated the effect of microsaccade preparation on the shape of the crowding zone. (5) We further dissociated the microsaccadic goal and the stimulus location to understand the effect of microsaccadic preparation on performance at other locations within the foveola.(1) We observed that a right artificial PRL caused the spontaneous development of excessively large saccades and more direction switches. (2) The spatial extent of visual crowding was found to decrease by 26% on trials which contained incongruent microsaccades (proposed to indicate attentional capture). (3) The influence of microsaccade preparation on performance was variable between subjects, with the temporal pattern across subjects indicating a general enhancement across most target-flanker spacings tested. (4) When crowded stimuli were presented within 50 ms from microsaccadic onset an exclusive benefit in performance was observed when flankers were oriented along the tangential axis. (5) When the saccade goal differed from the stimulus location, the benefit in performance immediately before microsaccadic onset was no longer present.Different PRL positions lead to different oculomotor patterns, which we suggest may help explain biases in PRL selection amongst individuals with central visual loss. Fixational eye movements have diverse impacts on crowded stimuli at different eccentricities from the center of gaze.



Eye movements, Visual crowding, Simulated central visual loss, Preferred retinal locus


Portions of this document appear in: Prahalad, K. S., & Coates, D. R. (2020). Asymmetries of reading eye movements in simulated central vision loss. Vision research, 171, 1-10; and in: Prahalad, K. S., & Coates, D. R. (2022). Microsaccadic correlates of covert attention and crowding. Journal of Vision, 22(10), 15-15.