Towards a unified theory of microsaccadic and saccadic function: determining the significance of microsaccades for perception, cognition, and oculomotor control

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Saccadic eye movements -- the eye movements that shift our gaze during exploration of a visual scene --play multiple roles that are critical to visual perception. They bring high-interest targets to the center of our vision, they search and integrate general information about the environment to stitch together each visual scene, they correct gaze errors, and they are a primary mechanism to direct our attention. When we fixate our gaze between saccades, our eyes nevertheless move constantly, producing so called fixational eye movements. There is disagreement about the impact of fixational eye movements on visibility during fixation, their accuracy in correcting fixation errors, and their relationship with attention and other cognitive processes. Most of these controversies focus on the main roles historically attributed to microsaccades -the largest and fastest fixational eye movement-, such as the prevention and restoration of vision loss during fixation and the correction of fixation errors. The investigators will conduct eye movement experiments and analyses in human observers so as to determine the effects of microsaccades on the visibility of a large range of stimuli and on the correction of oculomotor error during fixation.We fixate our gaze about 80% of the time during visual exploration, and so understanding the perceptual effects of fixational eye movements is critical to understanding vision. The project aims to widen the scope of microsaccades from having a single or primary function to playing multiple non-exclusive roles in vision, in the same fashion as large saccades do. As such, the investigators will set out to determine whether microsaccades restore the visibility of all faded stimuli -or only that of a narrow range of stimuli- and to elucidate the role of microsaccades in the correction of fixation error. Understanding how microsaccades affect visibility as a function of stimulus characteristics will moreover improve the interpretation of visual studies, most of which are conducted under fixation conditions. Finally, determining that microsaccades re-target fixation after gaze position errors may help engineers to account for these effects in the design of displays and procedures to improve accuracy when operating equipment.