Jessica Beamish – Abstract

Transient, broad field, visual input strongly modulates reactive saccade latency

Beamish J[1], Loeb G[2], Corneil B[3], Marinovic W[4], Wallis G[1], Carroll T[1]

  1. Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Australia.
  2. Department of Biomedical Engineering, University of Southern California, Los Angeles, USA.
  3. Brain and Mind Institute, University of Western Ontario, London, Canada.
  4. School of Psychology and Speech Pathology, Curtin University, Perth, Australia.

In humans, the superior colliculus is a key midbrain node for the control of saccadic gaze shifts (and possibly some limb movements [1]). Its role is illustrated by “express saccades”, which occur when the first arrival of sensory information from the retina and/or primary visual cortex triggers very short latency gaze shifts (<110ms). Here we sought a method to experimentally manipulate the state of the superior colliculus, and thereby modulate the latency of saccadic initiation to visual targets. We presented black and white checkerboard stimuli over a large proportion of the visual field (~57 x 32 degrees of visual angle) for 8ms, at seven different timings with respect to the appearance of left or right saccade targets (-83ms to 58ms). We characterised the effect of checkerboard presentation timing on saccade properties (reaction time, directional error and amplitude) in ten people, to test the hypothesis that the stimulus would influence the latency but not the metrics of saccades. Checkerboard stimuli presented 83ms prior to the target reduced reaction time in all participants (from 113.5 [26.0] to 98.0 [7.8] ms; median [IQR]), whereas reaction times dramatically increased for checkerboard stimuli presented immediately before (162.3 [11.8] ms) or after the target (138.8 [27.8] ms). The checkerboard stimuli did not compromise movement accuracy at any timing; there were no effects on directional error or amplitude. The data suggest that broad field visual input can dramatically modulate saccade onset latency. The general approach might be beneficial in treatment for people with disorders of movement initiation.

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