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Chris Scholes, Neil Roach, Marcus Nyström, Paul McGraw; Contrast sensitivity of microsaccade rate signature. Journal of Vision 2015;15(12):212. doi: https://doi.org/10.1167/15.12.212.
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During periods of steady fixation, individuals make small ballistic eye movements (microsaccades) at a rate of around 1-2 per second. Presentation of a visual stimulus triggers a biphasic modulation in microsaccade rate – an initial inhibition followed by a period of elevated rate and a subsequent return to baseline. The magnitude and latency of this characteristic ‘rate signature’ have previously been shown to change with large manipulations of stimulus contrast (Rolfs et al., 2008). Here, we examine the contrast sensitivity of the rate signature and its relationship to individuals’ psychophysical detection thresholds. Observers were required to fixate on a central dot, while large Gabor patches (SF = 0.33 c/deg; 11.8 deg. full-width/half-height) of varying contrast were presented briefly (12 ms), centered on fixation. On a subset of trials within each run, observers were cued to discriminate the orientation of the Gabor (±45°). Binocular eye position was recorded at 500Hz using an Eyelink-1000 and microsaccades were identified using criteria described by Engbert & Kliegl (2003) and Engbert (2006). Data were obtained for seven observers at 11 contrast levels; each observer completed at least 900 passive trials per contrast. Analysis of passive trials revealed statistically reliable rate signatures across a range of contrasts. For each observer, oculometric functions were constructed from changes in the magnitude and/or latency of the rate signature, or using pattern classification techniques. Resulting estimates of contrast sensitivity approached those obtained psychophysically. These findings indicate that stimulus-induced modulations of microsaccade rate are highly sensitive to absolute contrast. As a consequence, the rate signature could provide a novel means of quantifying visual sensitivity without the need for observers to make a stimulus judgment.
Meeting abstract presented at VSS 2015
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