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Mark P Burton, Paul V McGraw, Chris Scholes, Neil W Roach; Improving the efficiency of oculometric measures of contrast sensitivity. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5901. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Variations in microsaccade rate, time-locked to the onset of visual stimuli, can be used to objectively measure observers’ contrast sensitivity during passive viewing. However, current methods for doing this use sparse stimulus sequences and require substantial testing time to achieve an acceptable level of precision. Here we investigate whether rapid stimulus sequences varying in number, frequency and contrast can improve testing efficiency.
Observers were asked to maintain fixation, while trains of brief (~11.8ms) stimuli were presented. Each stimulus in the sequences was a randomly oriented 0.33c/deg Gabor patch. Eye position was recorded binocularly at 500Hz using an Eyelink 1000 infrared eye tracker and microsaccades were identified using a velocity-based algorithm. Across three experiments we either presented: two fixed contrast stimuli at a range of inter-stimulus intervals (ISI=100, 200, 400 or 800ms); trains of 1, 2, 4, 8 or 16 stimuli with fixed contrast and ISI; and trains of 8 stimuli with fixed ISI that either increased or decreased in log-contrast over time.
When pairs of stimuli were presented at ISIs above 200ms, each produced a distinctive biphasic modulation in microsaccade rate that was comparable to that obtained with a single isolated stimulus. With shorter ISIs however, the inhibitory phase of this rate ‘signature’ was prolonged throughout the stimulus presentation period. Variation of contrast across longer trains of stimuli produced distinct effects – microsaccade inhibition was maintained in descending sequences until the contrast fell below detection threshold, whereas a more steady, incremental inhibition profile was observed for ascending sequences.
Rapid trains of visual stimuli produce systematic modulations in microsaccade rate. Such sequences have the potential to increase the efficiency of methods that exploit eye movements to make objective measurements of contrast sensitivity. Sequences of contrast-varying stimuli may even allow the estimation of detection threshold directly from features of the time-varying microsaccade rate signature.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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