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John Erik Vanston, Alexandra E Boehm, William Scott Tuten, Austin John Roorda; Influence of stimulus size, intensity, & natural eye motion on small-field color perception. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2819.
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© ARVO (1962-2015); The Authors (2016-present)
Stimulating single cones with spots of 543nm light has been shown to elicit various color sensations. These percepts vary mainly along a red-green axis, yet large fields of this wavelength invariably appear green and highly saturated. It remains unknown what conditions, if any, reliably yield veridical color percepts at the photoreceptor scale. Notably, naturalistic viewing includes eye motion, which causes many cones to sample the stimulus across time. The current study varied stimulus size and intensity under two eye motion conditions in order to better understand how chromatic percepts are constructed from cone signals.
Stimuli comprised 543nm spots of light presented at ~1 deg temporal eccentricity using an adaptive optics scanning laser ophthalmoscope. This system corrects for the optical aberrations of the eye and provides high-precision eye tracking and stimulus delivery. On each trial small spots of light were delivered to the retina over 500 ms. Stimuli were presented at two sizes (~2 and 4 arcmin, respectively), two intensities (1x and 6x detection threshold), and two eye motion conditions. In the first condition, stimuli were presented to a fixed position on the retina; in the second condition, stimuli were initially presented to a predefined retinal location, but subsequently allowed to drift across the moving cone mosaic. On each trial subjects (n = 3) reported the perceived saturation (rating scale of 1-5) and hue (red, white, or green) of the stimulus.
The mean likelihood that subjects reported green increased for larger and higher intensity stimuli, with size increasing this likelihood from 74% to 85% and intensity increasing it from 72% to 86%. Similar results were found for saturation, with larger size resulting in a 7% increase in mean saturation rating and higher intensity resulting in a 10% increase. Varying eye motion resulted in a difference of only 1% in both measures. The amount of eye motion was found to be uncorrelated to the saturation rating on a trial-to-trial basis.
When small groups of cones were stimulated with 543 nm light, increases in stimulus size and intensity resulted in percepts that appeared more saturated and more consistently greenish, rather than reddish or whitish, in hue. Whether these spots of light were stabilized on the retina or allowed to drift freely across it made little difference in hue or saturation reports.
This is a 2021 ARVO Annual Meeting abstract.
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