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Anna Ma-Wyatt, Adam Kane, Alex Wade; Delays in using chromatic and luminance information for a simple reaction time task. Journal of Vision 2012;12(9):823. doi: 10.1167/12.9.823.
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The human visual system has three geniculate pathways that transmit information from the retina to cortex. The chromatic (L-M) and S-(L+M) pathways are thought to have slower conduction velocities than the achromatic (L+M+S) pathway and these delays may, in turn, result in slower reaction times (RTs) to chromatic stimuli. However, adjusting for individual differences in chromatic sensitivity and equating stimulus contrast across the three pathways are essential if we are to compare chromatic and achromatic RTs. Here, we measured chromatic and achromatic RTs over a range of contrasts and expressed them as functions of both detection thresholds and estimated neural activity. Chromatic stimuli were adjusted to be equiluminant to a grey background for each participant. Detection thresholds and JNDs were measured for chromatic and achromatic Gaussian blobs presented at 2° eccentricity. To generate accurate S-cone isolating stimuli we also measured participants’ tritan lines using a sensitive ‘transient tritanopia’ procedure. We then measured the time it took subjects to raise a finger in response to the appearance of a calibrated Gaussian blob of a given chromaticity and contrast. RTs decreased monotonically as a function of contrast and RTs for achromatic stimuli were approximately 45ms faster than for chromatic stimuli. We model these data within the framework of a model that incorporates a first stage integrative yielding a strong stimulus contrast dependency and a second stage that converts decisions into motor activity.
Meeting abstract presented at VSS 2012
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