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M. Rodriguez-Carmona, J.A. Harlow, J.L. Barbur; Pupil Responses to Chromatic Afterimages . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1917.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Pupil responses to isoluminant chromatic stimuli and the corresponding chromatic afterimages have been reported in previous studies, but the mechanisms involved in both of these effects remain poorly understood. The purpose of this study was to establish how chromatic afterimages are generated and whether the pupil constrictions recorded both at the onset and the offset of an isoluminant coloured stimulus reflect the activity of the same or different mechanisms. Methods: Pupil responses were recorded when the eye was presented with either flashed or sinusoidally modulated chromatic stimuli. Two of the colours employed were photopically and scotopically isoluminant. Pupil responses to colours that were only photopically isoluminant were also measured. In addition, pupil responses to achromatic luminance increments and decrements were studied. Other parameters investigated include chromatic signal strength and the effect of adding dynamic luminance contrast (LC) noise. The amplitude and the spatiotemporal properties of this background noise were varied systematically and the corresponding pupil responses examined. Results: Pupil responses can be elicited both at the onset and the offset of chromatic stimuli. "Red" chromatic afterimages generated by a "green" colour, photopically and scotopically isoluminant, was found to be particularly effective in driving the pupil response. The results show that pupil responses to sinusoidally modulated chromatic afterimages lag behind the primary stimulus by exactly half a cycle. In the case of flashed stimuli, the pupil responses generated, both at stimulus onset and offset remain unaffected by the presence of dynamic LC noise. This was not however the case when the stimulus was defined by luminance contrast or the coloured stimulus was only photopically isoluminant. Conclusions: The results show that significant pupil responses to both stimulus onset and offset are observed in response to photopically and scotopically isoluminant colours. When achromatic stimuli are defined by luminance signals, the presence of dynamic LC noise causes a significant reduction in pupil response amplitude, even when the increment in light flux remains unchanged. In contrast to this observation, for coloured stimuli, buried in dynamic LC noise, there is no significant reduction in pupil response amplitude at both stimulus onset and offset. This observation suggests that colour mechanisms also mediate the generation of chromatic afterimages and that the same chromatic processes may generate the corresponding pupil responses.
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