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John Erik Vanston, Michael Crognale; Chromatic visual evoked potentials using customized color space. Journal of Vision 2015;15(12):255. doi: 10.1167/15.12.255.
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© 2017 Association for Research in Vision and Ophthalmology.
Chromatic visual evoked potential (cVEPs) and psychophysics are often used to characterize isolated color or cone-opponent systems for various purposes. Retinal inhomogeneities across the visual field can introduce color shifts and luminance artifacts to uniform, large-field stimuli. It may be useful, therefore, to design customized stimuli that correct for the retinal inhomogeneities of observers. We created large-field stimuli equated across the visual field for luminance and hue shifts using psychophysical methods. We also evaluated the effects of applying corrected stimuli on the waveform of the cVEP. Five subjects viewed full-field onset stimuli. Stimuli comprised a field of gabor patches composed of colors modulated along nominal LM- and S-axes; in some conditions, colors of the gabor patches were customized using psychophysical settings made by the observer, such that axis contrasts were perceptually equated by suprathreshold contrast matching, and individuals’ tritan axes were determined using the minimally distinct border technique. Stimuli were equated for luminance by flicker photometry. Isoluminance and tritan directions were determined across five levels of retinal eccentricity, including foveal and extrafoveal regions. cVEPs were recorded using both nominal and customized stimuli. Equating stimuli for perceptual salience and adjusting S-axis stimuli to modulate along an individual’s tritan axis did not have a strong effect on the waveform of the chromatic VEP. Compared to responses using normal tritan stimuli, responses for “individual” tritan stimuli differed little in latency and only moderately in amplitude. Nonetheless, waveforms for both types of S-cone stimuli were different from those of LM-cone stimuli in latency and amplitude. Many psychophysical techniques (e.g. threshold measurement) are sensitive to small changes in luminance and chromaticity and would benefit from utilizing an observer-specific color space and stimuli adjusted for retinal inhomogeneity. However, the cVEP appears to be robust to retinal inhomogeneity, likely due in part to cortical magnification.
Meeting abstract presented at VSS 2015
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