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J. M. Medina; Rectified chromatic detection mechanisms at suprathreshold isoluminance conditions. Journal of Vision 2004;4(11):68. doi: 10.1167/4.11.68.
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In the present work, I studied whether isoluminance mechanisms can be influenced by the polarity of the signal producing separate red, green, yellow and blue responses. I used visual latencies to determine whether this paradigm can be applied to post-receptoral mechanisms at suprathreshold conditions. Simple visual-reaction times were measured at the fovea for circular random step-wise stimuli presented on a colour monitor at a 1.5-deg field size. Stimulus chromaticity was selected according to Boynton's two-stage color-vision model (Boynton, 1986), along an L&M-constant cone axis and an S-constant cone axis. A 15 cd/m2 achromatic reference stimulus was selected to provide red, green, yellow or blue suprathreshold isoluminance changes (six visual stimuli in each case). The heterochromatic flicker photometry method was used to obtain the equiluminance level. Simple visual-reaction times for manual responses were registered on fovea using the standard procedure (Nissen & Pokorny, 1977). Two human observers with normal color vision took part in the experiment. To examine the rate at which responses were produced at each time following stimulus presentation (events per millisecond), the hazard functions were calculated from reaction time raw data using the standard procedure (Luce, 1986). Comparing these functions for each pair of stimuli selected, it is concluded that there are asymmetries at long processing times due to the polarity of the signal. These results suggest the existence of a red-green and a yellow-blue rectified separate process at suprathreshold conditions, corroborating the splitting process found at the threshold (Sankeralli & Mullen, 2001).
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