Evidence for the stochastic independence of the blue-yellow, red-green and luminance detection mechanisms revealed by subthreshold summation.
We investigated the manner in which the outputs of the three postreceptoral mechanisms (red-green, blue-yellow and luminance) combine to determine contrast threshold. We used a subthreshold summation paradigm to test whether the combination of the postreceptoral mechanism outputs could be described by a probability summation model which assumes stochastic independence of the mechanisms, and determined the best fitting summation exponent. Stimuli were Gaussian enveloped 1 c/d sinusoidal gratings represented in a 3D cardinal space transformed from cone contrast axes, and normalized to detection threshold. The use of this space avoids the presence of elongated threshold contours, allowing a reliable model fit to include the less sensitive blue-yellow and luminance mechanisms. Our results were well fitted by the probability summation model and hence support the underlying stochastic independence of the three postreceptoral mechanisms.
Mullen
K T
KT
Department of Ophthalmology, McGill Vision Research, McGill University, Montreal, Canada. kmullen@violet.vision.mcgill.ca
Sankeralli
M J
MJ
D016009:Chi-Square Distribution; D003118:Color Perception / Q000502:physiology*; D003119:Color Perception Tests; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008960:Models, Psychological