Absence of linear subthreshold summation between red-green and luminance mechanisms over a wide range of spatio-temporal conditions.
We have tested the independence of red-green chromatic and luminance mechanisms at detection threshold using a method of subthreshold summation. Stimuli were isoluminant red-green gratings and yellow-black luminance gratings that uniquely activate the red-green color and luminance mechanisms, respectively. Stimuli were Gaussian enveloped 0.25, 1 or 4 cpd sinewave gratings, counter-phase flickered at 0, 5 or 9 Hz. The threshold detection of red-green color contrast was measured in the presence of a subthreshold amount of luminance contrast, and vice versa. The results allow a model of linear summation between the color and luminance mechanisms to be rejected, but are well fitted by a model, assuming that these mechanisms are independent but combine to determine detection by probability summation, with a high summation index (median value = 4). We conclude that there are independent red-green chromatic mechanism and luminance detection mechanisms over this range of spatio-temporal conditions.
Mullen
K T
KT
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Canada. kmullen@violet.vision.mcgill.ca
Cropper
S J
SJ
Losada
M A
MA
D003118:Color Perception / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008959:Models, Neurological; D010364:Pattern Recognition, Visual / Q000502:physiology; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology