Achromatic impulses unmask L- and M-cone adaptive mechanisms.
The mechanisms underlying the adaptive response for achromatic impulses seen on achromatic fields were investigated. Foveal thresholds were measured for a static probe-impulse under two conditions of adaptation. Thresholds were obtained under gain-clamped conditions after observers had reached steady-state adaptation and with a probe-flash paradigm. It was found that thresholds isolated on steady-state fields cannot be modelled using a single mechanism. Likewise, the probe-flash condition failed to reflect the response of a single mechanism. Both threshold functions showed distinct breaks occurring at about the same field luminance (approximately 1.0 log cd/m2). Optimum data fits required the incorporation of two mechanisms implying the existence of independent processes mediating detection. Chromatic isolation confirmed that differential adaptation had been unmasked in the long- and medium-wavelength sensitive cone inputs to the achromatic channel.
Zele
A J
AJ
Department of Optometry and Vision Sciences, University of Melbourne, Victoria, Australia.
Vingrys
A J
AJ
D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D003118:Color Perception / Q000502:physiology; D004596:Electroretinography; D006801:Humans; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*