Spectrally opponent inputs to the human luminance pathway: slow +L and -M cone inputs revealed by low to moderate long-wavelength adaptation.
The luminance pathway has slow (s), spectrally opponent cone inputs in addition to the expected fast (f), non-opponent inputs. The nature of these inputs to luminance flicker perception was further explored psychophysically by measuring middle- (M-) and long-wavelength-sensitive (L-) cone modulation sensitivities, M- and L-cone phase delays, and flicker spectral sensitivities under three conditions of low to moderate long-wavelength adaptation. Under these conditions we find that the luminance channel has fast M- and L-cone input signals (+fM and +fL), and slow, spectrally opponent cone input signals (+sL and -sM). The slow signals found under these conditions are therefore of the opposite polarity to those (+sM and -sL) found under more intense long-wavelength adaptation. At these less intense levels, fast and slow M-cone signals of opposite polarity (-sM and +fM) cancel at low frequencies, but then constructively interfere at intermediate frequencies (ca 12.5-22.5 Hz, depending on adapting level) because of the delay between them. In contrast, fast and slow L-cone signals of the same polarity (+sL and +fL) sum at low frequencies, but then destructively interfere at intermediate frequencies. Importantly, the spectrally opponent signals (+sL and -sM) contribute to flicker nulls without producing visible colour variation. Although its output generates an achromatic percept, the luminance channel has slow spectrally opponent as well as fast non-opponent inputs.
Stockman
Andrew
A
Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK. a.stockman@ucl.ac.uk
Plummer
Daniel J
DJ
D000222:Adaptation, Physiological / Q000502:physiology; D003116:Color; D003118:Color Perception / Q000502:physiology*; D003119:Color Perception Tests / Q000379:methods; D006801:Humans; D008297:Male; D009473:Neuronal Plasticity / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*