Colour adaptation modifies the temporal properties of the long- and middle-wave cone signals in the human luminance mechanism.

The human luminance mechanism (LUM) detects rapid flicker and motion, summating the neurally integrated L' and M' 'contrast' signals from the long- and middle-wave cones, respectively. We previously observed large temporal phase shifts between the L' and M' signals in LUM, which were maximal and of reversed sign on green versus orange background fields and which were accompanied by large variations in the relative L' and M' contrast weights. The effects were modelled with phasic magnocellar retinal ganglion cells. The changing L' versus M' contrast weights in the model predict that the temporal dynamics of the L' and M' luminance signals will differ on green and orange fields. This is assessed with several protocols. Motion thresholds for 1 cycle deg(-1) drifting gratings or static pulsed gratings on the orange field show that the M' signal is more temporally bandpass than the L' signal; this reverses on the green field. Strong motion due to the different dynamics of the L' and M' signals is even seen with a pair of L' and M' gratings pulsed simultaneously. Impulse response functions were measured with gratings pulsed spatially in phase or antiphase. The impulse response was clearly biphasic for the M' signal on the orange field and L' signal on the green field, while the other signals were more sustained. The impulse responses predicted the motion seen with gratings pulsed in spatial quadrature.