Colour adaptation modifies the long‐wave versus middle‐wave cone weights and temporal phases in human luminance (but not red‐green) mechanism.

Abstract

1. The human luminance (LUM) mechanism detects rapid flicker and motion, responding to a linear sum of contrast signals, L' and M', from the long-wave (L) and middle-wave (M) cones. The red-green mechanism detects hue variations, responding to a linear difference of L' and M' contrast signals. 2. The two detection mechanisms were isolated to assess how chromatic adaptation affects summation of L' and M' signals in each mechanism. On coloured background (from blue to red), we measured, as a function of temporal frequency, both the relative temporal phase of the L' and M' signals producing optimal summation and the relative L' and M' contrast weights of the signals (at the optimal phase for summation). 3. Within the red-green mechanism at 6 Hz, the phase shift between the L' and M' signals was negligible on each coloured field, and the L' and M' contrast weights were equal and of opposite sign. 4. Relative phase shifts between the L' and M' signals in the LUM mechanism were markedly affected by adapting field colour. For stimuli of 1 cycle deg' and 9 Hz, the temporal phase shift was zero on a green-yellow field (-570 nm). On an orange field, the L' signal lagged M' by as much as 70 deg phase while on a green field M' lagged L' by as much as 70 deg. The asymmetric phase shift about yellow adaptation reveals a spectrally opponent process which controls the phase shift. The phase shift occurs at an early site, for colour adaptation of the other eye had no effect, and the phase shift measured monocularly was identical for flicker and motion, thus occurring before the motion signal is extracted (this requires an extra delay). 5. The L' versus M' phase shift in the LUM mechanism was generally greatest at intermediate temporal frequencies (4)(5)(6)(7)(8)(9)(10)(11)(12) and was small at high frequencies (20-25 Hz). The phase shift was greatest at low spatial frequencies and strongly reduced at high spatial frequencies (5 cycle deg-'),indicating that the receptive field surround of neurones is important for the phase shift. 6. These temporal phase shifts were confirmed by measuring motion contrast thresholds for drifting L cone and M cone gratings summed in different spatial phases. Owing to the large phase shifts on green or orange fields, the L and M components were detected about equally well by the LUM mechanism (at 1 cycle deg-' and 9 Hz) when summed spatially in phase or in antiphase. Antiphase summation is typically thought to produce an equiluminant red-green grating. 7. At low spatial frequency, the relative L' and M' contrast weights in the LUM mechanism (assessed at the optimal phase for summation) changed strongly with field colour and temporal frequency. (-20ims) relative to the centre.

A linear chromatic mechanism drives the pupillary response

“…Pokorny et al (1993) showed that, for a 570 nm yellow background ¢eld, the red:green ratio in £icker detection was approximately constant with respect to changes in the mean luminance. Stromeyer et al (1997) also showed that the ratio of the long wavelength cone and middle wavelength cone inputs to the luminance mechanism were constant with respect to the change in the spatial and temporal frequencies.…”

“…It would appear that pupillary responses can be separately driven by both luminance and chromatic stimuli and that, in agreement with psychophysical studies, at lower spatio-temporal frequencies, the sensitivity of pupillary responses to the chromatic mechanism is higher than that for the luminance mechanism. For instance, Stromeyer et al (1995) showed the sensitivity of the chromatic mechanism to be seven times higher than that for the luminance mechanism for detecting a grating at low temporal (1Hz) and low spatial (1 cycle degree 71 ) frequencies.…”

“…Chaparro et al 1995). If the jL + Mj luminance mechanism drives pupillary responses, the contour should form a straight line with a negative slope (Stromeyer et al 1997;Tsujimura et al 1999Tsujimura et al , 2000. However, if a nonlinear mechanism drives pupillary responses, the contour will also be nonlinear.…”

Temporal sensitivity of macaque ganglion cells to lights of different chromaticity

“…[1][2][3][4] This article addresses the physiological underpinnings of three phenomena, which involve chromatic adaptation and temporal stimulus modulation.…”

Bar-like S-cone stimuli reveal the importance of an intermediate temporal filter

“…Accordingly, two temporal filters for red-green grating stimuli have been explicitly reported using Gabor patches [9,10]; a low-pass filter (sustained ), and a second band-pass filter (transient-2 ). There are strong residual achromatic contributions due to the L-and M-cone phase shifts for red-green stimuli [11,12], and this makes it more difficult to separate either of them from the luminance mechanism. Hence, the intermediate band-pass temporal filter (transient-1 ) has never been proposed as underlying detection of diffuse chromatic spots.…”