Temporal dynamics of chromatic tuning in macaque primary visual cortex

Abstract

The ability to distinguish colour from intensity variations is a difficult computational problem for the visual system because each of the three cone photoreceptor types absorb all wavelengths of light, although their peak sensitivities are at relatively short (S cones), medium (M cones), or long (L cones) wavelengths. The first stage in colour processing is the comparison of the outputs of different cone types by spectrally opponent neurons in the retina and upstream in the lateral geniculate nucleus. Some neurons receive opponent inputs from L and M cones, whereas others receive input from S cones opposed by combined signals from L and M cones. Here we report how the outputs of the L/M- and S-opponent geniculate cell types are combined in time at the next stage of colour processing, in the macaque primary visual cortex (V1). Some V1 neurons respond to a single chromatic region, with either a short (68-95 ms) or a longer (96-135 ms) latency, whereas others respond to two chromatic regions with a difference in latency of 20-30 ms. Across all types, short latency responses are mostly evoked by L/M-opponent inputs whereas longer latency responses are evoked mostly by S-opponent inputs. Furthermore, neurons with late S-cone inputs exhibit dynamic changes in the sharpness of their chromatic tuning over time. We propose that the sparse, S-opponent signal in the lateral geniculate nucleus is amplified in area V1, possibly through recurrent excitatory networks. This results in a delayed, sluggish cortical S-cone signal which is then integrated with L/M-opponent signals to rotate the lateral geniculate nucleus chromatic axes.

Neural dynamics for facial threat processing as revealed by gamma band synchronization using MEG

“…In line with previous findings, our MEG-SAM results showed significant gamma band synchronization in occipitotemporal cortex. We found that visual ERS occurred as early as around 20-50 ms after stimulus onset, a time-range consistent with previous reports on short visual latencies using single neuron recordings (Luck et al, 1997;Cottaris & De Valois, 1998;Tovee et al, 1993) and MEG/EEG methods (Braeutigam et a., 2001;Seeck et al, 1997). Our finding of significant ERS in the occipitotemporal cortex including the fusiform face area is also consistent with fMRI findings on face processing (Yovel and Kanwisher, 2004;Haxby et al, 2001).…”

Spatial and Temporal Properties of Cone Signals in Alert Macaque Primary Visual Cortex

“…The delay of the S-cone signal confirms the results of Cottaris and De Valois (1998) and provides a mechanism for the slightly longer reaction times to stimuli operating through the S-opponent versus L/M-opponent subsystems (Smithson and Mollon, 2004); moreover, the different timing of center and surround, coupled with the chromatically opponent rebound re- Figure 10. Spatiotemporal response of the cone inputs to a single cone-opponent neuron.…”

“…sponses (see below), likely accounts for the shifting color preferences over time of some neurons when they are tested with fullfield stimuli (Cottaris and De Valois, 1998). Finally, the timing differences of center and surround may help explain why doubleopponent neurons have been so resistant to study with drifting sine-wave gratings.…”

Blue-Yellow Signals Are Enhanced by Spatiotemporal Luminance Contrast in Macaque V1

“…Nonlinear color tuning has been documented in previous studies of V1 (Cottaris and DeValois 1998;DeValois et al 2000;Hanazawa et al 2000;Lennie et al 1990;Solomon et al 2004;Wachtler et al 2000). Modeling attempts, however, have focused on a restricted class of nonlinear models, that is: linear summation of cone inputs followed by a static nonlinearity (Eq.…”