TEMPORAL-CHROMATIC INTERACTIONS IN LGN P-CELLS

We studied the interaction between the chromatic and temporal properti es of parvocellular (P) neurons in the lateral geniculate nucleus (LGN ) of macaque monkeys. We measured the amplitudes and phases of respons es to stimulation by spatially uniform fields modulated sinusoidally a bout a white point in a three-dimensional color space, at a range of t emporal frequencies between 1 and 25 Hz. Below about 4 Hz, temporal fr equency had relatively little effect on chromatic tuning. At higher fr equencies chromatic opponency was weakened in almost all cells. The co mplex interactions between temporal and chromatic properties are repre sented by a linear filter model that describes response amplitude and phase as a function of temporal frequency and direction in color space along which stimuli are modulated. The model stipulates the cone inpu ts to center and surround, their temporal properties, and the linear c ombination of center and surround signals. It predicts the amplitudes and phases of responses of P-cells, and the change of chromatic proper ties with temporal frequency. We used the model to investigate whether or not the chromatic signature of the surround in a red-green cell co uld be estimated from the change in the cell's chromatic properties wi th temporal frequency. Our findings could be equally well described by mixed cone surrounds as by pure cone surrounds, and we conclude that, with regard to temporal properties, there is no benefit to be gained by segregating cone classes in center and surround.