Abstract
The responses of some V1 neurons change nearly linearly with cone contrast whereas other neurons respond non-linearly. We studied color-opponent V1 neurons using a novel reverse correlation procedure that permits identification and characterization of a wide class of non-linear neuron. Previously we reported that the responses of blue-yellow neurons were non-linear and could be modeled as the product of a full-wave rectified luminance signal and a half-wave rectified blue-yellow signal (Horwitz et al. 2002 Soc. Neurosci. Abs. 720.8). Here we consider the temporal relationship between these luminance and blue-yellow signals.
V1 neurons in awake, fixating monkeys were stimulated with randomly flickering colored checkerboard patterns. Stimuli preceding spikes were analyzed to assess stimulus selectivity. The average stimulus preceding a spike in blue-yellow neurons was, by definition, an increase in blue and a decrease in yellow. Principal components analysis on the ensemble of spike-triggered stimuli revealed a rectified luminance signal. Joint consideration of both response properties was consistent with a multiplicative interaction between luminance and blue-yellow inputs.
The luminance signal reached its maximum ∼10 ms before the blue-yellow signal. These results are consistent with the idea that luminance transients increase the response gain of blue-yellow V1 neurons after a brief delay. This enhancement may be related to psychophysical demonstrations that luminance transients facilitate color vision.