Temporal dynamics of human color processing measured using a continuous tracking task

Abstract

We characterized the temporal dynamics of color processing using a continuous tracking paradigm by estimating temporal impulse response functions associated with tracking chromatic Gabor patches. We measured how the lag of these functions changes as a function of chromatic direction and contrast for stimuli in the LS cone contrast plane. In the same set of subjects, we also measured detection thresholds for stimuli with matched spatial, temporal, and chromatic properties. We created a model of tracking and detection performance to test if a common representation of chromatic contrast accounts for both measures. The model summarizes the effect of chromatic contrast over different chromatic directions through elliptical isoresponse contours, the shapes of which are contrast independent. The fitted elliptical isoresponse contours have essentially the same orientation in the detection and tracking tasks. For the tracking task, however, there is a striking reduction in sensitivity to signals originating in the S cones. The results are consistent with common chromatic mechanisms mediating performance on the two tasks, but with task-dependent relative weighting of signals from L and S cones.