Spatiotemporal properties of multiple-color channels in the human visual system.

Psychophysical and neurophysiological evidence argues for neural channels in V1 selectively sensitive to intermediate hues between the cardinal axes of opponent-color space. The present study examined if these multiple-color channels are selective for other visual features analyzed by V1 such as orientation, spatial frequency, and motion direction. Using a conventional masking paradigm, we measured detection thresholds for an isoluminant grating modulated along a particular hue angle either in the presence or absence of a bandpass noise mask that varied in hue angle, orientation, spatial frequency, and motion direction. In line with previous studies, thresholds for the test grating were selectively elevated by noise masks with hue angles similar to that of the test. Hue-selective masking was substantially reduced if test and mask were oriented orthogonally or differed in spatial frequency, but thresholds remained elevated if the mask drifted in the direction opposite to that of the test. Masking also revealed components selective for hue angle, but not for orientation. The results support the notion that multiple-color channels partly involve visual units selective for orientation and spatial frequency but largely nonselective for motion direction.