No oblique effect in chromatic pathways*

The classical oblique effect appears in flicker thresholds for luminous-contrast gratings at all temporal frequencies, but is absent in flicker thresholds for chromatic (red/green) gratings that are coarse enough to be fully resolved by the opponent-color pathways. This result is consistent with the physiological finding that luminosity cells in the striate cortex are generally orientation selective, whereas opponent-color cells are not.