Abstract
[Background] It has been suggested that the higher order color mechanism consists of multiple channels, but the precise of the channels are unclear. On the other hand, color stimulus with a certain range of hue to adapt a channel, for example, yields opposite hue appearance according to color-constancy mechanism. This is not the best method to investigate the characteristics of multiple-channel systems.
[Methods] Notched-noise adaptation technique has been often used to study multiple-channel mechanisms in visual system. We modified dynamic random-color-mosaic pattern (20 frames/s) to produce a chromatic notched-noise stimulus by eliminating a certain range of hue from the colors in the mosaic pattern. The channels sensitive to the hues presented in the stimulus will be desensitized by adaptation, but the sensitivity of channels with selectivity in the direction of “notch” will be retained. Afterimage from this notched-noise stimulus is expected to reveal the characteristics of the channels. We varied the direction and the range of the notch in a cone-contrast color space. The afterimages were measured by the method of adjustment.
[Results & Discussion] All subjects perceived chromatic afterimages, when a uniform gray field was presented immediately after the adaptation. The afterimage had roughly same hue as the direction of notch, but there were systematic deviations. This systematic deviation was common to all subjects, and was not found after adaptation to a uniform color field with a mean chromaticity of the notched noise. We examined a simple computational model to account for this hue deviation in the notched-noise adaptation afterimages. The model analysis revealed that at least five channels are necessary to account for the data. Also, the hue selectivity of each channel was estimated.
[Conclusion] The use of dynamic color-notched-noise stimulus is an effective method to investigate the characteristics of multiple-color mechanisms in the higher order human color vision.