MEG analysis of contrast gain and temporal summation property of human red-green opponent system

摘要

The purpose of this study was to investigate the cortical processes which are involved in the human red-green opponent system by using the technique of magnetoencephalography (MEG). For this purpose, visually evoked magnetic responses to isoluminant red-green chromatic gratings presented in the lower-right visual field were recorded as functions of chromatic contrast and exposure duration of the stimulus with spatial frequency as a parameter. The magnetic responses to the chromatic stimuli consisted of two major components: an early component with its peak at around 100 ms and a late component with its peak at around 150 ms. The early component grew more rapidly with increasing the chromatic contrast or exposure duration of the stimulus than the late component did. Further, the peak latency of the early component varied to a less degree with change in the chromatic contrast or exposure duration than that of the late component. Current source localization with a single dipole model indicated that the early component originated from the cortical activity in V1/V2, while the late component from the cortical activity in the anterior-ventral area relative to V1/V2. The distinctive stimulus dependencies of the early and the late components together with the results of the current source analysis, suggest that the human red-green opponent system is composed of hierarchical cortical processes through which stimulus chromatic information is transformed successively from the lower to the higher levels of neural representation.