A study of relationship between multifocal VEF responses and binocular disparity.

Multifocal visual evoked magnetic field (mfVEF) is useful for shortening the measurement time and/or improving the signal-to-noise ratio of recording, in investigating cortical activities elicited by multiple stimulus patches across the visual field. To record the whole-head mfVEF, we previously developed custom software to deliver multifocal stimuli and to analyze the acquired data, and we applied it to investigation of stereopsis. In the present study, relationship between mfVEF responses and binocular disparity was investigated. Subjects were instructed to fixate a nonius line in the center of a screen, and they were presented with rapid alteration of random-dot (RD) patches. The experiments consisted of a luminance change condition (condition L) and seven binocular disparity conditions (condition BDs) ranging from a crossed disparity of 1 deg to an uncrossed disparity of 1 deg. Each response evoked by one of the RD patches was obtained with the multifocal technique. Although all subjects showed obvious responses in the condition L, only one of the subjects showed obvious responses in condition BDs. The sources of the responses recorded in condition BDs were mainly localized around calcarine sulci according to the known retinotopic cortical representation. The responses obtained in condition BDs showed dependence on binocular disparity in the magnitude and the latency. These results would be the basis for further analysis of brain magnetic responses related to stereopsis.