Abstract
Brain magnetic responses were measured with a 64-channel MEG (magnetoencephalography) system while subjects were engaged in a button-press task in response to random-dot stereogram (RDS) stimuli in order to study the human brain activity related to the depth perception process with high time resolution. Reaction time (RT) was also measured to quantify the temporal properties of subjective depth perception simultaneously. The RDS stimuli were characterized by disparity changes in a rectangular region of the right visual field, and two types of RDS stimuli—crossed disparity stimulus (Stim-C) and uncrossed disparity stimulus (Stim-U) where the disparity changed respectively from zero to crossed and from zero to uncrossed—were used. The button-press task consisted of two conditions: one with the depth judgment of the RDS stimuli and the other without the depth judgment. For the former condition, the subjects had to judge whether the rectangular region appeared in front of (Stim-C) or behind (Stim-U) a screen before pressing a button. From the experimental results, the first MEG peaks were observed between 100 and 180 ms after the onset of the RDS stimuli, and the estimated sources during the latency range were mainly localized in the left occipital lobe. In the depth judgment condition, while the median RT for Stim-C was significantly faster than that for Stim-U, there was no significant difference in the latency of the first MEG peaks between the two RDS stimuli. These results suggest that the first MEG peaks arise from brain activity related to relatively lower visual information processing whose latency does not differ between the two RDS stimuli.
