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(13)　Depth Perception in Virtual Three Dimensional Space: An Eye Movement and VEP Study
　　　　　　　　　　11th European Conference on Eye Movements (ECEM11),P87,2001-8

　The authors report results obtained by a new experimental system that has been presented at ECEM10. This system, including Eye Mark Recorder and Liquid Crystal Glasses (LCG), enables us to record eye movements in virtual three-dimensional space. By our system, the difference in eye movements can be investigated during viewing of stimuli that contain either depth or not.
A picture for the left eye is displayed on the upper half of the CRT, and a picture for the right eye is displayed on the lower half. Each picture consists of two random dots patterns; one pattern is a large rectangle that has no visual disparity between upper and lower pictures. The other pattern is a small rectangle included in a large rectangle. These small rectangles have visual disparity between upper and lower pictures. Subjects recognize the small rectangle to be nearer or farther than the large rectangle through the LCG system.
Three types of virtual stimuli (zero disparity: flat, 10 pixels disparity: medium, 30 pixels disparity: near) were randomly displayed to each subject, and each eye movement was recorded by the system. Simultaneously, visual evoked potential (VEP) by the stimuli was recorded from 19-channel scalp electrodes.
Vertical and horizontal eye movements and vergence angles were tested among three virtual stimuli. The results of the test determined by the difference between each two mean values of vergence angles show differences at a significance level of 1% between the flat and the medium, between the flat and the near and between the near and the flat, respectively. The mean values of vergence angles were monotonously increased as expected. In cases of horizontal and vertical movements no significant differences were observed among the flat, the medium and the near stimuli.
By a multiple-dipole analysis using a PC-based equivalent current dipole source localization system (SynaPointPro Ver.1.0, GE Marquette), one of the dipoles was localized to MT area around 200 ms post stimulus and to the parietal lobe around 400 ms. The former finding agrees with the fact that a function of stereovision lies in MT area. The latter finding suggests that after MT brain activity occurs in the parietal lobe.