[The effect of attention on visual evoked potentials elicited by a newly designed stereogram]

To investigate whether the visual evoked potentials (VEPs) obtained by a newly designed stereogram were generated by some higher function like depth perception, we examined the effect of attention on the VEPs.

Eight subjects participated in the experiments. The VEPs were recorded according to the international 10/20 system. The stimulus consisted of circles with or without disparity presented on 4 locations around the fixation point, and they appeared in one of 3 patterns in random order when viewed through red/green spectacles 1. at the same distance as the fixation point, 2. in front of it, or 3. at the back of it. The near pattern was defined as the target. In Experiment 1, the subjects just fixated on the fixation point. In Experiments 2 and 3, they were required to respond to the target by pressing a button and counting the number (target discrimination task).

A scalp negative potential with a latency of 170-280 msec was elicited in the lateral occipital area. For each of the 3 patterns the amplitude was greater in Experiments 2 and 3 than in Experiment 1. In Experiments 2 and 3, stimuli with disparity resulted in larger amplitude than without disparity. The target stimulus also evoked larger potentials than non-target stimuli did, although no such effect was apparent in Experiment 1.

Attention, as well as disparity, increased the VEPs amplitude, which indicates that the potential could be generated by neural activity higher than V 1 including depth perception. Moreover, the potential showed characteristics similar to attention-related potentials modulated by visuo-spatial attention.