Visual evoked potentials to dynamic random-dot stereograms-the influence of visual field location, disparity and interocular correlation on latency

Latency period of visual evoked potentials (VEP) induced by dynamic random-dot stereograms (RDS) is indicative of process of visual depth perception. The authors examined effects parameters of RDS on the time course of VEP at various brain regions, and found that the waveforms can vary in three criteria: 1) negative response at the occipital region which starts at about 100 ms. 2) negative response occurring over the occipital and occipitoparietal region with latency period of 200~350 ms, and 3) positive response at the occipitoparietal region with latency period of 300~500 ms. The first response is likely to be attributable to a local disparity detection process, because it is localized at the occipital region. The start time of this response was constant regardless of stimulus parameters. On the other hand, the latency periods of the second and third responses to stimuli in the center field were shorter than those in the peripheral. Also, latencies to stimuli of crossed disparity were shorter than those of uncrossed disparity. Analysis of the delay with disparity to anticorrelated RDSs indicates that second and third responses reflect processing of binocular visual information including global stereopsis