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Yoichi Miyawaki; Signal model of latency delay in visual evoked potential by binocular disparity. Journal of Vision 2004;4(8):196. doi: 10.1167/4.8.196.
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© ARVO (1962-2015); The Authors (2016-present)
This paper discusses that the plausible genesis of the delayed visual evoked potential by binocular disparity stimulus. Our past studies demonstrated that binocular disparity stimuli evoke two successive negative components on the occipital pole, whose latency is 150ms and 250ms respectively. Firstly we investigated a latency variation of these components in response to continuous change of binocular disparity sign and interocular correlation of dynamic random-dot stereogram, and observed that only the 2nd component, not the 1st component at all, delayed in peak latency (+25.1ms, p<0.01) when uncrossed or uncorrelated stimulus was given. Typical views of past studies focusing on the averaged response naively associate a delay in VEP latency with delay in the onset of specific neural processes; however, such an interpretation would be valid only if we can assume ideal evoked components with fixed-latency and —polarity in each single trial that undergo a uniform delay. Recent reports, on the other hand, suggest that such ideal components do not exist but phase modulation of background rhythmic EEG (e.g. alpha wave), having considered not stimulus-related, would be the source of observed evoked components (Makeig et al, 2002). Next we examined which signal model is likely in the case of VEP by binocular disparity stimulus. Using single trial EEG clustering technique, we observed that 1) signal power of the delayed VEP and background EEG didn't correlate positively, 2) trial groups of the lowest background EEG power could reconstruct the signal that was highly correlated with the delayed VEP, and 3) background EEG didn't show consistent intertrial phase-lock during the latency period of the delayed VEP. These results indicate that the delayed VEP by binocular disparity stimulus reflects not a delay in phase-locking latency of rhythmic activity but a delay in evoked response latency, suggesting neural mechanisms distinct in their dynamics in a global stereopsis level.
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