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Anna Sterkin, Oren Yehezkel, Yoram Bonneh, Anthony Norcia, Uri Polat; Multi-component correlate for lateral collinear interaction in the human visual cortex as revealed by Visual Evoked Potentials. Journal of Vision 2007;7(9):598. doi: https://doi.org/10.1167/7.9.598.
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© ARVO (1962-2015); The Authors (2016-present)
The perceptual effect of facilitation during lateral masking, measured as a decrease in detection thresholds for low-contrast Gabor patches (GP) when flanked by collinearly oriented high-contrast patches was previously reported. However, earlier studies of long-range spatial interactions in human visual cortex either performed spectrum analysis or focused on the waveforms for perifoveal target stimuli with contrast pedestals.
Here, visual evoked potentials (VEPs) elicited by a foveal near-threshold target GP presented in isolation (T), T in the presence of two flanking collinear high-contrast GPs (lateral masking, LM), or the flankers alone (F) were measured. The paradigm was compatible with the behavioral facilitation of T detection. Both waveform and spectrum in the 1 to 10 Hz frequency band for the midline occipital site were analyzed.
When LM was compared to linearly summed waveforms elicited by T and F, significant attenuation of peak amplitudes was found for each of five components, ranging between 64–290 ms after stimulus onset. In order to assess the effect of lateral interactions, the ratio between the spectrum amplitude of the linear prediction and LM was calculated. Suppression peaked at 1Hz (0.5 log units) and dropped to zero at 4Hz, followed by facilitation at higher frequencies (5–8Hz, peak at 6 Hz, 0.4 log units).
Despite the fact that the waveform elicited by LM was largely dominated by the high-contrast flankers with no differences in the latencies of any component, lateral interactions were reflected by nonlinear waveform modulations of multiple components and frequencies, including early onsets. Moreover, the spectrum analysis suggests that the perceptual outcome reflects a combination of shifting modulation distributed at different frequencies, either suppression or facilitation. Thus, the physiological correlates of lateral interactions may originate at multiple sources, while their impact on the perceptual decision is imbalanced.
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