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Oren Yehezkel, Anna Sterkin, Yoram Bonneh, Anthony Norcia, Uri Polat; Spatio-temporal tradeoff in neural processing of backward masking as revealed by visual evoked potentials.. Journal of Vision 2007;7(9):599. doi: 10.1167/7.9.599.
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© ARVO (1962-2015); The Authors (2016-present)
We developed a new VEP paradigm for exploring backward masking (BM) in the human visual cortex. Low-contrast, foveal target Gabor patches (T) were masked by two collinear high-contrast Gabor patches, spatially separated from the target. The mask was presented at different ISIs after (1) target alone (BM-on-T) or 2) the target plus simultaneous collinear flankers (lateral masking (LM), BM-on-LM) placed at the location of the mask. The elicited responses for various BM combinations were compared within time-windows defined by the separate waveforms evoked by the target alone, mask alone and the LM combination at different ISIs. The amount of correlation between the waveforms and/or the amplitude modulation of different components was regarded as indicative of a BM effect. There was no evidence for BM of the response to the target in either condition (1) or (2) at ISI=50, due to the temporal integration of the responses elicited by target and mask. This is compatible with the behavioral finding of no suppression of target detection in BM-on-T and a lack of lateral facilitation in BM-on-LM. However, while the response to the mask in the BM-on-T condition remained unchanged, the mask response was suppressed in BM-on-LM but recovered at longer ISIs. Moreover, the waveform produced by subtracting the response to LM from the response evoked by BM-on-LM is highly similar to the response to target, but with the peak latency of mask. This suggests a mechanism of extended persistence of the target representation that could underlie behavioral facilitation in LM. In both conditions, while the peak latency could be predicted by linear summation of the separate responses at all ISIs, the amplitude did not follow the linear prediction. Thus, the results suggest that BM reflects complex neural processing of temporal order and saliency of each component. This research was supported by grants from the The National Institute for Psychobiology in Israel founded by The Charles E. Smith Family (UP and AS) and Israel Science Foundation (UP).
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