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Maria Lev, Uri Polat; When simultaneous presentation results in backward masking. Journal of Vision 2010;10(7):1365. doi: 10.1167/10.7.1365.
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© ARVO (1962-2015); The Authors (2016-present)
Collinear facilitation is an enhancement in the visibility of a target by laterally placed collinear flankers (COL). Non-collinear configuration (parallel, side-by-side, SBS) produces less facilitation. Surprisingly, presentation of COL and SBS configurations simultaneously (CROSS) abolishes the facilitation rather than increases it - a phenomenon that has not been well understood. Here we directly explored the effect of canceled facilitation in the CROSS configuration. We used a Yes/No detection task measuring the hit-reports (Phit) and the false-positive-reports (false-alarm, Pfa) for a low-contrast Gabor target embedded between flankers. We compared COL, SBS and CROSS configurations. We also recoded Evoked Responses Potentials (ERP) from the occipital cortex. The results show that Phit were higher for COL and SBS, but decreased for the CROSS configuration. Pfa were also the lowest for the CROSS configuration. Thus, the decision criterion switched from target present (Yes) in COL to target absent (No) in CROSS, reminiscent of our earlier results of suppression by backward masking. However, the amplitude of the P1 ERP component (reflecting the strength of stimulation) is not reduced for the CROSS configuration – opposing the possibility of lateral inhibition between flankers. The amplitude of the N1 component, a marker of lateral interactions, is in correlation with the reduction in collinear facilitation in the SBS configuration. Thus, the ERP results show that the abolished collinear facilitation in the CROSS is not due to lateral inhibition between the COL and the SBS flankers. Interestingly, the latency of SBS is delayed by about 10 ms compared to COL, suggesting that the facilitatory process is selectively canceled due to backward masking effect by the delayed signal from the SBS. Thus, perceptual advantage of collinear facilitation may be lost when interfered with facilitation from the sides, whereas the final perception is determined by the overall spatial-temporal integration of the lateral interactions.
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