Abstract
Our recent neurophysiological findings provided evidence for collinear facilitation in detecting low-contrast Gabor patches (GPs) and for the abolishment of these collinear interactions by backward masking (BM). It was suggested that the suppression induced by the BM eliminates the collinear facilitation. Moreover, our recent behavioral study showed that training on a BM task improves the processing speed. Here we applied perceptual learning on BM in a detection task that strengthens the facilitatory lateral interactions, in ten overnight sessions, in order to study whether reinforced facilitatory interactions can overcome the suppressive effects induced by BM. Event-Related Potentials (ERPs) were recorded before and after the training. Low-contrast, foveal target GP was simultaneously flanked by two collinear high-contrast GPs. In the BM task, another identical mask was presented at different time-intervals (ISIs). Before training, BM induced suppression of target detection, at the ISI of 50 ms, in agreement with earlier behavioral findings. This ISI coincides with the active time-window of lateral interactions. After training, our results show a remarkable improvement in all behavioral measurements, including percent correct, sensitivity (d′), reaction time and the decision criterion for this ISI. The ERP results show that before training, BM canceled the physiological markers of facilitation at the same ISI of 50 ms, measured as the amplitude of the negative N1 ERP peak (latency of 260 ms). After the training, the sensory representation, reflected by P1 peak, has not changed, consistent with the unchanged physical parameters of the stimulus. Instead, the shorter latency (by 20 ms, latency of 240 ms) and the increased amplitude of N1 represent the development of facilitatory lateral interactions between the target and the collinear flankers. Thus, previously effective backward masking became ineffective in disrupting the collinear facilitation. We suggest that perceptual learning that strengthens collinear facilitation results in a faster processing speed.
Supported by grants from the National Institute for Psychobiology in Israel, funded by the Charles E. Smith Family and the Israel Science Foundation.