Perceptual learning induces active suppression of physically nonsalient shapes

: Visual attention can be attracted by salient-but-irrelevant features, a phenomenon called attentional capture. Accompanying attentional capture, a top-down inhibitory mechanism is usually enacted to suppress the attentional shift. Our recent study showed that a physically nonsalient shape, which may be considered as a conjunction of basic features within the form domain, can also provoke a robust capture of attention as a consequence of perceptual learning, supporting an important role of prior experience in attentional deployment. It remains unclear, however, whether prior experience can also induce attentional suppression to conjunctions of features. Here, we examine whether and in which condition the brain would initiate an active suppression process to a physically nonsalient shape which has acquired an ability to capture attention after perceptual learning. We show that detectability of a shape after perceptual learning may be a key factor determining whether the shape would be actively suppressed or not. After extensive training as a target in visual search, a physically nonsalient shape could elicit an N2pc component when it was a distractor in a visual search task or a peripheral irrelevant stimulus in a central focused attention task, indicating a capture of attention induced by perceptual learning. Following the N2pc component, a Pd component would be elicited by the trained shape only if its detectability is relatively high. These findings suggest that an active suppression process could be applied not only to salient features but also to physically nonsalient shapes. A physically nonsalient shape could improve its salience through perceptual learning and would be actively suppressed when its learned salience reaches a certain level.