The Electrophysiological Markers of Statistically Learned Attentional Enhancement: Evidence for a Saliency Based Mechanism
It has been well established that attention can be sharpened through the process of statistical learning - whereby visual search is optimally adapted to the spatial probabilities of a target in visual fields. Specifically, attentional processing becomes more efficient when targets appear at high relatively to low probability locations. Statistically learned attentional enhancement has been shown to differ behaviorally from the more well studied top-down and bottom-up forms of attention; and while the electrophysiological characteristics of top-down and bottom-up attention have been well explored, relatively little work has been done to characterize the electrophysiological correlates of statistically learned attentional enhancement. In the current study, EEG data was collected while participants performed the additional singleton task with an unbalanced target distribution. Encephalographic data was then analyzed for two well-known correlates of attentional processing - alpha lateralization and the N2pc component. Our results showed that statistically learned attentional enhancement is not characterized by alpha lateralization, thereby differentiating it from top-down enhancement. Yet targets at high probability locations did reliably produce larger N2pc amplitudes, a known marker of increased bottom-up capture due to higher target-distractor contrasts. These results support an interpretation of the probability cuing effects where the improved processing of targets at expected locations is mediated by a saliency-based mechanism - boosting the salience of targets appearing at high-probability locations relative to those at low-probability locations. Significance statementThings are easier to find when you have a good idea of where they should be - e.g. shoes on the floor and birds in the sky. Expectations of where things are likely to be found can be implicitly learned without much, if any, awareness. Until now, little was known about how these implicit spatial biases change the representation of items in the brain. In the current work, we present EEG recordings which suggest that the brain may represent items in common locations as more salient than in other locations in space. These findings inform how the brain represents implicit search expectations; supporting a model where items in expected areas in space capture attention more frequently because they are represented by the brain as more salient.