Enhancement and Suppression Draw on Separable Mechanisms

Traditional models of attention state that target enhancement and distractor suppression utilize the same underlying neural mechanisms, which would predict that the strength of enhancement should covary with the strength of suppression. Recent evidence at the group-level, however, suggests that enhancement and suppression mechanisms are separable. These findings would be further supported if the strength of enhancement and suppression varied independently across individuals. To examine this, however, requires reliable measures of individual differences of both effects. Here we investigate within-task reliability of individual-difference measures of target enhancement and distractor suppression using adaptations of Posner Cuing and Additional Singleton visuo-spatial search tasks. Exp.1 examined enhancement using endogenous cues and suppression using statistical learning. Exp.2 examined enhancement and suppression using statistical learning only. In these experiments we found reliable individual differences in enhancement using both spatial cues (validity effect) and statistical learning (frequency of target or distractor location). Individual differences in suppression using statistical learning, however, were not reliable. In Exp.3 colors and shapes changed randomly across trials, encouraging the use of singleton detection mode. Here, statistical learning yielded reliable individual differences for both target enhancement and distractor suppression. Furthermore, we found that the magnitude of target enhancement did not covary with the magnitude of distractor suppression across individuals. Together, these results demonstrate the utility of an individual-differences approach. We find that individual differences in spatial enhancement are consistently reliable across tasks. In contrast, spatial suppression is less reliable and highly contextual, and thus may fluctuate more within individuals due to additional factors (i.e., shifting strategy, recent experience). When experimental design constrains search strategy, however, individual differences in distractor suppression may be reliably measured. With reliable measures, we show a lack of covariance between enhancement and suppression, contrary to the traditional unitary models of attention.