Abstract
In the visual search literature, it has generally been shown that positive spatial priming occurs when a target requiring a discrimination response is presented at the same location as the preceding target. Two recent findings, however, provide important qualifications to such spatial priming. First, although spatial priming may be found with manual discrimination keypress responses, eye movements to repeated locations are inhibited. Second, what have been interpreted as spatial priming effects may largely be due to response repetition, rather than location repetition. Thus, the long-assumed relationship between spatial priming and attention is actually quite unclear. To provide clarity to this situation, we used the N2pc – an electrophysiological index of attentional selection – to reveal the effect of target-location and response repetition on deployments of covert attention. To accomplish this, participants completed a compound visual search task known to yield spatial priming. Each search display consisted of four chipped diamonds forming an imaginary square, centred around fixation. The target was a colour singleton, presented amongst homogeneously-coloured distractors. Participants made two-alternative-forced-choice discrimination responses to the shape of the target. Both the target’s shape and location in the search array varied randomly across search displays. As expected, keypress response times (RTs) were faster when the target location repeated instead of switched, but this effect was qualified by the relationship with response repetition: there was a large priming effect if both response and target location repeated, but the priming effect disappeared when responses switched. Importantly, N2pc amplitudes were always reduced when the target location repeated, both when responses repeated and switched. These results suggest that, like overt orienting, covert deployments of attention are biased against a previously attended location, while RTs are facilitated by later decisional processes when the target location and response repeat.
Acknowledgement: Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to S. Ferber and J. Pratt and NSERC PDFs to H.E.P. Lagroix and M.D. Hilchey.