Abstract
Previewing one set of stimuli enables increased search efficiency through subsequently presented new items – the preview benefit (Watson & Humphreys, 1997). This benefit occurs with both symbolic (e.g., letters) and valenced facial stimuli (Blagrove & Watson, in press). When changes are made to symbolic previewed stimuli at the same time as new items are added, only those changes that are likely to be of behavioural relevance (e.g., changes to object identity) cause the old items to re-compete for selection with the new items. Other changes (e.g., color or luminance changes) appear to have no effect, and the previewed items remain suppressed (e.g., Watson, Humphreys, & Braithwaite, 2008). Previous work has shown that expression changes made to previewed faces also abolish the preview benefit, with no differential effects of change direction (i.e. neutral to negative or positive changes). In the current work, two experiments examined whether this disruption of the preview benefit was due to ‘low-level’ feature changes or ‘high-level’ changes in facial expression. This was achieved by changing the position, but not the shape of the mouth in the previewed faces, when the new faces were added – thus creating a physical change without an associated change in emotion. Under these conditions, we obtained a robust preview search benefit with both negative and positive valenced preview distractors, compared with a full element baseline condition in which all items appeared simultaneously. Thus, as might be expected from an ecological standpoint, changes in expression appear to be more effective than simple ‘low-level’ physical changes in causing previously suppressed faces to re-complete for selection. In addition, as in previous work with face stimuli, preview search remained less efficient than when only the new items were presented alone, suggesting that faces might be more difficult to suppress than less socially relevant stimuli.