Abstract
Visual search for a conjunction target is greatly facilitated by giving observers a preview of half the distractors before the target and the remaining items appear1. Previous studies have shown that this preview advantage in search is diminished if participants engage in a secondary task when the preview is present2. Here we examined the effects of different secondary tasks, contrasting verbal and spatial memory loads. Both forms of memory load decreased search efficiency in preview search compared with baseline (no preview) search conditions, but the effects of the spatial load were more severe and, unlike the verbal load, did not diminish by given observers more time to encode the pattern. The data indicate that preview search is modulated by spatial memory for the first set of distractors, consistent with the idea that search is made efficient by inhibitory visual marking of a memory representation of the old items1. Other accounts of preview search fail to explain these selective interference effects.
1. D. G. Watson and G. W. D.G. Humphreys. (1997). Visual marking: Prioritising selection for new objects by top-down attentional inhibition. Psychological Review, 104, 90-122.
2. G. W. Humphreys and D.G. Joliceour. (2002). Fractionating visual marking: Dual task decomposition of the marking state by timing and modality. Journal of Experimental Psychology: Human Perception and Performance, 28, 640-660.