Episodic retrieval and feature facilitation in intertrial priming of visual search

Huang, Holcombe, and Pashler (Memory & Cognition, 32, 12-20, 2004) found that priming from repetition of different features of a target in a visual search task resulted in significant response time (RT) reductions when both target brightness and size were repeated. But when only one feature was repeated and the other changed, RTs were longer than when neither feature was repeated. From this, they argued that priming in visual search reflected episodic retrieval of memory traces, rather than facilitation of repeated features. We tested different variations of the search task introduced by Huang et al., with the aim of uncovering when priming is episodic and when feature based. We found that varying the signal strength of target against distractors had a strong effect on the priming pattern. In difficult search with low signal-to-noise ratios of target against distractors, the priming patterns were episodic. When feature contrasts between target and distractors were increased, priming of different features was independent and additive. Our results suggest that, during inefficient search,priming can be episodic but that, for more efficient search, priming from different features occurs independently. The results support two-stage (or multistage) accounts of priming in visual search.