Perceptual long-term memory in visual search

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In visual search, human performance relies on several different cues that can aid attention. One of these cues is contextual information, that is, the learned target-distractor arrangement (e.g., Chun, 2000; TICS 4: 170-178). In a standard contextual cueing search task, observers search for the target letter T (distractor letters L) and report its orientation (left- vs. right-oriented). In the repeated condition, the target-distractor arrangement is repeated across trials; in the non-repeated condition, only target, but not distractor, locations are repeated (this equates target location repetition effects between the two conditions). Typically, the repeated condition consists of a set of 12 different displays with a certain target-distractor configuration that is presented repeatedly throughout the course of the experiment. The standard finding is that reaction times (RTs) are faster for repeated than non-repeated displays, an effect which emerges after about 100 to 150 experimental trials (i.e., after 4-6 repetitions of each of the repeated displays). Typically, these findings are taken to mean that long-term memory for learnt target-distractor arrangements facilitates visual search. Interestingly, when observers are asked about repeated displays by means of a recognition test performed at the end of the search experiment, they only perform at chance level. This has led to the proposal that contextual cueing is supported by an implicit memory system (cf. Chun & Jiang, 2003; JEP:LMC 29: 224-234). However, more recent investigations of the cueing effect, including our own, found that the effect is due to only a very limited number of (4±2) repeated displays (Geyer, Shi, & Müller, 2010; JEP:HPP 36: 515-532). This means that rather than learning about all or most repeated displays, it seems that only a very small number of repeated displays contributes to the cueing effect. Further, when assessing contextual cueing and recognition performance concurrently, it was found that observers could tell apart repeated from non-repeated displays, at least some of the repeated displays (Smyth & Shanks, 2008; Schlagbauer et al. 2012). This means that the cueing effect is eventually supported by an explicit memory system. Given this, the main aims of the proposed research are (1) to investigate the conditions (factors) that modulate the learning of repeated search displays (experimental series 1, 2, 4, 5); and (2), to shed new light on the relation between the cueing effect and visual awareness (experimental series 3, 6). One important feature of all experiments is the analysis of the dependent variables (reaction times, recognition performance, oculomotor variables, electrophysiological measures) at the level of each of the repeated displays.