Dynamics of perceptual learning in visual search

The present work is concerned with a phenomenon referred to as contextual cueing. In visual search, if a searched-for target object is consistently encountered within a stable spatial arrangement of distractor objects, detecting the target becomes more efficient over time, relative to non-repeated, random arrangements. This effect is attributed to learned target-distractor spatial associations stored in long-term memory, which expedite visual search. This Thesis investigates four aspects of contextual cueing: Study 1 tackled the implicit-explicit debate of contextual cueing from a new perspective. Previous studies tested explicit access to learned displays by applying a recognition test, asking observers whether they have seen a given display in the previous search task. These tests, however, typically yield mixed findings and there is an on-going controversy whether contextual cueing can be described as an implicit or an explicit effect. The current study applied the new perspective of metacognition to contextual cueing and combined a contextual cueing task with metacognitive ratings about the clarity of the visual experience, either of the display configuration or the target stimulus. Bayesian analysis revealed that there was an effect of repeated context on metacognitive sensitivity for configuration, but not target, ratings. It was concluded that effects of contextual memory on metacognition are content-specific and lead to increased metacognitive access to the display configuration, but not to the target stimulus. The more general implication is that from the perspective of metacognition, contextual cueing can be considered as an explicit effect. Study 2 aimed at testing how explicit knowledge affects memory-guided visual search. Two sets of search displays were shown to participants: explicit and implicit displays. Explicit displays were introduced prior to the search experiment, in a dedicated learning session, and observers should deliberately learn these displays. Implicit displays, on the other hand, were first shown in the search experiment and learning was incidental through repeated exposure to these displays. Contextual cueing arising from explicit and implicit displays was assessed relative to a baseline condition of non-repeated displays. The results showed a standard contextual cueing effect for explicit displays and, interestingly, a negative cueing effect for implicit displays. Recognition performance was above chance for both types of repeated displays; however, it was higher for explicit displays. This pattern of results confirmed – in part – the predictions of a single memory model of attention-moderated associative learning, in which different display types compete for behavior and explicit representations block the retrieval of implicit representations. Study 3 investigates interactions between long-term contextual memory with short-term perceptual hypotheses. Both types of perceptual memory share high similarities with respect to their content, therefore the hypothesis was formulated that they share a common memory resource. In three experiments of interrupted search with repeated and non-repeated displays, it was shown that contextual cueing expedites performance in interrupted search; however, there was no interaction of contextual cueing with the generation or the confirmation of perceptual hypotheses. Rather, the analysis of fixational eye movements showed that long-term memory exerts its influence on search performance upon the first glance of a given display, essentially affecting the starting point of the search process. The behavior of approaching the target stimulus is then a product of generating and confirming perceptual hypotheses with these processes being unaffected by long-term contextual memory. It was concluded that long-term and short-term memory representations of the same search display are independent and exhibit additive effects on search performance. Study 4 is concerned with the effects of reward on perceptual learning. It was argued that rewarding repeated displays in a contextual cueing paradigm leads to an acceleration of the learning effect; however, it was not considered whether reward also has an effect in non-repeated displays. In these displays, at least the target position is kept constant while distractor configurations are random across repetitions. Usually this is done in order to account for target position-specific probability learning in contextual cueing. However, it is possible that probability learning itself is modulated by reward. The current experiment introduced high or low reward to repeated and importantly, also non-repeated displays. It was shown that reward had a huge effect on non-repeated displays, indicating that rewarding certain target positions, irrespective of the distractor layout, facilitates RT performance. Interestingly, reward effects were even larger for non-repeated compared to repeated displays. It was concluded that reward has a strong effect on probability-, and not context learning