Temporal activation parameters of attentional templates for visual search

Abstract

Visual search is guided by attentional templates that are maintained in visual working memory (VWM) and are activated during search preparation. However, it remains unclear how VWM capacity and strategic control affect the formation and activation of multiple attentional templates. This thesis presents six electrophysiological experiments to investigate the temporal and organisational properties of template co-activation. Experiments 1-2 (Chapter 2) examined template activation patterns in fully predictable two-colour search and found evidence for strategic template switching. Importantly, colour switch costs were due to delays in activating the relevant colour template rather than interference from a previously used template. Experiments 3-4 (Chapter 3) increased VWM load and measured template activation patterns in three-colour versus one-colour search. Results showed that three colour templates were activated in parallel when search targets varied unpredictably, but task performance was nevertheless reduced in the three- as compared to the one-colour search. Consequently, when participants were given the opportunity to reduce VWM load by making the colour sequence fully predictable, they chose to switch between templates rather than activate them in parallel. Experiments 5-6 (Chapter 4) widened the scope by studying the content and attentional guidance in conjunction search when target were defined by features from two different dimensions (colour and shape). The experiments revealed that attentional templates contained separate features rather than integrated object representations and that guidance was feature-based accordingly. Overall, these experiments demonstrated that three and possibly even four feature templates can be activated simultaneously in preparation for search. However, such template co-activation leads to mutual inhibition reducing template activation levels and search efficiency. This research contributes significantly to our understanding of the temporal and organisational parameters of memory-guided attention.