Representation, focus, and movement of covert visual attention
This thesis investigated some of the factors involved in the representation, focus, and movement of covert attention in visual space. Existing research has shown that visual cues produced a facilitation of reaction times (RTs) to visual targets appearing at a cued location for up to 300ms. At longer stimulus-onset-asynchronies (SOAs), this was followed by an increase in RTs relative to the uncued location. This has been termed inhibition of return (lOR). Experiments 1-6 used LED cues which were the same as, or spatially distinct from, a target LED, and were either informative or uninformative about the target location. Results were inconsistent. Where discrimination problems existed, the cue/target probabilities altered the results: from evidence of inhibitory effects, to no significant cue-side effects. Where no discrimination problems existed, facilitatory effects were apparent, and were enhanced by an increased cue/target probability. Experiments 7-10, using exogenous cueing, manipulated attentional focus and the presence of cue-markers. Altering the focus size did not substantiate previous findings of a reciprocal relationship between focus and performance. The removal of cue-markers resulted in increased amounts of inhibition not supporting current single- or dual-component views of lOR. Previous work has shown that informative symbolic visual cues produced costs and benefits of RTs to visual targets. Experiments 11-16, using static endogenous cueing with targets framed in central and peripheral locations, attempted to demonstrate object-based attentional representation. All six experiments showed significant effects due to SOA and cue validity, however, initial results showed no evidence of stimulus-grouping. Only when target position markers were removed, when peripheral targets were used, and when inside/outside location judgements were required instead of target detection, did results indicate some possibility of grouped attentional representation. Finally, several of the experiments also investigated the nature of attentional movement. Results did not support straightforward analogue explanations.