Top-down and exogenous effects on covert and overt orienting

Due to numerous bottlenecks, the human brain is unable to consciously process all data available at the retina. To overcome these constraints, evolution has developed a system that breaks down retinal information into fragments and subsequently analyses them according to current goals and expectations. This biasing system is frequently referred to as attention. Yet despite a long history of itself having been the focus of analysis, there are a number of questions about attention that are clearly unanswered by the literature. Therefore, we wanted to address three problems highlighted by our literature review. Specifically, we wanted learn, (I) Are the effects of probabilistic expectations, when instructed either by spatial blocking of the target location or through a central cue, on response latencies the product of a ballistic, attentional process, or the product of an information theoretical decision-making process? (II) Can the inhibitory aspects of spatial attention be pre-deployed by using a central cue to manipulate prior expectations of where a task-irrelevant distractor is likely to appear? (III) What is the relationship between attention and eye movements?We investigated this last question by way of testing healthy participants on covert and overt versions of the behavioural paradigms designed to address questions I and II, and then in a neuropsychology patient who presented with hypometric saccades, we investigated if eye movements and attention can be dissociated. Experiments 1-4, showed that the effects of target probability - when either spatially manipulated or instructed through a central cue - can neither be fully accounted for by attentional accounts or information theoretical accounts. Additionally, the outcome of target probability is context dependent. That is, outcomes depend on how target probability was instructed. Experiment 5 showed that spatial inhibition cannot be endogenously deployed using central cues. Although we found that distractor suppression takes place when targets are invalidly cued, suggesting distractor suppression takes place during reorienting. Experiments 6-7 showed that attentional orienting can be preserved in the presence of oculomotor impairment, indicating eye movements and attention can be structurally dissociated. Whereas the results of experiments 1-5 are consistent with claims that covert and overt orienting are similarly affected by expectations due to a common attentional process. We conclude that expectations influence a mechanism common to overt and covert responses, but ultimately, both processes are distinct. In the discussion chapter, we discuss a number of future avenues of research,including how electrophysiology could be used to further understand the phenomena presented here. Overall, the contribution of this body of research is to illustrate that the relationship between top-down expectations and exogenous effects is extremely complicated, and are, currently, inadequately captured by present models of attention.