INHIBITIONS OF RETURN: TWO INHIBITORY ORIENTING BIASES

Abstract

Inhibition of return (IOR) is an inhibitory aftereffect of visuospatial orienting, typically resulting in slower responses to targets presented in an area that has been recently attended. This thesis begins by briefly summarizing the phenomenon’s history, and describing work supporting the functional significance of IOR as a foraging facilitator. Discordances in the literature with respect to mechanism are highlighted—in particular the lack of theoretical constructs that can consistently explain innumerable dissociations. Three diagnostics (central arrow targets, locus of slack logic and the psychological refractory period, and performance in speed-accuracy space) are summarized, and positioned relative to the theory that there are two forms of IOR—the form which is manifest being contingent upon the activation state of the reflexive oculomotor system. The input form, which operates to decrease the salience of inputs, is generated when the reflexive oculomotor system is suppressed; the output form, which operates to bias responding, is generated when the reflexive oculomotor system is not suppressed. This theory is then advanced in three empirical chapters. In Chapter 2, findings from two experiments converge to support the hypothesis that the output form is operating at a post-perceptual stage of processing. Chapter 3 contrasts the two forms in a paradigm that intermixed two perceptual diagnostics. The findings support the conclusions from Chapter 2 for the output form, whereas the input form is shown to delay the rate of information accrual at the cued location. In Chapter 4, arrays of multiple cues were used to explore the effect of the centre of gravity of the cueing array when the two forms were generated. The findings suggest the time course of centre of gravity effects may be contingent upon task demands, in addition to the form of IOR that is generated. In Chapter 5, the findings presented in the thesis are summarized and synthesized with the literature, and contextualized relative to a computational process model representing the two forms. On balance, the research presented here provides strong support for the proposal that there are two forms of IOR: one affecting information accrual, the other affecting response thresholds.