Year

2014

Degree Name

Doctor of Philosophy

Department

School of Psychology - Faculty of Social Sciences

Abstract

A large portion of the event-related potential (ERP) oddball task literature, and associated theoretical development, has focused on context-related manipulations, and somewhat overlooked the temporal determinants of ERP components. The overarching aim of this doctoral thesis was to explore the mechanism underlying the systematic increases in amplitude, and decreases in latency, of the P300 ERP component that are observable when the interval separating presentations of matching stimuli is increased (target-to-target interval, TTI; nontarget-to-nontarget interval, NNI). This body of work suggests that the mechanism is operational on both target and (sometimes) nontarget events at specific processing stages. Support was evidenced for a memory-trace mechanism, however findings argued against a global refractory period effect. Three paradigms were utilised: a visual (Study 1) and an auditory (Study 5) fixed-ISI three-stimulus oddball task, and a unique auditory variable-ISI equiprobable Go/NoGo task (Studies 2, 3, and 4). In both Studies 1 and 2, increases in the TTI systematically enhanced target P300 amplitude. However, increases in the NNI augmented nontarget P300 amplitude in the equiprobable task (Study 2) only, suggesting that NNI effects in the nontarget P300 are apparent only under certain conditions. Study 3 examined the memory-trace mechanism and demonstrated that participants with high working memory (c.f. low working memory) ability showed a greater increase in target P3b amplitude with TTI increments, indicating a direct link between TTI effects in the target P300 and WM processes. Together, Studies 4 and 5 showed that matching-stimulus intervals modulated N1, P2, mismatch negativity (MMN), P3a, and P3b, but not Processing Negativity (PN), Novelty P3, and Slow Wave (SW), which suggests that a similar mechanism is operating on separate stages of stimulus-processing. In addition, regression analyses showed that early ERP components did not predict TTI/NNI effects in the P300, arguing against a global refractory period phenomenon, but possibly indicating memory-updating processes, or very long component generator recovery cycles. This thesis makes an important contribution by highlighting the circumstances in which the mechanism of matching-stimulus interval effects operates. Further work is required to separate a memory-trace mechanism from a very long recovery cycle phenomenon.

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