Degree Name

Doctor of Philosophy (PhD)


Department of Psychology - Faculty of Health & Behavioural Sciences


In five studies, this thesis examined inhibitory processing in the Go/NoGo task, during which participants were instructed to either execute or withhold a prepared response. These studies extended previous Go/NoGo research by investigating the relationship between prior response preparation and subsequent inhibitory processing, with the aim of clarifying the relationship between the N2 and P3 ERP components and inhibitory processing. This was achieved by (1) the use of a fixed foreperiod prior to the Go/NoGo stimulus, (2) the concurrent examination of other components related to stimulus perception (e.g., N1, P2, early CNV) and action (e.g., the late slow wave), (3) the use of both overt and covert responses, and (4) the use of informative cues to elicit differential preparation for a Go or NoGo stimulus. The main results were that a NoGo N2 effect can be robustly observed using auditory stimuli, but that the N2 does not appear to reflect motor or cognitive/pre-motor inhibition, or the detection of conflict between responses. The NoGo P3, however, behaved in a fashion consistent with an inhibitory interpretation, being increased following higher levels of preparation for a response, absent when no inhibition was required to NoGo stimuli, and increased over the brain region specifically involved in motor commands. The results cast doubt on the current inhibitory and conflict interpretations of the N2, and suggest rather that the P3 may represent an inhibitory process.

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