Degree Name

Doctor of Philosophy


School of Psychology


In four studies, this thesis examined the effect of task difficulty and brief training on inhibitory processing in the Go/Nogo task, and transfer to the Stop-signal and Eriksenflanker tasks. It also aimed to clarify how the event-related potential (ERP) of the N2 and P3, as well as the earlier N1 and P2 components, reflect training-related modulations in the underlying neural processes. This was achieved by (1) the use of three task difficulty levels (Low, Medium, High) using incremental reaction time deadlines (RTDs), (2) the effect of these three RTDs on task performance and the early (N1, P2) and inhibition-related (N2, P3) ERP components after brief training, (3) the use of another form of task difficulty – stimulus prepotency – to investigate whether training effects may be enhanced, and (4) the use of single Go/Nogo training (planned inhibition) vs. combined training of Go/Nogo (planned inhibition) and Stop-signal (action cancellation) inhibition. The main results were that the Nogo N2 effect was robustly observed to increase with greater task difficulty (i.e. RTDs), but that it reduced irrespective with time-on-task or training condition. It does not appear to reflect neural processing related to motor or pre-motor inhibition, but may instead represent the detection of conflict between responses. The Nogo P3, however, behaved in a fashion consistent with an inhibitory interpretation, being reduced with greater task difficulty (concurrent with lower levels of task performance), but showing increased amplitudes over frontal brain regions with training and improved task performance – an effect that showed near-transfer to an untrained Stop-signal task. Reduced N1, but enhanced P2 amplitudes, occurred regardless of training condition, indicating a generalised change in sensory processing with repeated task administration. The results cast doubt on the current inhibitory interpretation of the N2. Instead they suggest that, not only does the amplitude of the frontocentral Nogo P3 represent neural processing related to inhibitory control, but that it shows clear training-induced quantitative changes coinciding with performance improvements - furthering both the theoretical and applied knowledge of the key task parameters required to effectively train inhibitory control.