Degree Name

Master of Science (Honours)


School of Psychology - Faculty of Health & Behavioural Sciences


This thesis involves two studies using a warned visual Go/NoGo task. The first study investigates the effect of the late contingent negative variation (CNV) on the following post-stimulus event related potentials (ERPs), the N2 and P3, and the following study examines the relationship between the N2, P3 and inhibition.

In an S1–S2 Go/NoGo task the impact of slow potentials following S1, particularly the late component of the CNV, on the following cognitive-processing waveforms to S2 (e.g., N2 and P3) remains unclear. A common method to correct for these confounding slow waves employs a baseline set shortly before S2. The impact of this on ERP measures relating to S2 is debatable. An earlier method of CNV correction, devised to remove its effect on P3 measures by using different baselines for each condition, appears questionable. The first study explored the removal of the CNV from both Go and NoGo waveforms to clarify the sensory and cognitive components elicited by S2. Fifty three undergraduate students participated in the study, with forty of these used as subjects in the final analysis. Principal Components Analysis (PCA) was performed on the ERP means, and a component relating to the CNV was subtracted from each subject’s raw data for each site and condition. Results showed that this effectively removed the CNV without distortion of the S2 ERP morphology. This technique may prove useful in the analysis of the N2 and P3 as indicators of processes involved in response inhibition.

The aim of the second study was to investigate the relationship between the NoGo N2 and the NoGo P3 ERP components with inhibition in social drinkers, using a visual Go/NoGo task. The forty participants from study 1 were divided into three groups on the basis of their level of alcohol consumption. The two extreme groups, Light and Heavy, each with 13 subjects, were selected for the study. While impaired control over drinking was found in the Heavy group, there were no group differences in anxiety, depression, or locus of control. The Go N2 was slightly smaller centrally and in the midline for the Heavy compared to the Light group, while the Go P3 showed no group differences. The NoGo N2 was slightly smaller centrally, and the NoGo P3 was globally much smaller, in the Heavy group. Only the NoGo P3 reduction was correlated with alcohol consumption. That is, the NoGo P3 was the ERP component reflecting heavy social drinking.

However, this could not be considered as a marker of inhibition deficits, as the groups had similar performance levels in the task. Further consideration of the literature indicated that this is generally compatible with performance results in other studies that have attributed NoGo P3 differences to inhibition deficits, casting doubt on that interpretation. An alternative interpretation in terms of the orienting reflex (OR) is offered. This suggests that individuals with impairments in basic aspects of reflexive OR functioning may be prone to risk-taking behaviours, such as those associated with alcohol/drug abuse.

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