Doctor of Philosophy
School of Psychology - Faculty of Health and Behavioural Sciences
Broyd, Samantha J, Electrophysiological correlates of interference control in the Eriksen task, PhD thesis, School of Psychology, University of Wollongong, 2008. http://ro.uow.edu.au/theses/363
This thesis examined conflict monitoring in the Eriksen task in which participants must respond to a centrally positioned target arrow and ignore simultaneously presented distractors that flank the target. Distractors were either associated with a response congruent to the target, in conflict with the target, or, in a neutral condition, not associated with a response, instead producing only perceptual interference. This thesis extended on previous Eriksen research by systematically investigating the effect of varying the level of response conflict and task difficulty on stimulus processing in six studies and clarifying the functional role of ERP components elicited in the Eriksen task. Specifically, this was achieved by (a) varying the number of flanking distractors and, (b) the level of response conflict by using different permutations of incongruent distractors, (c) reducing target stimulus perceptibility through degradation, (d) utilising both valid and invalid information to increase response preparation and make conflict monitoring more difficult, and (e) providing feedback in a speeded version of the task. In all six studies, two N2 components were clearly delineated – the first of which was increased to stimuli requiring enhanced feature detection processes (N2a), while the second N2 component (N2b) was consistently observed to increase following the detection of response conflict. The P3 component, rarely considered in the Eriksen paradigm, was reduced at parietal sites and increased in latency as the discriminability of the target amongst the distractors became more difficult. The results suggest that the P3 component may reflect stimulus evaluation processes and equivocation related to the ease of target identification and concurrent response selection processes imperative for accurate task performance. This thesis also utilised digital filtering to clarify time-domain ERP results in terms of the relative contributions of activity in the alpha, theta and delta frequency ranges. Event-related theta oscillations contributed significantly to the morphology of the two N2 components reflecting allocation of focused attentional resources following the detection of perceptual (theta N2a) or response conflict (theta N2b). Activity in both theta and delta frequency ranges was robustly observed to contribute to the P3 component. An increased theta response at frontal sites was observed along with increases in task difficulty likely indexing the activation of anterior attentional resources. The results also suggest that the parietal delta P3 component reflects a refined form of equivocation, sensitive to the perceptibility of the target, and concomitant with the relative ease of accurate response selection. This thesis has clarified successful conflict monitoring and task performance in the Eriksen task, and the relationship with stimulus-locked ERP components in the time and frequency domains. The results suggest that the second frontally maximal N2 component reflects successful conflict monitoring, while the P3 component most probably reflects equivocation arising from difficult target identification and accurate response selection, rather than response conflict per se.
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