Year

2011

Degree Name

Doctor of Philosophy

Department

School of Psychology

Abstract

In a series of four studies, relationships between the auditory evoked cardiac response (ECR) and event-related potentials (ERPs) were examined, in an attempt to identify similarities between measures found important in the autonomic orienting reflex (OR) context and the ERP literature. The phasic evoked cardiac response (ECR) produced by innocuous stimuli requiring cognitive processing may be described as the sum of two independent response components. An initial heart rate (HR) deceleration (ECR1), and a slightly later HR acceleration (ECR2), have been hypothesised to reflect stimulus registration, and cognitive load, respectively. Two ERP components consistently linked to the processes thought to be represented by the ECR, are the N1 complex and Late Positive Complex (LPC). Therefore, the ECR, and N1 and LPC ERP measures, were systematically investigated in this thesis using varying manipulations of stimulus intensity and cognitive load to elucidate these putative relationships, based on the association of the ECR with preliminary OR processes in Preliminary Process Theory (Barry, 1984a, 1987a, 1987b, 1996, 2006, 2009). As expected, the phasic ECRs observed throughout this thesis were multiphasic (deceleration-acceleration) responses, reflecting stimulus parameters and situational factors. Following the methodology of previous research, components of the ECR were operationally separated by using conditions varying stimulus significance, allowing relationships to be drawn between components of the ECR and individual aspects of stimulus processing (Barry, 1982, 1984; Barry and Tremayne, 1987). The ECR1 was observed to be relatively invariant to stimulus parameters, and was thus taken as an index of stimulus registration; the ECR2 was observed in tasks with stimulus significance (i.e. Count vs. No Count), and was interpreted as reflecting increased cognitive processing demands. For the N1 complex, stimulus intensity and minor cognitive load effects were observed, indicating this component is an unlikely index of stimulus detection/registration. However, the effects observed for the LPC indicate that this complex is closely associated with the processing indexed by the ECR2, and was supported by significant correlations between these two measures. In addition, a new cardiac response form was found which challenges the current interpretation of ECR2. This was unable to be explored here, but offers exciting perspectives for future work.

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