Degree Name

Doctor of Philosophy


School of Psychology


The early work of Sokolov established the phasic orienting reflex (OR) as primarily associated with changes in stimulus novelty – ‘newness’ per se. Novelty has been operationalised as reducing over re-presentations of the same innocuous stimulus (producing a lessening in response magnitude) and increasing for a changed stimulus. The OR is also sensitive to intensity and Significance (conferred by verbal instructions, “Significance” is capitalised in this thesis to distinguish it when it refers to a factor). Sokolov focused on stimulus-response patterns of autonomic measures. These measures were described as covarying, yet were found in subsequent Western work to fractionate. Only skin conductance response (SCR) demonstrated sensitivity to novelty, intensity, and Significance. Preliminary Process Theory (PPT) was proposed to accommodate these fractionating measures. PPT outlines sequential stages of processing leading to the generation of the OR. Previous research has linked various autonomic measures and EEG alpha desynchronisation to specific processing stages. Sokolov had contended that the phasic OR is linked with all the major systems of the body, so event related potentials (ERPs) should also be linked to OR-associated processing. Here, four studies employed innocuous auditory stimuli of moderate intensity, rise/fall times, and very long interstimulus intervals (ISIs). Single-trial autonomic and ERP time-locked data were collected concurrently, enabling direct comparisons of autonomic and central measures. Manipulation of novelty within subjects was common in all the studies. Temporal Principal Components Analysis decomposed ERPs into components that constituted central dependent variables. When an aspect of the stimulus-response pattern for a measure differed from SCR, that difference was statistically tested. Study 1 varied novelty within subjects solely; SCR, cardiac deceleration (ECR1), respiratory pause (RP), and ERPs were dependent measures. Study 2 varied intensity between subjects; intensity-sensitive Peripheral Vasoconstriction (PVC) was included. Study 3 varied Significance within subjects, and Significance-sensitive cardiac acceleration (ECR2) replaced PVC. Summary Study 4 extracted data from the previous studies, combining it to increase power in an attempt to resolve cases of ‘no difference’ between a measure and SCR for habituation-based results; Processing Negativity (PN) was included to resolve inconsistent decrement findings. Elicitation of P3a prior to P3b and Novelty P3 (nP3) affirmed the independence and latency order of these Late Positive Complex (LPC) subcomponents. No single ERP matched the stimulus-response pattern of the SCR, which exhibited all aspects of the OR. The assessed measures were integrated provisionally into PPT. The data support ECR1, P1, N1-3, and PN as indexing stimulus registration; RP and nP3 as indexing novelty registration; PVC and P3b as indexing magnitude registration; and ECR2 and SW as matching the Response system. Finally, the LPC was assigned as the central analogue for the phasic OR. Further work is needed to explore dishabituation processes with respect to habituation criteria. Examination of the functional roles of the ERP components showing ambiguous results in the stages of processing may clarify their placement in PPT. Investigation into the neural substrates underlying stages of processing in PPT would be beneficial for PPT’s advancement. Finally, the expansion of PPT into other modalities and clinical applications is advocated.