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Title: Event-related potential studies of prefrontal cortex contributions to episodic retrieval
Author: Cruse, Damian
ISNI:       0000 0004 2747 6607
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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Although the prefrontal cortex (PFC) is known to play roles in episodic memory retrieval, the specific processes it supports are not fully understood. The high temporal resolution of the event-related potential (ERP) technique provides one fruitful avenue for investigations of these processes. However, the PFC-supported retrieval operations that may be indexed by ERPs are currently under-specified. The work contained in this thesis is concerned with providing a more specific characterisation of PFC-supported processes that operate during episodic retrieval than is available currently. To this end, Experiments One to Three were designed in order to assess the likely functional significance of one known modulation which has been identified in ERP studies of episodic retrieval - the right-frontal ERP old/new effect. This effect is widely assumed to reflect activity generated within the PFC. Experiments Four and Five extended this work to related issues which arose as a result of the outcomes of the initial experiments. All five experiments reported in this thesis employed source memory tasks in which participants studied a list of words presented in one of two contexts (or sources). These words were presented visually in one of two colours in Experiments One, Two, Three, and Five (Visual condition), and were presented auditorily in a male/female voice in Experiments Four and Five (Auditory condition). At test, in all experiments, all studied words were presented visually in white letters intermixed with unstudied (new) words. For words judged to have been encountered previously (old words), a second judgment was required. In Experiments One and Two, this was a binary decision regarding the source in which the word had been previously presented (study colour). In Experiments Three, Four, and Five, a high/low source confidence rating was also made. For the right-frontal ERP old/new effect, strong evidence was provided in Experiments One and Two to rule out the potential contributions of three aspects of task design that may have contributed to disparate and seemingly contradictory findings in the published literature. These were: the presence/absence of copy cues at test, response requirements at test, and the difficulty of the retrieval task. Experiment Three was designed in order to test directly a "number of decisions account" for the right-frontal old/new effect (Dobbins & Han, 2006 Hayama, Johnson, & Rugg, 2008), and provided strong evidence inconsistent with such an account. A serendipitous finding in this study was evidence for a left-frontal ERP old/new effect that was functionally and electrophysiologically dissociable from the right-frontal old/new effect, and which differentiated between high and low confidence correct source judgments. There was no evidence for this effect in Experiment Four, however, when auditory (male/female voice) rather than visual (pink/yellow letters) source information was to be retrieved at test, suggesting the content-specificity of this frontally distributed ERP effect. This possibility was tested directly in Experiment Five in which versions of Experiments Three and Four were completed within-participants. Two separable frontal old/new effects were observed. These effects differed in their scalp distributions as a function of the forms of episodic content that were retrieved (i.e. visual vs. auditory source). The scalp distributions of the frontal old/new effects across Experiments Three to Five also varied according to whether the data from the first or the second halves of retrieval phases were analysed. These qualitative changes in neural activity according to time on task are interpreted in terms of processes involved in the resolution of interference, which presumably increases during the course of a retrieval task. The implications of this finding for conclusions made on the basis of averaged measures of neural activity across the entirety of a retrieval task are also discussed. In combination, the data reported in this thesis provide evidence that ERPs are sensitive to multiple neurally, functionally, and temporally distinct PFC-supported processes which operate during episodic retrieval, and offer insights into the roles played by PFC during episodic retrieval.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available