Traumatic brain injury (TBI) is frequently associated with both cognitive and behavioural executive dysfunction. Assessment of executive dysfunction has traditionally been measured using tests that were not based on theory and this has been postulated as one reason why there are poor predictive relationships between performance on traditional executive tasks and functional outcome following TBI. Baddeley�s (1996) working memory model may offer a theoretical basis with which to design new executive measures and possibly improve prediction of outcome. Baddeley�s theory has made recent advances in identifying core central executive (CE) processes that are likely to be relevant to TBI. The research presented in the thesis used Baddeley�s proposed coordinative sub function of the CE (and it related dual tasking measure) to assess: (a) whether this theoretically based dual tasking test would be sensitive to TBI injury status and show a significant relationship with functional outcome, (b) whether the theoretically based test would be more sensitive to the above relationships than executive measures that have been traditionally available, and (c) whether more ecologically relevant dual tasks could be developed that reflect the coordinative construct and improve predictive relationships between task performance and real life functional ability. This study found that Baddeley�s Dual Task Test (DTT) measure was sensitive to TBI injury and was related to functional outcome following injury. A questionnaire assessing everyday dual tasking ability was developed as was an in vivo conversation and motor based dual task. The dual tasking questionnaire reflected Baddeley�s coordinative construct, however, applications to an in vivo conversation and motor based dual task were less successful. These ecologically relevant tasks showed a relationship between language dysfluencies and dual tasking and identified avoidance of dual tasking in everyday settings as an important predictor of functional outcome following injury. Overall the DTT and the dual tasking questionnaire showed greater injury sensitivity and stronger relationships with outcome than three executive measures traditionally used in clinical practice. Regression analysis confirmed that the dual based tasks were helpful in predicting a variety of outcomes following TBI, and implications for rehabilitation planning are discussed. Further increases in the predictive power of the dual tasking construct are likely to be achieved when mechanisms of action involved in both laboratory-based and real-life dual tasking are identified. Findings from the current study suggest a range of mechanisms could be involved in dual tasks and these are discussed.

Although it is well established that persons with traumatic brain injury (TBI) experience word retrieval difficulties, the underlying cause of these deficits is not known. Difficulties with word retrieval have negative social implications as they can impact on the ability to converse with others. The overarching goal of this dissertation was to determine the underlying cause of problems with word retrieval after TBI. To test word retrieval in this dissertation, participants were given a series of word fluency tasks and the speed of word generation was measured. In addition to measuring interresponse times, procedures used by Rohrer, Wixted, Salmon and Butters (1995) were also followed. This involved the calculation of parameter estimates to investigate whether slowed retrieval or degraded semantic stores were responsible for the patients� word retrieval difficulties. One parameter (N) was a measure of the total number of retrievable words and the second parameter (tau) was an estimate of mean latency. Study 1 was designed to trial the procedure and equipment adopted throughout this dissertation to analyse speech. University students were presented with categories on a computer screen and asked to generate as many exemplars as possible in 60 seconds. A PowerLab Chart sound system was used to measure the time that each word was generated. The results of Study 1 showed that the methodology of previous research could be replicated using the PowerLab Chart sound system. In Study 2, persons with postconcussion syndrome (PCS) and matched controls were given two word fluency tasks. Results showed that on both tasks patients recalled fewer words, had longer pauses between words, and took significantly longer to generate their first word than controls. Also, patients had a significantly reduced N relative to controls, but there was no difference in tau between patients and controls. Given that the participants had not finished responding and that parameter estimates require responses to be exhausted, Study 3 was designed to replicate the findings of Study 2 using an extended recall period. In Study 3, patients with PCS and matched controls completed a series of word fluency tasks and were given extended periods of time to generate words. Results showed that the patients obtained significantly fewer words on two of the tasks, but no evidence of slowed retrieval was found. There was also no difference in the estimates of N and tau between patients and controls. As the patients in Study 3 sustained more minor injuries than those in Study 2, Study 4 tested patients with severe TBI. In Study 4, patients with severe TBI and matched controls were given a series of word fluency tasks. Results showed that the patients generated fewer words and experienced slowed retrieval. Again, there was no difference in the estimates of N and tau between patients and controls. The results of Study 4 confirmed the hypothesis that slowed word retrieval is a consequence of TBI. Taken together, the results of this dissertation show that an underlying slowness of processing is the primary cause of problems with word retrieval in persons with TBI.

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 148-172). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19801

Thesis (Ph.D.)--University of Adelaide, Dept. of Pathology, 2004? / Includes list of articles published or accepted for publication during the period of PhD candidature. "July, 2004" Includes bibliographical references (leaves 255-293).

Thesis (MHSc--Health Science) -- Auckland University of Technology, 2003. / Also held in print (251 leaves, 30 cm.) in North Shore Theses Collection (T 617.4810443083 JON).

Thesis (M. Phil.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 90-101).

Thesis (Ph. D.)--University of North Texas, August, 2008. / Title from title page display. Includes bibliographical references.

Thesis (M.A.)--Miami University, Dept. of Speech Pathology and Audiology, 2004. / Title from first page of PDF document. Includes bibliographical references (p. 54-59).

Thesis (Ph.D.)--York University, 2005. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 102-140). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNR11564

Thesis (doctoral)--La Salle University, 2005. / ProQuest dissertations and theses ; AAT 3227733. Includes bibliographical references (leaves 49-65)