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.
| Identifer | oai:union.ndltd.org:ADTP/217384 |
| Date | January 2005 |
| Creators | Crawford, Maria Anne, n/a |
| Publisher | University of Otago. Department of Psychology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Maria Anne Crawford |
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