The aim of this study was to investigate two factors that have been claimed to be associated with the word retrieval difficulties experienced by individuals with aphasia. These factors were aphasic subjects’ level of phonological awareness and their lexical semantic processing. (For complete abstract open document)

Verbal communication relies heavily on the ability to effortlessly produce intended words to express a meaning. This capacity is frequently impaired in individuals with aphasia, and impairment often lasts well into the chronic stages. However, the nature of anomia can vary. Phonological neighborhood density (PND) is one feature of words which has been shown to impact the ease of retrieval in speakers with aphasia; words with more similar-sounding neighbors are easier to retrieve because the neighbors help activate the target. However, it is unclear how different types of lexical access breakdowns affect the impact of PND. The aim of this project was to analyze the relationship between word retrieval accuracy, speech error patterns, and PND in individuals with aphasia. Twenty-two participants with various types and severities of aphasia named 200 single-syllable line drawings. WebFit, an online software program designed to fit naming data to a theoretical model of word retrieval, was used to characterize participants' error patterns by calculating the strength of connections within the lexicon, as well as the rate of decay. Analyses confirmed previous findings that participants with all types of breakdown achieved lower rates of overall accuracy. Weaker connections between semantic knowledge and words resulted in a more errors that were close to the target, relative to errors with no relationship to the target. Individuals with more severe impairments of the semantic-lexical connections and the lexical-phonological connections produced words with many neighbors more accurately than words with fewer neighbors. Implications for initial therapy target selection and directions for further research 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.

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.

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The aims of this study were to determine if various treatment, item, and patient-level factors could be used to predict probe naming accuracy in a bilingual Spanish-English SFA treatment study. At the treatment-level, variables included phase (baseline vs. treatment), training condition (trained set 1 items vs. translations), and time (session). At the item-level, psycholinguistic variables were investigated including lexical frequency, phonological length in phones, and phonological neighborhood density. Finally, at the patient-level, impairment measures were used including aphasia severity (as measured by WAB AQ) naming impairment (represented by a composite naming score from pre-treatment assessments). Mixed-effects logistic regression methods were used to fit the data with fixed effects for the variables of interest as well as random effects for subject and item. The regression analyses revealed significant main effects of phase, time, and interactions with training condition such that naming accuracy on probes was higher for the treatment language during the treatment phase and over time in general. Significant effects were also noted for each of the psycholinguistic variables such that increased frequency, shorter length, and a larger neighborhood increased the likelihood of correct naming responses. Finally, overall aphasia severity and naming impairment both correlated with naming outcomes.

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Including response delays in language tasks yields variable results for people with aphasia. Some improve relative to immediate response conditions, others perform more poorly, and others show no significant change. The effect of response delays on performance accuracy varies within individuals depending on the language task. The mechanism that drives this heterogeneity is unknown. In these studies, we investigated factors contributing to differences in performance accuracy in naming and repetition following a response delay. In Experiment 1, we explored the contribution of stimulus duration to accuracy in delay conditions by manipulating picture exposure time in naming. We hypothesized that shorter picture exposure times would lead to lower accuracy in delayed naming conditions, similar to an established trend in delayed repetition (Sayers et al. 2023c). Shorter picture exposure time was associated with lower accuracy and greater variety of temporal impairments (i.e., improved or poorer performance) than naming with longer exposure times. Shortening picture exposure time may reduce contributions of visual semantics, increasing reliance on the language system. In Experiment 2, we compared the measures of the timeliness of semantic and phonological activation transmission with performance in immediate and delayed naming and repetition. Slower semantic activation transmission was associated with relatively improved performance in delayed naming but poorer performance in delayed repetition. We attribute this to the order of access to linguistic representations. In naming, semantic activation initiates the retrieval process, while in repetition, it supports phonological activation, making it more enduring in the face of decay in delayed response conditions. / Communication Sciences

The purpose of this study was to examine the extent to which learning and recall are facilitated by semantic and phonological targets. A list-learning paradigm was administered to 10 individuals with a history of traumatic brain injury. Participants were asked to recall and identify words that were present on the list. The lists consisted of semantically related associate words and phonologically related associate words. Participants recalled significantly more semantically related associates than phonological associates. Demographic factors such as age, time-post injury, and educational attainment did not have a significant effect on the recall ability for either word target type. Word recognition ability also was not influenced by target type. The results of this study found adults with TBI use a semantic network following brain injury and that semantic targets are more beneficial for recall than phonological targets. / text