A two-route model of speech production. Evidence from aphasia.
ABSTRACT Quantitative investigations of speech production deficits are reported in three aphasic patients. Two had impaired paraphasic performance in repetition tasks but relatively well preserved spontaneous speech (conduction aphasia). The other patient had impaired paraphasic spontaneous speech but intact repetition (transcortical motor aphasia). In repetition tasks which required active semantic processing the conduction aphasics were facilitated and the transcortical motor aphasic impaired; in tasks which required passive repetition the opposite pattern of dissociation was observed. These findings are accounted for within a two-route model of the speech production process.
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ABSTRACT: This commentary focuses on two key aspects of Hickok's proposal that distinguish it from other theories of speech production. Unlike many other accounts, auditory targets play a central and early role in speech production. This proposal also adopts a generally reductionist approach to the production of speech, relying almost exclusively on sensory and motor processes to represent sound structure. This eliminates various levels of phonological representation that play key roles in theories motivated by psycholinguistic and cognitive neuropsychological research. The general and specific issues raised by Hickok's approach are examined within two specific areas: the structure of sound representations and patterns of performance in "conduction aphasia."Language, Cognition and Neuroscience 01/2014; 29(1):24. DOI:10.1080/01690965.2013.848991 · 1.93 Impact Factor
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ABSTRACT: Background: We recently constructed a single-word speech intelligibility test intended to quantify magnitude of speech sound impairment in individuals with aphasia. To minimise listener learning and strategising, the test included a large set of possible (alternate) test forms and was constructed with high and diverse phonologic similarity among candidate words. Although the corpus was limited in phonetic complexity to single syllables, and although criteria for minimal word frequency were applied, it is possible that more fine-grained differences in phonetic complexity and/or word frequency may introduce varying levels of difficulty across alternate test forms and that reliability, therefore, may be compromised.Aims: The dual purposes of this study were to evaluate alternate forms reliability for the new intelligibility test and to determine whether word frequency and/or phonetic complexity affected word identification scores.Methods & Procedures: All words in the 600-word test corpus were coded for overall phonetic complexity and for frequency of occurrence in spoken English. Fifty-one versions of the target 50-word test were generated from this corpus by following designated pseudo-random selection procedures. Speech samples were collected from 13 speakers with aphasia, who each repeated three or four of these 50-word sets. Ten normal-hearing listeners were asked to indicate the words they thought the speakers were trying to say. Per cent accuracy was computed for each speaker, test form and target word.Outcomes & Results: The intra-class correlation within speakers was 0.97, indicating that the scores across alternate forms were highly reproducible. Analyses at the word level showed that both phonetic complexity and word frequency affected identification accuracy. The effects were seen in almost all participants whose intelligibility scores were in the impaired range.Conclusions: High frequency of occurrence and low phonetic complexity increase repetition accuracy for individuals with moderate to severe sound production difficulties and aphasia. However, the pseudo-random word selection in the examined word intelligibility test was sufficient to ensure strong alternate forms reliability. Further constraints on the word selection process for this test are not warranted.Aphasiology 11/2013; 28(3):320-337. DOI:10.1080/02687038.2013.855702 · 1.73 Impact Factor