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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- "This area is thought to underpin a sensorimotor interface between auditory representations in STG and articulation-related representations in the precentral gyrus and posterior inferior frontal gyrus (for an integration of this hypothesis into WEAVERþþ, see Roelofs, 2014a). Damage confined to the connections between lexical output forms and output phonemes in the model (thought to correspond to the lexical-semantic part of the AF) led to impaired production with spared repetition and comprehension (Fig. 2D), as typically observed in transcortical motor aphasia (Damasio & Geschwind, 1984; Freedman et al., 1984; Geschwind, 1970, 1972; Glasser & Rilling, 2008; McCarthy & Warrington, 1984). Transcortical motor aphasia is classically associated with frontal lesions sparing Broca's area, in the region of the termination of the lexical-semantic AF pathway (resulting from a vascular accident involving the left anterior cerebral artery or the " watershed " areas between the anterior cerebral artery and the superior division of the MCA, see Hillis, 2007). "
ABSTRACT: It has long been assumed that a dorsal pathway running from temporal to inferior frontal cortex underpinned by the left arcuate fasciculus (AF) underlies both repetition and spoken language production. However, according to a recent proposal, a ventral pathway underpinned by extreme capsule (EmC) and uncinate fasciculus (UF) fiber tracts is primarily responsible for language production, whereas the AF primarily underlies repetition. Here, a computational implementation of the dorsal-pathway account of language production is presented, called WEAVER++/ARC (for WEAVER++ Arcuate Repetition and Conversation), which synthesizes behavioral psycholinguistic, functional neuroimaging, and tractographic evidence. The results of computer simulations revealed that the model accounts for the typical patterns of impaired and spared language performance associated with classic acute-onset and progressive aphasias. Moreover, the model accounts for recent evidence that damage to the AF but not the EmC/UF pathway predicts impaired production performance. It is concluded that the results demonstrate the viability of a dorsal-pathway account of language production.Cortex 10/2014; 59. DOI:10.1016/j.cortex.2014.07.001 · 6.04 Impact Factor
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- "The key features of this pattern have been explained in alternative frameworks in which the phonemic errors are more typically attributed to a deficit in speech planning related to reduction in some type of phonological buffering or working memory capacity (Goodglass, 1992; see also Baldo, Klosterman, & Dronkers , 2008) or instability of phonemic representations. Also seemingly problematic are the reports of individuals with good speech perception and comprehension and good repetition but who nonetheless produce primarily phonemic errors in naming and spontaneous speech (e.g., Goldrick & Rapp, 2007; Kay & Ellis, 1987; Law, 2004; McCarthy & Warrington, 1984). Their good comprehension indicates that the link between word meaning and auditory form is intact. "
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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- "Analysis of repetition performance in the other two patients yielded mixed results. Evaluation in patient JNR replicated the results obtained in EDE (except for abnormal phonological input processing), but patient ORL had repetition deficits similar to the ones described in cases with CA and left hemisphere involvement (see further details in Berthier et al., 2011; McCarthy and Warrington, 1984). In light of the limited data available and mixed results on the pattern of repetition in patients with crossed CA, analysis of further cases is clearly needed. "
ABSTRACT: Knowledge on the patterns of repetition amongst individuals who develop language deficits in association with right hemisphere lesions (crossed aphasia) is very limited. Available data indicate that repetition in some crossed aphasics experiencing phonological processing deficits is not heavily influenced by lexical-semantic variables (lexicality, imageability, and frequency) as is regularly reported in phonologically-impaired cases with left hemisphere damage. Moreover, in view of the fact that crossed aphasia is rare, information on the role of right cortical areas and white matter tracts underpinning language repetition deficits is scarce. In this study, repetition performance was assessed in two patients with crossed conduction aphasia and striatal/capsular vascular lesions encompassing the right arcuate fasciculus (AF) and inferior frontal-occipital fasciculus (IFOF), the temporal stem and the white matter underneath the supramarginal gyrus. Both patients showed lexicality effects repeating better words than non-words, but manipulation of other lexical-semantic variables exerted less influence on repetition performance. Imageability and frequency effects, production of meaning-based paraphrases during sentence repetition, or better performance on repeating novel sentences than overlearned clichés were hardly ever observed in these two patients. In one patient, diffusion tensor imaging disclosed damage to the right long direct segment of the AF and IFOF with relative sparing of the anterior indirect and posterior segments of the AF, together with fully developed left perisylvian white matter pathways. These findings suggest that striatal/capsular lesions extending into the right AF and IFOF in some individuals with right hemisphere language dominance are associated with atypical repetition patterns which might reflect reduced interactions between phonological and lexical-semantic processes.Frontiers in Human Neuroscience 10/2013; 7:675. DOI:10.3389/fnhum.2013.00675 · 2.90 Impact Factor