Model Of Spoken Language Production Research Articles

A unified neurocomputational bilateral model of spoken language production in healthy participants and recovery in poststroke aphasia

Understanding the processes underlying normal, impaired, and recovered language performance has been a long-standing goal for cognitive and clinical neuroscience. Many verbally described hypotheses about language lateralization and recovery have been generated. However, they have not been considered within a single, unified, and implemented computational framework, and the literatures on healthy participants and patients are largely separated. These investigations also span different types of data, including behavioral results and functional MRI brain activations, which augment the challenge for any unified theory. Consequently, many key issues, apparent contradictions, and puzzles remain to be solved. We developed a neurocomputational, bilateral pathway model of spoken language production, designed to provide a unified framework to simulate different types of data from healthy participants and aphasic patients. The model encapsulates key computational principles (differential computational capacity, emergent division of labor across pathways, experience-dependent plasticity-related recovery) and provides an explanation for the bilateral yet asymmetric lateralization of language in healthy participants, chronic aphasia after left rather than right hemisphere lesions, and the basis of partial recovery in patients. The model provides a formal basis for understanding the relationship between behavioral performance and brain activation. The unified model is consistent with the degeneracy and variable neurodisplacement theories of language recovery, and adds computational insights to these hypotheses regarding the neural machinery underlying language processing and plasticity-related recovery following damage.

Idea Formulation for Spoken Language Production: The Interface of Cognition and Language.

Language and communication are fundamental to the human experience, and, traditionally, spoken language is studied as an isolated skill. However, before propositional language (i.e., spontaneous, voluntary, novel speech) can be produced, propositional content or 'ideas' must be formulated. This review highlights the role of broader cognitive processes, particularly 'executive attention', in the formulation of propositional content (i.e., 'ideas') for propositional language production. Several key lines of evidence converge to suggest that the formulation of ideas for propositional language production draws on executive attentional processes. Larger-scale clinical research has demonstrated a link between attentional processes and language, while detailed case studies of neurological patients have elucidated specific idea formulation mechanisms relating to the generation, selection and sequencing of ideas for expression. Furthermore, executive attentional processes have been implicated in the generation of ideas for propositional language production. Finally, neuroimaging studies suggest that a widely distributed network of brain regions, including parts of the prefrontal and parietal cortices, supports propositional language production. Theoretically driven experimental research studies investigating mechanisms involved in the formulation of ideas are lacking. We suggest that novel experimental approaches are needed to define the contribution of executive attentional processes to idea formulation, from which comprehensive models of spoken language production can be developed. Clinically, propositional language impairments should be considered in the context of broader executive attentional deficits.

Selection for sentence generation in the context of severe anomia: A case series of left temporal patients

ABSTRACTIntroduction: Anomia is an impairment of naming: the retrieval of specific lexical items from the mental lexicon. Theoretically, whether anomia reflects a failure of selection at the preverbal “idea” level or at the subsequent linguistic formulation stage remains a topic of debate. We investigated the preverbal mechanism of idea selection for sentence generation, which requires the selection of a proposition from among competing alternatives during message formulation, in patients with severe anomia.Method: Patients with lesions to the left temporal lobe (N = 12), presenting with clinically defined anomia, and matched healthy controls (N = 24) completed sentence-level tasks that required the oral generation of a sentence or single word when presented with a word, a word pair, or a sentence. Selection demands were manipulated so that the stimuli activated many competing response options (low constraint) or one dominant or few response options (high constraint).Results: There was no effect of stimuli constraint in the patient group that differed from that in the healthy control group on any of the generation tasks, suggesting that idea-level selection is intact in the patient group.Conclusions: These findings have implications for theoretical models of spoken language production and for clinical treatments of anomia.

Energization and spoken language production: Evidence from progressive supranuclear palsy

Energization is the process of initiating and sustaining a response over time. It has been described as one of three key “supervisory” attentional control processes associated with the frontal lobes. Attentional mechanisms, such as energization, are critical for a range of cognitive functions, such as spontaneous speech and other higher-order tasks. We aimed to investigate the process of energization in a case series of patients with progressive supranuclear palsy (PSP). Patients with a diagnosis of PSP (N = 5), patient controls with a neurodegenerative condition (Alzheimer's disease N = 3, frontotemporal dementia N = 2) and healthy older adult controls (N = 30) were assessed on a standard neuropsychological battery, including executive tasks and standard attention and language tests. Energization was investigated using word fluency tasks, samples of spontaneous speech and an experimental button-pressing concentration task. Response rates for the word fluency, spontaneous speech and concentration tasks were separated into time periods, in order to compare response rates at different points across the tasks (e.g., first 15 s vs. last 45 s in a 60 s task). Four PSP patients showed a clear response pattern indicative of a decrease in energization. Healthy and patient controls remained consistent in their responding over time. Understanding how these underlying processes are impaired in PSP can ultimately inform intervention and management strategies, and has theoretical implications for models of spoken language production.

"Twisting fingers": The case for interactivity in typed language production.

Despite the obvious linguistic nature of typing, current psychological models of typing are, to a large extent, divorced from models of spoken language production. This gap has left unanswered many questions regarding the cognitive architecture of typing. In this article we advocate the use of a psycholinguistic framework for studying typing, by showing that such a framework could reveal important similarities and differences between spoken and typed production. Specifically, we investigated the interaction between the lexical and postlexical layers by using a phenomenon known in spoken production as the "repeated-phoneme effect." Participants typed four-word sequences of "finger-twisters" (equivalent to tongue-twisters in spoken production), in which the vowel in the last two words was either repeated (e.g., "fog top") or not (e.g., "fog tip"). We found reliably more migration errors between the consonants of the two typed words when the vowel was repeated, even after the effect of phonology was accounted for. This finding is compatible with an interactive typing system in which postlexical representations send feedback to lexical representations and reveals similar dynamics between spoken and typed production. Additional analyses showed further similarities to spoken production, such as distinct lexical and postlexical error categories, but also revealed that typing errors were much more likely than spoken errors to violate phonotactic constraints. These results provide the first demonstration of feedback between the postlexical and lexical layers in typing, and more generally demonstrate the utility of adopting a psycholinguistic framework tailored specifically to the study of typing.

Apraxia of Speech: Concepts and Controversies

This article was written as an editorial to a collection of original articles on apraxia of speech (AOS) in which some of the more recent advancements in the understanding of this syndrome are discussed. It covers controversial issues concerning the theoretical foundations of AOS. Our approach was motivated by a change of perspective on motor speech that has taken place in neurobiology, neurolinguistics, phonology, and phonetics during the past few decades. The literature on AOS is reviewed from 3 different but overlapping perspectives-that is, a disconnection, a motor memory, and a fine motor skill perspective. Separate sections are devoted to the delimitations of AOS from oral facial apraxia, dysarthria, and phonological impairment. We conclude that many of the still unresolved conceptual issues about AOS arise from an underspecification of existing models of spoken language production. We suggest that phonological and motor impairments of sound production should be studied by an integrated approach.

Syllable- and Rhythm-Based Approaches in the Treatment of Apraxia of Speech

This paper presents new treatment approaches for patients with apraxia of speech (AOS), which are based on current theoretical work relating to the pathomechanism of AOS. Particularly, we focus on the question of which speech units and structural properties are involved in the error mechanism of speakers with apraxia. Based on a psycholinguistic model of spoken language production (Levelt, Roelofs, & Meyer, 1999), we review data from single-word production experiments and from analyses of spontaneous speech demonstrating an impact on (a) the degree of “over-learnedness” of syllables (syllable frequency), (b) the internal structure of syllables (syllable complexity), and (c) supra-syllabic, metrical aspects of utterances (word stress) on error production in AOS. In the second section, we present two experimental learning studies and a treatment study that take these results into consideration. The first learning experiment suggests that syllables are more natural units than segments in the treatment of patients with severe AOS. Based on the results of the second learning study, we recommend a treatment approach which uses formally related training syllables in the reacquisition of complex target syllables. Finally, results of a treatment study using a metrical pacing technique led to the assumption that fluency and segmental accuracy could be enhanced by external rhythmic cues.

Psycholinguistic and motor theories of apraxia of speech.

This article sketches the relationships between modern conceptions of apraxia of speech (AOS) and current models of neuromotor and neurolinguistic disorders. The first section is devoted to neurophysiological perspectives of AOS, and its relation to dysarthrias and to limb apraxia is discussed. The second section introduces the logogen model and considers AOS in relation to supramodal aspects of aphasia. In the third section, AOS with the background of psycholinguistic models of spoken language production, including the Levelt model and connectionist models, is discussed. In the fourth section, the view of AOS as a disorder of speech motor programming is discussed against the background of theories from experimental psychology. The final section considers two models of speech motor control and their relation to AOS. The article discusses the strengths and weaknesses of these approaches.