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Speech-like cerebral activity in profoundly deaf people processing signed languages: implications for the neural basis of human language.

ABSTRACT: For more than a century we have understood that our brain's left hemisphere is the primary site for processing language, yet why this is so has remained more elusive. Using positron emission tomography, we report cerebral blood flow activity in profoundly deaf signers processing specific aspects of sign language in key brain sites widely assumed to be unimodal speech or sound processing areas: the left inferior frontal cortex when signers produced meaningful signs, and the planum temporale bilaterally when they viewed signs or meaningless parts of signs (sign-phonetic and syllabic units). Contrary to prevailing wisdom, the planum temporale may not be exclusively dedicated to processing speech sounds, but may be specialized for processing more abstract properties essential to language that can engage multiple modalities. We hypothesize that the neural tissue involved in language processing may not be prespecified exclusively by sensory modality (such as sound) but may entail polymodal neural tissue that has evolved unique sensitivity to aspects of the patterning of natural language. Such neural specialization for aspects of language patterning appears to be neurally unmodifiable in so far as languages with radically different sensory modalities such as speech and sign are processed at similar brain sites, while, at the same time, the neural pathways for expressing and perceiving natural language appear to be neurally highly modifiable.

SUBMITTER: Petitto LA

PROVIDER: S-EPMC17683 | biostudies-literature | 2000 Dec

REPOSITORIES: biostudies-literature

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Speech-like cerebral activity in profoundly deaf people processing signed languages: implications for the neural basis of human language.

Petitto L A LA Zatorre R J RJ Gauna K K Nikelski E J EJ Dostie D D Evans A C AC

Proceedings of the National Academy of Sciences of the United States of America 20001201 25

For more than a century we have understood that our brain's left hemisphere is the primary site for processing language, yet why this is so has remained more elusive. Using positron emission tomography, we report cerebral blood flow activity in profoundly deaf signers processing specific aspects of sign language in key brain sites widely assumed to be unimodal speech or sound processing areas: the left inferior frontal cortex when signers produced meaningful signs, and the planum temporale bilat ...[more]

PMID: 11106400

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Project description:BackgroundPrevious research has been designed to study the effect of hearing loss on supra-second duration estimation in the visual channel and position effect of visual abilities among deaf populations. The current study aimed to investigate the sub-second duration perception of different visual fields in profoundly deaf individuals.MethodsA total of 16 profoundly deaf undergraduates and 16 hearing undergraduates completed a visual duration bisection task in which participants made judgments about whether a series of probe durations that were linearly spaced from 200 ms to 800 ms at 100 ms intervals were more similar to a standard short duration (200 ms) or a standard long duration (800 ms). The probe stimuli were presented in the center, left, or right of the screen. A repeated measure analysis of variance (ANOVA) with a between-participants factor of group and a within-participants factor of position, and a one-sample t-test were conducted.ResultsThe Weber ratio (WR) values of deaf participants were significantly higher than those of hearing participants, regardless of the presented positions of the visual stimulus. The bisection point (BP) value of deaf participants was significantly lower than 500 ms (average mean of 200/800 ms) and the BP value of hearing participants did not significantly differ from 500 ms, although the overall difference of BP values between the deaf group and hearing group did not reach significance. For deaf participants, the BP value in the center condition was significantly lower than 500 ms; however, the difference between the BP value in the left condition and 500 ms did not reach significance, indicating that their duration discrimination accuracy in the left visual field was better than that in the center visual field.ConclusionsHearing loss impaired visual sub-second duration perception, and deaf individuals showed a left visual field advantage of duration discrimination accuracy during the visual duration bisection task.

Project description:We present here the first neuroimaging data for perception of Cued Speech (CS) by deaf adults who are native users of CS. CS is a visual mode of communicating a spoken language through a set of manual cues which accompany lipreading and disambiguate it. With CS, sublexical units of the oral language are conveyed clearly and completely through the visual modality without requiring hearing. The comparison of neural processing of CS in deaf individuals with processing of audiovisual (AV) speech in normally hearing individuals represents a unique opportunity to explore the similarities and differences in neural processing of an oral language delivered in a visuo-manual vs. an AV modality. The study included deaf adult participants who were early CS users and native hearing users of French who process speech audiovisually. Words were presented in an event-related fMRI design. Three conditions were presented to each group of participants. The deaf participants saw CS words (manual + lipread), words presented as manual cues alone, and words presented to be lipread without manual cues. The hearing group saw AV spoken words, audio-alone and lipread-alone. Three findings are highlighted. First, the middle and superior temporal gyrus (excluding Heschl's gyrus) and left inferior frontal gyrus pars triangularis constituted a common, amodal neural basis for AV and CS perception. Second, integration was inferred in posterior parts of superior temporal sulcus for audio and lipread information in AV speech, but in the occipito-temporal junction, including MT/V5, for the manual cues and lipreading in CS. Third, the perception of manual cues showed a much greater overlap with the regions activated by CS (manual + lipreading) than lipreading alone did. This supports the notion that manual cues play a larger role than lipreading for CS processing. The present study contributes to a better understanding of the role of manual cues as support of visual speech perception in the framework of the multimodal nature of human communication.

Project description:BackgroundLanguage impairment is an important marker of neurodegenerative disorders. Despite this, there is no universal system of terminology used to describe these impairments and large inter-rater variability can exist between clinicians assessing language. The use of natural language processing (NLP) and automated speech analysis (ASA) is emerging as a novel and potentially more objective method to assess language in individuals with mild cognitive impairment (MCI) and Alzheimer's dementia (AD). No studies have analyzed how variables extracted through NLP and ASA might also be correlated to language impairments identified by a clinician.MethodsAudio recordings (n=30) from participants with AD, MCI, and controls were rated by clinicians for word-finding difficulty, incoherence, perseveration, and errors in speech. Speech recordings were also transcribed, and linguistic and acoustic variables were extracted through NLP and ASA. Correlations between clinician-rated speech characteristics and the variables were compared using Spearman's correlation. Exploratory factor analysis was applied to find common factors between variables for each speech characteristic.ResultsClinician agreement was high in three of the four speech characteristics: word-finding difficulty (ICC = 0.92, p<0.001), incoherence (ICC = 0.91, p<0.001), and perseveration (ICC = 0.88, p<0.001). Word-finding difficulty and incoherence were useful constructs at distinguishing MCI and AD from controls, while perseveration and speech errors were less relevant. Word-finding difficulty as a construct was explained by three factors, including number and duration of pauses, word duration, and syntactic complexity. Incoherence was explained by two factors, including increased average word duration, use of past tense, and changes in age of acquisition, and more negative valence.ConclusionsVariables extracted through automated acoustic and linguistic analysis of MCI and AD speech were significantly correlated with clinician ratings of speech and language characteristics. Our results suggest that correlating NLP and ASA with clinician observations is an objective and novel approach to measuring speech and language changes in neurodegenerative disorders.

Dataset Information

Speech-like cerebral activity in profoundly deaf people processing signed languages: implications for the neural basis of human language.

Publications

Speech-like cerebral activity in profoundly deaf people processing signed languages: implications for the neural basis of human language.

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