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Biomedical subjects

J Gandour

Publications and source records attributed to J Gandour.

At least 19 recordsLinked to original sources
PubMed2001

Functional heterogeneity of inferior frontal gyrus is shaped by linguistic experience.

A crosslinguistic, positron emission tomography (PET) study was conducted to determine the influence of linguistic experience on the perception of segmental (consonants and vowels) and suprasegmental (tones) information. Chinese and English subjects (10 per group) were presented binaurally with lists consisting of five Chinese monosyllabic morphemes (speech) or low-pass-filtered versions of the same stimuli (nonspeech). The first and last items were targeted for comparison; the time interval between target tones was filled with irrelevant distractor tones. A speeded-response, selective attention paradigm required subjects to make discrimination judgments of the target items while ignoring intervening distractor tones. PET scans were acquired for five tasks presented twice: one passive listening to pitch (nonspeech) and four active (speech = consonant, vowel, and tone; nonspeech = pitch). Significant regional changes in blood flow were identified from comparisons of group-averaged images of active tasks relative to passive listening. Chinese subjects show increased activity in left premotor cortex, pars opercularis, and pars triangularis across the four tasks. English subjects, on the other hand, show increased activity in left inferior frontal gyrus regions only in the vowel task and in right inferior frontal gyrus regions in the pitch task. Findings suggest that functional circuits engaged in speech perception depend on linguistic experience. All linguistic information signaled by prosodic cues engages left-hemisphere mechanisms. Storage and executive processes of working memory that are implicated in phonological processing are mediated in discrete regions of the left frontal lobe.

Adult↗
PubMed2001

Production of stress retraction by left- and right-hemisphere-damaged patients.

An acoustic-perceptual investigation of a phonological phenomenon in which stress is retracted in double-stressed words (e.g., thirTEEN vs THIRteen MEN) was undertaken to identify the locus of functional impairments in speech prosody. Subjects included left-hemisphere-damaged (LHD) and right-hemisphere-damaged (RHD) patients and nonneurological controls. They were instructed to read sentences containing double-stressed target words in the presence of a clause boundary or its absence. Whereas all three groups of subjects were capable of manipulating the acoustic parameters that signal a shift in stress, there were some differences between the performance of the patient groups and that of the normal controls. Further, stress production deficits were more severe in LHD aphasic patients than in RHD patients. LHD speakers exhibited deficits in the control of both temporal and F0 cues. Their F0 disturbance appears to be secondary to a primary deficit in temporal control at the phase or sentence level, as an increased number of continuation rises found for the LHD patients seemed to arise from lengthy pauses within sentences. Findings are highlighted to address the nature of breakdown in speech prosody and the competing views of prosodic lateralization.

Adolescent↗
PubMed2000

Speech timing in Thai left- and right-hemisphere-damaged individuals.

An acoustic analysis of syllable duration in short Thai phrases was conducted to evaluate the effects of focal brain damage on the control of speech timing. Almost all 35 of the subjects had participated in each of four previous companion studies: 13 left-brain-damaged (6 nonfluent aphasics; 7 fluent aphasics), 14 right-brain-damaged patients, and 8 normal controls. Somewhat surprisingly, results revealed relatively normal timing patterns in 3-syllable phrases in all subject groups. A comparison of the current study and the four others, however, led us to conclude that Thai-speaking nonfluent aphasics exhibit a speech timing deficit regardless of the linguistic level of representation, whereas timing deficits in fluent aphasics appear to be restricted to units larger than a syllable. Speech timing, on the other hand, appears to be intact across the board in right-brain-damaged individuals. Findings are brought to bear on theories of temporal control in brain-damaged patients.

Acoustics↗
PubMed2000

A crosslinguistic PET study of tone perception.

In studies of pitch processing, a fundamental question is whether shared neural mechanisms at higher cortical levels are engaged for pitch perception of linguistic and nonlinguistic auditory stimuli. Positron emission tomography (PET) was used in a crosslinguistic study to compare pitch processing in native speakers of two tone languages (that is, languages in which variations in pitch patterns are used to distinguish lexical meaning), Chinese and Thai, with those of English, a nontone language. Five subjects from each language group were scanned under three active tasks (tone, pitch, and consonant) that required focused-attention, speeded-response, auditory discrimination judgments, and one passive baseline as silence. Subjects were instructed to judge pitch patterns of Thai lexical tones in the tone condition; pitch patterns of nonspeech stimuli in the pitch condition; syllable-initial consonants in the consonant condition. Analysis was carried out by paired-image subtraction. When comparing the tone to the pitch task, only the Thai group showed significant activation in the left frontal operculum. Activation of the left frontal operculum in the Thai group suggests that phonological processing of suprasegmental as well as segmental units occurs in the vicinity of Broca's area. Baseline subtractions showed significant activation in the anterior insular region for the English and Chinese groups, but not Thai, providing further support for the existence of possibly two parallel, separate pathways projecting from the temporo-parietal to the frontal language area. More generally, these differential patterns of brain activation across language groups and tasks support the view that pitch patterns are processed at higher cortical levels in a top-down manner according to their linguistic function in a particular language.

Adult↗
PubMed2000

The phonological similarity effect in immediate recall: positions of shared phonemes.

Earlier literature proposes two ways phonological similarity could harm immediate recall: (1) It could increase the degradation of the representations of items in memory, or (2) it could decrease the probability that a degraded representation is correctly reconstructed. A multinomial processing tree model for each hypothesis was used to analyze an immediate recall experiment. Both gave a good account of the data, but, of the two, results favor the hypothesis that the effect of phonological similarity is to impair reconstruction of degraded representations. A second issue is whether positions of repeated phonemes in phonologically similar items matter. We found that mere repetition of phonemes produced a phonological similarity effect. Repeated phonemes in the same positions appeared to produce a greater effect. A final finding is that when reading rate was preequated, phonological similarity affected memory span by changing the time taken to recall a list of span length.

Attention↗
PubMed1999

Effect of sentence length on the production of linguistic stress by left- and right-hemisphere-damaged patients.

An acoustical/perceptual study of phonemic stress (e.g., HOTdog vs. hot DOG) was conducted to evaluate the effect of sentence length on stress production after brain damage. Productions of phonemic stress pairs were elicited in sentence contexts of increasing length from eight left-hemisphere-damaged nonfluent (LHD-NFL), fluent LHD-FL), right-hemisphere-damaged (RHD), and normal speakers (n = 32). Tape recordings of subjects' productions were presented to naïve listeners for perceptual identification of stress placement. Acoustic analysis focused on fundamental frequency, duration, and intensity of the initial and final syllables as well as pause duration between syllables. Perceptual tests indicated that regardless of sentence length, all brain-damaged groups exhibited an impairment in the production of linguistic stress when compared to normals. The LHD-NFL group experienced the greatest difficulty in signaling stress contrasts, followed in order by the LHD-FL and RHD groups. In medium-length sentences, the LHD-FL group's performance was degraded by comparison to short-length sentences. Acoustic analysis showed that pause duration was the strongest predictor of phonemic stress for all groups. Acoustic profiles of the RHD group were similar qualitatively to those of normals, but differed quantitatively in terms of magnitude of effect associated with shifts in stress patterns. Findings are brought to bear on the nature of the stress production deficit after unilateral brain damage, the role of the right hemisphere in linguistic prosody, and the concept of "subtle phonetic deficit" in fluent aphasia.

Acoustics↗
PubMed1998

Locus of functional impairment in the production of speech rhythm after brain damage: a preliminary study.

This acoustic-perceptual, multiple-case study of the Rhythm Rule (RR) in English, a phonological phenomenon whereby adjacent stresses are adjusted to avoid "stress clash" (e.g., thirTEEN vs THIRteen MEN), was undertaken to identify the locus of functional impairments in speech prosody in different aphasic syndromes. Subjects included two left brain-damaged aphasic patients (1 fluent, 1 nonfluent), one right brain-damaged nonaphasic patient, and one nonneurological control. They were instructed to read sentences including experimental (bisyllabic "double-stressed" words) and matching control (bisyllabic "initial-stressed" words) phrases of increasing length. Results of acoustic and perceptual measures indicated that rhythmic disturbances associated with the RR emerged regardless of lesion site. The locus of functional impairment was isolated to phonetic implementation of the RR, as opposed to either loss of word-level stress or loss of the RR. Findings suggest that neural substrates of speech prosody are broadly distributed in the left and right cerebral hemispheres.

Brain Injuries↗
PubMed1998

Pitch processing in the human brain is influenced by language experience.

Positron emission tomography (PET) was used in a cross-linguistic study to compare pitch processing in native speakers of English, a nontone language, with those of Thai, a tone language. When discriminating pitch patterns in Thai words, only the Thai subjects showed activation in the left frontal operculum. Activation of this region near the classically defined Broca's area suggests that the brain recognizes functional properties, rather than simply acoustic properties, of complex auditory cues in accessing language-specific mechanisms in pitch perception.

Acoustic Stimulation↗
PubMed1997

Interaction between tone and intonation in Thai after unilateral brain damage.

Intonational characteristics of Thai sentences were used to evaluate fundamental frequency (F(0)) control in brain-damaged patients with unilateral left and right hemisphere lesions. Subjects (n = 41) included 9 young and 10 old normal adults, 12 right hemisphere patients, and 10 left hemisphere aphasic patients (7 fluent and 3 nonfluent). Sentences were comprised of six words, three of which were keywords occurring in sentence-initial, -medial, and -final positions. All 125 possible sequences of three of the five Thai tones (mid, low, falling, high, rising) were superimposed on monosyllabic keywords. Utterances were produced at a conversational speaking rate. Average F(0) of keywords was analyzed as a function of sentence position, tone, and group. For both normal and brain-damaged speakers, results indicated that tones in sentence-final position were significantly lower in F(0) than in either sentence-initial or -medial position; falling and high tones were significantly higher in F(0) than mid, low, and rising tones. Findings are discussed in relation to issues pertaining to hemispheric specialization and the nature of F(0) deficits in nonfluent and fluent aphasic patients.

Adult↗
PubMed1997

Contextual variations in trisyllabic sequences of Thai tones.

It is well known that tones assimilate in much the same way as consonants and vowels do. In tonal assimilation, the height and shape of a given tone is altered by adjacent tones. Earlier studies on tonal assimilation in Thai have used two-tone sequences with an intervening obstruent between the two tones of interest. In the present study, three-tone sequences were used with continuously voiced syllables throughout the utterance. Assimilatory effects were expected to be greater between F0 contours of two successive syllables that are continuous in voicing across the syllable boundary. Stimuli consisted of 125 possible three-tone sequences of the five Thai tones, superimposed on monosyllabic words in a carrier sentence. All syllables were stressed in order to eliminate potentially confounding interactions between stress and tonal assimilation. Acoustic analysis revealed that perseverative effects were assimilatory in nature; anticipatory effects, however, were dissimilatory in nature. Perseverative effects appear to be independent of tonal categories, and restricted to contiguous tones. Perseverative effects extend through more than half the duration of the following tone. Both the height and shape of the tones are affected. Anticipatory effects, on the other hand, are limited to the high and rising tones, and extend through less than half the duration of the preceding tone.

Adult↗
PubMed1996

Tonal coarticulation in Thai after unilateral brain damage.

The magnitude and temporal extent of anticipatory and perseverative tonal coarticulation was investigated in Thai-speaking normal and brain-damaged adults. A total of 47 speakers (10 young normal, 10 old normal, 13 nonaphasic right-brain-damaged patients, 14 left-brain-damaged aphasic patients, 9 fluent, 5 nonfluent) produced all 25 possible sequences of two tones from the five lexical tones of Thai embedded in a carrier sentence. F0 contours were analyzed in terms of height and slope at 10% intervals throughout the duration of the two syllables. Acoustic analysis revealed that anticipatory and perseverative tonal coarticulation of tones was markedly reduced in left fluent aphasics, totally absent in left nonfluent aphasics, but reasonably intact in right hemisphere patients. Findings are interpreted to highlight the nature of speech disturbances in nonfluent and fluent aphasia, hemispheric specialization for tone, and tonal coarticulation in Thai.

Adult↗
PubMed1996

Acoustic correlates of stress in Thai.

Acoustic correlates of stress [duration, fundamental frequency (Fo), and intensity] were investigated in a language (Thai) in which both duration and Fo are employed to signal lexical contrasts. Stimuli consisted of 25 pairs of segmentally/tonally identical, syntactically ambiguous sentences. The first member of each sentence pair contained a two-syllable noun-verb sequence exhibiting a strong-strong (--) stress pattern, the second member a two-syllable noun compound exhibiting a weak-strong (--) stress pattern. Measures were taken of five prosodic dimensions of the rhyme portion of the target syllable: duration, average Fo, Fo standard deviation, average intensity, and intensity standard deviation. Results of linear regression indicated that duration is the predominant cue in signaling the distinction between stressed and unstressed syllables in Thai. Discriminant analysis showed a stress classification accuracy rate of over 99%. Findings are discussed in relation to the varying roles that Fo, intensity, and duration have in different languages given their phonological structure.

Adult↗
PubMed1995

On the notion of a "subtle phonetic deficit" in fluent/posterior aphasia.

Phonetic investigations in the past decade or so have reported instances of a "subtle phonetic deficit" in the fluent aphasias, thereby challenging the traditional dichotomy of a motoric deficit characterizing the nonfluent aphasias and a selection deficit characterizing the fluent aphasias. This paper critically reviews the acoustic, physiological, and perceptual studies which have attempted to examine this phenomenon. These investigations have been evaluated in terms of differences in subject populations, task demands, subjects' performance, and problematic interpretations. Suggestions are offered for an experimental design which can help us operationalize this term and help us to better understand the speech production deficit in fluent aphasic patients.

Aphasia, Wernicke↗
PubMed1995

Speech prosody in affective contexts in Thai patients with right hemisphere lesions.

The production of speech prosody in emotional contexts was examined in Thai patients with unilateral right hemisphere damage. Twelve right hemisphere patients and nine normals read target sentences embedded in paragraphs that cued either a happy, sad, or neutral affect. Perceptual evaluations of their productions revealed a severe deficit in right hemisphere patients. Acoustic analysis indicated that longterm measures of fundamental frequency, timing, and energy at the sentence level were aberrant in right hemisphere patients. Findings are discussed in relation to nature and extent of prosodic deficits in right hemisphere patients, hemispheric specialization for linguistic and affective prosody, and the effect of language structure on the manifestation of affective prosody.

Adult↗
PubMed1994

Sequences of phonemic approximations in a Thai conduction aphasic.

Sequences of phonemic approximations (SPAs) to a single target word on a picture naming task were investigated in a Thai-speaking conduction aphasic. A corpus of 207 SPAs was analyzed with an adaptation of Valdois, Joanette, and Nespoulous's (1989) methodology to a tone language. Measures included the length of SPAs, overall degree of approximation to the target of the last attempt and each of the preceding attempts, as well as degree of approximation to the target in terms of number of syllables, syllable structure, segments (consonants/vowels), and tones. Results indicated that there was a steady progression toward the target regardless of eventual outcome or length of sequence. Number of syllables of the target word was better preserved than syllable structure, and tones better than segments. In the course of SPAs, tonal information was accessed earlier than segmental, and syllabic length information earlier than syllabic structure. Within SPAs, tonal information was more stable than segmental across successive approximations. Findings are discussed in relation to a functional model of single word production and multidimensional phonological representations.

Aphasia↗
PubMed1994

Speech timing at the sentence level in Thai after unilateral brain damage.

The present study examined temporal characteristics of spoken sentences in Thai to evaluate timing control in brain-damaged patients with unilateral left and right hemisphere lesions. Subjects included 10 young and 10 old normal adults, 14 right hemisphere patients, and 2 left hemisphere nonfluent and 7 fluent aphasic patients. Utterances were produced at a conversational speaking rate. Duration measures were taken from wide-band spectrograms. Results indicated that left hemisphere patients exhibited abnormal timing on both absolute and relative timing measures, whereas right hemisphere patients did not. Among left hemisphere patients, fluent as well as nonfluent aphasics exhibited aberrant temporal patterns. Left hemisphere patients were also more variable than right hemisphere patients which, in turn, were more variable than normals in their production of sentences. In comparison to earlier findings on timing at segment and word levels, it was found that deficit profiles varied between fluent and nonfluent aphasics as a function of the size of the linguistic unit with nonfluent aphasics being affected at the segment, word, and sentence level but fluent aphasics affected at the sentence level only. Findings are discussed in relation to issues pertaining to hemispheric specialization and the nature of timing deficits in nonfluent and fluent aphasic patients.

Adult↗
PubMed1993

Anticipatory tonal coarticulation in Thai noun compounds after unilateral brain damage.

The time course and extent of anticipatory coarticulation between tones was investigated in normal and brain-damaged Thai-speaking subjects. Subjects were classified into five groups including 11 young normal, 9 old normal, 12 right hemisphere, 9 left hemisphere fluent, and 6 left hemisphere nonfluent. Stimuli consisted of five bisyllabic noun compounds with a falling tone on the initial syllable and each of the five Thai tones (mid, low, falling, high, rising) on the final syllable. Height and slope of F0 was measured at 10% intervals throughout the duration of the initial syllable. Results indicated anticipatory effects on both height and slope of the falling tone. Height effects extended throughout from the beginning. The falling tone was generally higher when occurring before the low/rising tones than when occurring before the mid/falling/high tones. Slope effects were restricted to the terminal portion. The falling tone before low/rising tones exhibited a steeper slope than before falling/high tones. In magnitude of effect, patients with left and right hemisphere lesions were statistically indistinguishable from those of normal subjects. No differences were noted in coarticulatory patterns as a function of aphasia type. All brain-damaged speakers were more variable in F0 production than normals. Findings are interpreted to highlight properties of nonfluent aphasic speech and neurological bases of speech production.

Acoustic Stimulation↗