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

Neural substrates of linguistic prosody: evidence from syntactic disambiguation in the productions of brain-damaged patients

The present investigation focussed on the neural substrates underlying linguistic distinctions that are signalled by prosodic cues. A production experiment was conducted to examine the ability of left- (LHD) and right- (RHD) hemisphere-damaged patients and normal controls to use temporal and fundamental frequency cues to disambiguate sentences which include one or more Intonational Phrase level prosodic boundaries. Acoustic analyses of subjects' productions of three sentence types-parentheticals, appositives, and tags-showed that LHD speakers, compared to RHD and normal controls, exhibited impairments in the control of temporal parameters signalling phrase boundaries, including inconsistent patterns of pre-boundary lengthening and longer-than-normal pause durations in non-boundary positions. Somewhat surprisingly, a perception test presented to a group of normal native listeners showed listeners experienced greatest difficulty in identifying the presence or absence of boundaries in the productions of the RHD speakers. The findings support a cue lateralization hypothesis in which prosodic domain plays an important role.

Hemispheric lateralization effects of rhythm implementation during syllable repetitions: an fMRI study

Rhythm in terms of the modulation of syllable durations represents an information-bearing feature of verbal utterances contributing both to the meaning of a sentence (linguistic prosody) as well as a speaker's emotional expression (affective prosody). In order to delineate the neural structures subserving rhythmic shaping of speech production, functional magnetic resonance imaging (fMRI) was performed during (a) isochronous syllable repetitions and (b) production of syllable triplets with lengthening either of the initial or final unit. A cognitive subtraction approach (rhythmic versus isochronous iterations) revealed activation of right-sided perisylvian areas (superior temporal gyrus, Broca analogue and adjacent premotor cortex) as well as contralateral subcortical structures (putamen and thalamus). Presumably, these responses reflect a right-hemisphere rehearsal mechanism of rhythmic patterns and left-hemisphere monitoring of verbal output.

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.

Impaired perception of vocal emotions in Parkinson's disease: influence of speech time processing and executive functioning

Little is known about the underlying dimensions of impaired recognition of emotional prosody that is frequently observed in patients with Parkinson's disease (PD). Because patients with PD also suffer from working memory deficits and impaired time perception, the present study examined the contribution of (a) working memory (frontal executive functioning) and (b) processing of the acoustic parameter speech rate to the perception of emotional prosody in PD. Two acoustic parameters known to be important for emotional classifications (speech duration and pitch variability) were systematically varied in prosodic utterances. Twenty patients with PD and 16 healthy controls (matched for age, sex, and IQ) participated in the study. The findings imply that (1) working memory dysfunctions and perception of emotional prosody are not independent in PD, (2) PD and healthy control subjects perceived vocal emotions categorically along two acoustic manipulation continua, and (3) patients with PD show impairments in processing of speech rate information.

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.

The temporal organization of affective and non-affective speech in patients with right-hemisphere infarcts

To evaluate the right hemisphere's role in encoding speech prosody, an acoustic investigation of timing characteristics was undertaken in speakers with and without focal right-hemisphere damage (RHD) following cerebrovascular accident. Utterances varying along different prosodic dimensions (emphasis, emotion) were elicited from each speaker using a story completion paradigm, and measures of utterance rate and vowel duration were computed. Results demonstrated parallelism in how RHD and healthy individuals encoded the temporal correlates of emphasis in most experimental conditions. Differences in how RHD speakers employed temporal cues to specify some aspects of prosodic meaning (especially emotional content) were observed and corresponded to a reduction in the perceptibility of prosodic meanings when conveyed by the RHD speakers. Findings indicate that RHD individuals are most disturbed when expressing prosodic representations that vary in a graded (rather than categorical) manner in the speech signal (Blonder, Pickering, Heath et al., 1995; Pell, 1999a).