Lexical tones in Thai after unilateral brain damage.

An acoustic perceptual investigation of the five lexical tones of Thai was conducted to evaluate the nature of tonal disruption in patients with unilateral lesions in the left and right hemisphere. Subjects (n = 48) included 10 young normal adults, 10 old normal adults, 11 right hemisphere nonaphasics, 9 left hemisphere fluent aphasics, and 8 left hemisphere nonfluent aphasics. The five Thai tones (mid, low, falling, high, rising) were produced in isolated monosyllables, presented for tonal identification judgments, and measured for fundamental frequency (Fo) and duration. Results of an analysis of variance indicated that left hemisphere nonfluent speakers signaled and tonal contrasts at a lower level of proficiency. The extent of their impairment varied depending on severity level of aphasia. When compared to normal speakers, tonal identification for less severe nonfluent aphasics differed more in degree than in kind, and for more severe nonfluent aphasics differed both in kind and in degree. Acoustic analysis revealed that with the exception of one left nonfluent, average Fo contours were comparable in shape across speaker groups. Variability in Fo production, however, was greater in left nonfluent speakers than in any of the other four groups of speakers. Issues are discussed regarding the extent and nature of tonal disruption in aphasia and hemispheric specialization for tone production.     

Disfluent speech associated with brain damage

The frequency and type of disfluencies in the spontaneous speech of 15 people with Broca's aphasia and right hemiplegia was studied. Two aged-matched control groups (15 nonaphasic stroke patients with left hemiplegia and 15 normals) were also studied. The frequency of disfluencies in the speech of aphasics was three times greater than that in the speech of either control group. However, most of the disfluencies uttered by aphasics were of the types commonly found in speech of normals.     

Phonemic vowel length contrasts in cerebellar disorders

Apraxia of speech and Broca's aphasia both affect voice onset time (VOT) whereas phonemic vowel length distinctions seem to be preserved. Assuming a close cooperation of anterior perisylvian language zones and the cerebellum with respect to speech timing, a similar profile of segment durations must be expected in ataxic dysarthria. In order to test this hypothesis, patients with cerebellar atrophy or cerebellar ischemia were asked to produce sentence utterances including either one of the German lexial items "Rate" (/ra:t(h)e/, 'installment'), "Ratte" (/rat(h)e/, 'rat'), "Gram" (/gra:m/, 'grief'), "Gramm" (/gram/, 'gramm'), "Taten" (/t(h)atn/, 'actions'), or "Daten" (/datn/, 'data'). At the acoustic signal, the duration of the target vowels /a/ and /a:/ as well as the VOT of the word-initial alveolar stops /d/ and /t/ were determined. In addition, a master tape comprising the target words from patients and controls in randomized order was played to three listeners for perceptual evaluation. In accordance with a previous study, first, the cerebellar subjects presented with a reduced categorical separation of the VOT of voiced and unvoiced stop consonants. Second, vowel length distinctions were only compromised in case of the minimal pair "Gram"/"Gramm." In contrast to "Rate"/"Ratte", production of the former lexical items requires coordination of several orofacial structures. Disruption of vowel length contrasts would, thus, depend upon the complexity of the underlying articulatory pattern.     

Paroxysmal speech disorder following left frontal brain damage

The patient was a 61-year-old female who suffered from the sudden attack of a speech disorder. The episodes of speech disorder lasted for less than 1 min, but occurred several times a day, paroxysmally. A CT revealed a low density area on the surface of the left frontal lobe and an EEG showed an abnormal wave at the frontoparietal area, more dominantly on the left. This condition was diagnosed as a kind of epilepsy. The paroxysmal speech disorder occurred very often during the 2 months after the first episode. However, with therapy using anticonvulsives and antibiotics, the condition began to improve after 4 months and disappeared completely after 6 months. It is assumed that the inflammatory change which occurred at the frontal lobe stimulated the supplementary motor area paroxysmally, and subsequently the speech disorder occurred as a kind of epilepsy.     

Prosodic disturbance in aphasia: Vowel length in Thai

The aim of this study is to determine to what extent a phonologically contrastive function of the prosodic feature of length is resistant to impairment in aphasia. The language chosen for investigation is Thai, a language which contrasts short and long vowels. Subjects included two Broca aphasics, one transcortical motor aphasic, one Wernicke aphasic, one conduction aphasic, one nonaphasic right-brain-damaged patient, one nonaphasic cerebellar dysarthric patient, and five normal controls. The subjects read a list of words containing short and long vowels. Vowel durations were measured from spectrograms. The results showed that the timing of vowel duration for signaling the contrast between short and long vowels remains relatively intact in nonfluent as well as fluent aphasic patients. These data are brought to bear on issues concerning the specialization of the left hemisphere for temporal processing, the contribution of the right hemisphere to the processing of nonaffective components of prosody, the nature of prosodic disturbance in Broca's aphasia and cerebellar dysarthria, and the separate disruption of prosodic features.     

Cluttering after brain damage

On the basis of published cases and of observations made in two patients, a syndrome of acquired cluttering after brain damage in adults is delineated, and a hypothesis is presented regarding the patho-physiology of the disorder.     

Neural processing of acoustic duration and phonological German vowel length: Time courses of evoked fields in response to speech and nonspeech signals

Recent experiments showed that the perception of vowel length by German listeners exhibits the characteristics of categorical perception. The present study sought to find the neural activity reflecting categorical vowel length and the short-long boundary by examining the processing of non-contrastive durations and categorical length using MEG. Using disyllabic words with varying /a/-durations and temporally-matched nonspeech stimuli, we found that each syllable elicited an M50/M100-complex. The M50-amplitude to the second syllable varied along the durational continuum, possibly reflecting the mapping of duration onto a rhythm representation. Categorical length was reflected by an additional response elicited when vowel duration exceeded the short-long boundary. This was interpreted to reflect the integration of an additional timing unit for long in contrast to short vowels. Unlike to speech, responses to short nonspeech durations lacked a M100 to the first and M50 to the second syllable, indicating different integration windows for speech and nonspeech signals.     

Reversal operations after brain damage

The ability to perform reversals—that is, the appreciation of the relationship between original and transformed states of knowledge—is critical to human thought processes. In order to assess whether a number of “special-purpose processors” are responsible for reversal operations, depending on the particular context in which the reversal is couched, or whether a single “core processing mechanism” subserves a critical aspect of reversal operations regardless of the specific context, patients with localized brain damage were asked to solve eight reversal problems. Visual and auditory reversals mediated by linguistic and non-linguistic symbol systems were presented. The findings demonstrate that patients with insult to the anterior portion of the right hemisphere encounter more difficulty performing reversals than patients with right posterior insult, Broca's aphasics, and fluent aphasics. This is regardless of the symbol system mediating the reversal, regardless of the modality of presentation, and regardless of the amount of available processing time. Subjects with insult to the posterior region of the left hemisphere or the right hemisphere also exhibit some difficulty solving reversal problems, although their difficulties appear modality specific. These data lend support to the claim that a core processing mechanism may play a critical role in the performance of reversal operations.     

Speech timing subsequent to brain damage: effects of utterance length and complexity

Acoustic analyses of syllable durations were conducted in order to address several hypotheses concerning deficits in the control of speech timing subsequent to focal brain damage. Groups of nonfluent and fluent aphasics, right-hemisphere-damaged patients, and normal controls produced monosyllabic root syllables in medial and final position in the context of short and long sentences and syntactically simple and complex sentences. Durations of the target syllable as a proportion of the utterance were compared across contexts and groups. Somewhat surprisingly, the results revealed relatively normal temporal patterns in all subject groups, with the main exception emerging for the nonfluent aphasic patients who failed to demonstrate normal phrase-final lengthening effects. Implications of the findings for theories of temporal control in brain-damaged patients are considered.     

The effects of differential vowel prolongations on perceptions of speech naturalness

Prolongation of speech sounds is currently used to modify stuttering and enhance fluency. Prolonged speech (PS) (e.g., prolonged vowels, prolongation throughout utterances) is, however, often perceived as unnatural by listeners. This study examined at which durations and in which contexts 52 college students (primary language was American English) perceived PS to be unnatural. Stimuli were limited to controlled variation in prolongation of the vowel in the middle single-syllable word of a carrier phrase (i.e., say word again). The prolongation was effected by digital waveform manipulation within the Kay Elemetrics Computerized Speech Laboratory (CSL). The listeners judged if they strongly agreed, agreed, or disagreed that the phrases sounded natural. Results indicated that the extent of vowel duration (and possibly context) does influence listener's perception of speech naturalness, findings which can be applied to facilitate fluency therapy.

Educational objectives: (1) The reader will learn about and be able to summarize the digital waveform manipulation procedure in the study. (2) The reader will learn about and be able to describe the effects of differential vowel prolongation on listener's perception of speech naturalness. (3) The reader will learn about and evaluate how differential vowel prolongation can be used to enhance fluency.     

Virtual reality in brain damage rehabilitation: review.

Given the high incidence of brain injury in the population, brain damage rehabilitation is still a relatively undeveloped field. Virtual reality (VR) has the potential to assist current rehabilitation techniques in addressing the impairments, disabilities, and handicaps associated with brain damage. The main focus of much of the exploratory research performed to date has been to investigate the use of VR in the assessment of cognitive abilities, but there is now a trend for more studies to encompass rehabilitation training strategies. This review describes studies that have used VR in the assessment and rehabilitation of specific disabilities resulting from brain injury, including executive dysfunction, memory impairments, spatial ability impairments, attention deficits, and unilateral visual neglect. In addition, it describes studies that have used VR to try to offset some of the handicaps that people experience after brain injury. Finally, a table is included which, although not an exhaustive list of everything that has been published, includes many more studies that are relevant to the use of VR in the assessment and rehabilitation of brain damage. The review concludes that the use of VR in brain damage rehabilitation is expanding dramatically and will become an integral part of cognitive assessment and rehabilitation in the future.     

The effect of vowel similarity and syllable length on acoustic memory

Darwin and Baddeley (1974) argue that the presence of recency, suffix, and modality effects are not attributable to the acoustic properties of the stimuli but, rather, to the acoustic distance between the items comprising the test series. The present study is designed to determine whether stimulus duration is a significant variable in acoustic memory. Eight different blocks of synthetic stimuli were prepared; one block each of 60 msec similar and dissimilar syllables and 190 msec similar and dissimilar syllables. The other four blocks consisted of these same vocabularies, but each list in the block had an eighth syllable suffix of the same duration as the syllables in the block. Significant recency and suffix effects are seen for dissimilar syllables of both durations. No effects are demonstrated for 60-msec similar syllables, but both of the effects are seen for 190-msec similar syllables. These results indicate that whether or not a speech sound is preserved in precategorical acoustic storage (PAS) depends upon not only the acoustic distance between the stimuli, but also on other characteristics intrinsic to the stimuli, e.g., stimulus duration.     

Comparison of associations to vowel speech sounds by English and Spanish speakers

Many psycholinguists have studied associations to vowel speech sounds. It appears that associations involving brightness and size are related to the manner in which the vowels are articulated. That is, high front vowels are judged to be bright and small, and low back vowels are judged to be dim and large. In an extension of a study by Greenberg and Jenkins (1966), 40 English-speaking and 40 Spanish-speaking adults rated nine audiotaped vowel sounds on 23 dimensions. The front-back distinction was again found for both groups. In addition, ratings for all nine vowels were similar for the two groups, which has implications for the cross-cultural universality of these associations.     

Rehabilitation of brain damage: brain plasticity and principles of guided recovery.

Rehabilitation of the damaged brain can foster reconnection of damaged neural circuits; Hebbian learning mechanisms play an important part in this. The authors propose a triage of post-lesion states, depending on the loss of connectivity in particular circuits. A small loss of connectivity will tend to lead to autonomous recovery, whereas a major loss of connectivity will lead to permanent loss of function; for such individuals, a compensatory approach to recovery is required. The third group have potentially rescuable lesioned circuits, but guided recovery depends on providing precisely targeted bottom-up and top-down inputs, maintaining adequate levels of arousal, and avoiding activation of competitor circuits that may suppress activity in target circuits. Empirical data are implemented in a neural network model, and clinical recommendations for the practice of rehabilitation following brain damage are made.     

Processing of basic speech acts following localized brain damage: a new light on the neuroanatomy of language

We examined the effect of localized brain lesions on processing of the basic speech acts (BSAs) of question, assertion, request, and command. Both left and right cerebral damage produced significant deficits relative to normal controls, and left brain damaged patients performed worse than patients with right-sided lesions. This finding argues against the common conjecture that the right hemisphere of most right-handers plays a dominant role in natural language pragmatics. In right-hemisphere damaged patients, there was no correlation between location and extent of lesion in perisylvian cortex and performance on BSAs. By contrast, processing of the different BSAs by left hemisphere-damaged patients was strongly affected by perisylvian lesion location, with each BSA showing a distinct pattern of localization. This finding raises the possibility that the classical left perisylvian localization of language functions, as measured by clinical aphasia batteries, partly reflects the localization of the BSAs required to perform these functions.