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.F₀contours 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.     

Speech sound errors in patients with conduction and Broca's aphasia

Speech sound errors exhibited by three conduction and three Broca's aphasic patients on naming and word-repetition tasks were subjected to phonemic and subphonemic analyses. In the conduction aphasic patients, errors occurred equally often on consonants and vowels in both the naming and word-repetition tasks, while in the Broca's aphasic patients errors occurred selectively on consonants. Transposition errors occurred almost as often as substitution errors in the conduction aphasic patients, while substitution errors constituted the majority of errors in the Broca's aphasic patients. The Broca's aphasic patients, as compared to the conduction aphasic patients, exhibited a markedly higher number of substitution errors occurring between phonemes separated by a single subphonemic feature on the naming task. On the basis of these findings, it was hypothesized that the differences in the error patterns of the two types of aphasia reflected differences in the underlying mechanisms of the impairment in each type.     

Impairments of nonverbal oral movements after left hemisphere damage: A followup analysis of errors

Acquisition of a task requiring the imitation of a series of nonverbal oral movements is most severely impaired in patients with aphasic disturbance. However, nonaphasic patients with left hemisphere damage also perform more poorly than patients with right hemisphere damage or normal control subjects. Analysis of the errors made on the multiple oral movements task reveals that left, but not right, hemisphere damage is highly associated with perseverative responses. Patients with right hemisphere damage do not differ significantly from normal control subjects in the acquisition of or in the type of errors made on the task. It is suggested that the left hemisphere plays an important role in the control of nonverbal oral movement production.     

Velar movements during speech in two Wernicke aphasic patients

The articulatory gestures of the velum in two Wernicke aphasic patients were examined to compare their performances with those of an apraxic patient by means of the fiberoptic technique. In contrast to the marked variability in the apraxic performance in terms of velum height and segmental duration, the two fluent aphasic subjects showed a relatively high degree of consistency in velar movements throughout several repetitions of nonsense syllables and meaningful words. In addition, both patients exhibited a normal pattern of anticipatory coarticulation. Analyses of the velar movement patterns during the speech-sound error processes of both patients suggested that these errors were not due to an impairment at the level of articulatory programming but to an error in the selection of a target phoneme.     

A kinematic analysis of anticipatory coarticulation in the speech of anterior aphasic subjects using electromagnetic articulography

An investigation was made into the extent and time course of anticipatory coarticulation in the speech of two normal and two anterior aphasic, German-speaking subjects. Both labial and velar coarticulation gestures were investigated. Subjects produced sentences containing target words contrasting in postconsonantal vowel rounding (e.g., [geli:ge]/[gely:gel]) and in nasality (e.g., [ti:de]/[ti:ne]). Speech kinematics were monitored by means of electromagnetic articulography. The data revealed that for correct productions, aphasic speakers' coarticulatory patterns were more highly variable than those of control subjects. These differences, however, were found chiefly for spatial displacement characteristics, while the temporal aspects of articulator movement necessary for anticipatory coarticulation appeared largely intact. Articulator mistiming did not appear to explain a small corpus of stop/nasal substitution errors produced by one of the aphasic speakers.     

A model-driven analysis of severity, response characteristics, and partial recovery in aphasics' picture naming

Dell, Schwartz, Martin, Saffran, and Gagnon (DSMSG; 1997) presented a computational analysis of aphasic naming that, among other things, purports to explain why some error types correlate with naming severity while others do not. It does so in terms of chance response opportunities, which differ among error types and which come into play particularly when activation levels are small. The present study looks at error frequencies in relation to severity at two points in time: at study entry and after a period of partial recovery. Results support the model's distinction between severity-sensitive errors (nonwords. formal paraphasias, and unrelated errors) and those that are severity insensitive (semantic; mixed). Additionally, we show that the degree of target overlap in nonwords is sensitive to severity but various measures of monitoring and error correction are not. While these results generally support DSMSG, effects at the level of individual patients underscore the difficulties that their model encounters in explaining some pure error dissociations.     

The Influence of Phonological Context on the Sound Errors of a Speaker with Wernicke's Aphasia

A corpus of phonological errors produced in narrative speech by a Wernicke's aphasic speaker (R.W.B.) was tested for context effects using two new methods for establishing chance baselines. A reliable anticipatory effect was found using the second method, which estimated chance from the distance between phoneme repeats in the speech sample containing the errors. Relative to this baseline, error-source distances were shorter than expected for anticipations, but not perseverations. R.W.B.'s anticipation/perseveration ratio measured intermediate between a nonaphasic error corpus and that of a more severe aphasic speaker (both reported in Schwartz et al., 1994), supporting the view that the anticipatory bias correlates to severity. Finally, R.W.B's anticipations favored word-initial segments, although errors and sources did not consistently share word or syllable position.     

The impact of frontal and non-frontal brain tumor lesions on Wisconsin Card Sorting Test performance

Several lesion and imaging studies have suggested that the Wisconsin Card Sorting Test (WCST) is a measure of executive dysfunction. However, some studies have reported that this measure has poor anatomical specificity because patients with either frontal or non-frontal focal lesions exhibit similar performance. This study examined 25 frontal, 20 non-frontal low-grade brain tumor patients, and 63 normal controls (NC) on the WCST. The frontal patients were also assigned to either a left frontal (n=10) group or a right frontal group (n=15) and compared with the non-frontal group and NC. It was hypothesized that the frontal brain tumor patients would display greater deficits on categories achieved and a higher number of perseverative errors than non-frontal brain tumor patients on the WCST. Finally, it was predicted that right frontal brain tumors would result in greater executive functioning deficits than left frontal or non-frontal brain tumors. Results indicated that the left frontal group achieved the fewest categories and committed the most perseverative errors compared to the other patient and normal control groups. In addition, the left frontal group committed significantly more perseverative errors than the right frontal group. These results suggest that the WCST is sensitive to the effects of low-grade brain tumors on executive functioning.     

A study of repetition in aphasic patients

The ability of the aphasic patient to repeat a message is a capacity of considerable diagnostic value. While it is well known that certain aphasic groups (e.g., transcortical aphasics) repeat better than other groups (e.g., conduction aphasics), possible qualitative differences among the groups have not been subjected to analysis. To secure information on repetition profiles in various aphasic subgroups, a test consisting of 11 types of items, presented under conditions of both immediate and delayed recall, was administered to eight groups of aphasic patients. The results documented a significant difference across aphasic groups, one related to site of lesion but not to severity of comprehension defect. Performance proved to be a joint product of the length and the meaningfulness of the stimulus items. The delayed condition aided Broca's aphasics and impeded anomic aphasics; in addition, nonsense syllables proved to be easier on immediate recall, while meaningful stimuli, particularly those which were number related, were relatively easier on delayed recall. Finally, sound errors were more likely to be made by Broca's and “mixed anterior” aphasics, while meaning errors were particularly prominent among conduction aphasics. These results are discussed in terms of the mechanisms which may mediate repetition in aphasic patients.     

Crossed Aphasia in a Dextral: A Test of the Alexander–Annett Theory of Anomalous Organization of Brain Function

A case of crossed aphasia is presented in a strongly right-handed 77-year-old white female without history of familial sinistrality or prior neurological illness. She developed a right middle cerebral artery infarction documented by CT and accompanied by obvious clinical signs of a conduction aphasia with some resolution but continuing obvious language defect after 9 weeks in rehabilitation. Comprehensive neuropsychological and aphasia testing suggested anomalous lateralization of phonologic-output aspects of language, emotional prosody, motor planning and body schema modules with usual lateralization of lexical–semantic aspects of language and visuo-spatial functions. Experimental validation of the uncrossed lexical–semantic aspects of language using tachistoscope methods found support for the Alexander–Annett theory that different aspects of language can be dissociated in their lateralization. The subject had difficulty identifying a semantic associate of a picture presented to the left visual field (7 errors out of 10) relative to right visual field presentation (2 errors out of 10). Bilateral free naming errors (6 and 5 errors in the left and right visual fields, respectively) occurred consistent with the aphasic presentation, suggesting phonologic-output dysfunction from the right cerebral vascular accident. Implications of the results for aphasia classification are discussed.     

Confrontation naming impairment in dementia

In tone languages pitch variations (tones) serve to distinguish the lexical meanings of words. This study was conducted to examine the extent and nature of impairment in the perception of tones by aphasic patients who were monolingual speakers of Thai, a tone language which has five contrastive tones (mid, low, falling, high, rising). Six subjects participated in the study: two Broca aphasics, one transcortical motor aphasic, one conduction aphasic, one right brain-damaged nonaphasic, and one normal control. Three sets of stimuli (two real-speech, one synthetic-speech) were presented for identification, each set containing five Thai words minimally distinguished by tone. Results of the perception tests indicated that the performance of all four left brain-damaged aphasics differed significantly from that of the normal control, while the performance of the right brain-damaged nonaphasic did not. The normal performance of the right brain-damaged nonaphasic patient on this tone identification task suggests that deficits in the perception of tone exhibited by left brain-damaged patients can be attributed specifically to pathology in the language dominant hemisphere rather than to a general brain-damage effect. No difference in performance among the left brain-damaged patients could be attributed to a specific type of aphasic syndrome. The pattern of tonal confusions of the aphasics in comparison to that of normals suggests that their deficit is primarily quantitative rather than qualitative. Although two (mid, low) of the five tones accounted for a large percentage of the aphasics' errors, no uniform rank order of tones in terms of identifiability could be established across aphasic subjects, which suggests that their deficit is general to all five tones rather than selective to individual tones.     

Voice onset time in aphasia: Thai. I. Perception

This study investigated left brain-damaged aphasic and right brain-damaged non-aphasic patients' ability to label synthetic speech continua differing in voice onset time (VOT) at three places of articulation. The language chosen for investigation was Thai, which exhibits 3 contrasting labial and apical stop categories (voiced, voiceless unaspirated, voiceless aspirated) and 2 contrasting velar stop categories (voiceless unaspirated, voiceless aspirated). Results of the labelling task indicated an impairment in VOT perception at all three places of articulation across clinical types of aphasia. Normal performance by the right brain-damaged patient indicated that deficits in VOT perception can be attributed to pathology specific to the language-dominant hemisphere. No relation was found between the aphasic patient's level of auditory language comprehension and his performance on the VOT perception task. It is suggested that the aphasics' impairment reflects a deficit in phonological processing at the linguistic level.     

Functional cerebral asymmetry in hostility: a dual task approach with fluency and cardiovascular regulation

The influence of hostility levels on verbal and nonverbal fluency, and the concurrent cerebral regulation of autonomic nervous system functioning was examined in 48 right-handed males, half classified as low-hostile, and half as high-hostile. Recent research has supported inhibitory roles for the anterior right cerebrum in sympathetic regulation, and the anterior left cerebrum in parasympathetic regulation. Two neuropsychological tests purportedly mediated by left and right anterior cerebral systems, respectively, are the Controlled Oral Word Association Test and the Ruff Figural Fluency Test. Fluency and perseverative errors were assessed using these measures. Systolic and diastolic blood pressure, and heart rate were assessed with a digital blood pressure meter. It was predicted that high-hostile men would evidence interference on cardiovascular regulation concurrent with the nonverbal fluency task in comparison to low-hostile males. Further, interference was expected to manifest in the cognitive variable with more perseverative errors on the nonverbal fluency task in high-hostile males than in low-hostile males. The results support a capacity-limited prediction. High-hostile males evidenced significantly heightened systolic blood pressure during the nonverbal fluency task in comparison with low-hostile males. Further, high-hostile males displayed more perseverative errors in nonverbal fluency than did the low-hostile males. These results support the expectation that differences exist between high- and low-hostile males for right frontal functioning. These findings were discussed within the proposed anterior-posterior inhibition model of hostility.     

A Search for the Optimal Stimulus

How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an “apparent” shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles.     

Orthographic effects in the word substitutions of aphasic patients: an epidemic of right neglect dyslexia?

Aphasic patients with reading impairments frequently substitute incorrect real words for target words when reading aloud. Many of these word substitutions have substantial orthographic overlap with their targets and are classified as "visual errors" (i.e., sharing 50% of targets' letters in the same relative position). Fifteen chronic aphasic patients read a battery of words and non-words; non-word reading was poor for all patients, and more than 50% of errors on words involved the substitution of a non-target word. An investigation of the factors conditioning these word substitutions, as well as the production of visual errors, identified a number of similarities to patterns previously reported for patients with right neglect dyslexia, which has been said to occur relatively rarely. These included a strong tendency for errors to overlap targets in initial letter positions, maintenance of target length in errors, and the substitution of words higher in imageability than targets. It is proposed that left hemisphere damage frequently leads to disruption of a level of representation for written words in which letter position is ordinally coded, resulting in exacerbation of a normal processing advantage for early letter positions. A computational model is discussed that incorporates this level of representation and successfully simulates relevant normal and patient data.     

The classifier problem in Chinese aphasia

In recent years, research on the relationship between brain organization and language processing has benefited tremendously from cross-linguistic comparisons of language disorders among different types of aphasic patients. Results from these cross-linguistic studies have shown that the same aphasic syndromes often look very different from one language to another, suggesting that language-specific knowledge is largely preserved in Broca's and Wernicke's aphasics. In this paper, Chinese aphasic patients were examined with respect to their (in)ability to use classifiers in a noun phrase. The Chinese language, in addition to its lack of verb conjugation and an absence of noun declension, is exceptional in yet another respect: articles, numerals, and other such modifiers cannot directly precede their associated nouns, there has to be an intervening morpheme called a classifier. The appropriate usage of nominal classifiers is considered to be one of the most difficult aspects of Chinese grammar. Our examination of Chinese aphasic patients revealed two essential points. First, Chinese aphasic patients experience difficulty in the production of nominal classifiers, committing a significant number of errors of omission and/or substitution. Second, two different kinds of substitution errors are observed in Broca's and Wernicke's patients, and the detailed analysis of the difference demands a rethinking of the distinction between agrammatism and paragrammatism. The result adds to a growing body of evidence suggesting that grammar is impaired in fluent as well as nonfluent aphasia.     

Error Types in Ideomotor Apraxia: A Qualitative Analysis

Seventeen brain-damaged subjects with dominant hemisphere pathology and 24 matched control subjects were asked to perform simple familiar gestures under four conditions: (1) verbal command (pantomime), (2) imitation, (3) with the actual object, and (4) verbal command a second time. The subjects subsequently watched a video of an actor performing simple movements and decided whether or not these were performed accurately. The gestural production task was videoed and analyzed for error type. Error type remained consistent over the four task conditions, although subgroups of patients made different types of errors. One group of patients with Ideomotor Apraxia (IMA) made more errors but of the same type as the controls, i.e., movement-related errors and the use of "body part as object" (BPO). The second group made mainly substituted (i.e. unrelated) movements and perseverative errors. The second group of subjects was also poorer at discriminating incorrectly performed movements in the recognition task. BPO errors were commonly made by the control group and they were also chosen as correct in the recognition task. This indicated that use of BPO may reflect a convention in symbolising gestures rather than pathology. The performance of the IMA subjects was discussed in relation to current theories of the mechanisms underlying apraxia.     

Origins of Paraphasias in Deep Dysphasia: Testing the Consequences of a Decay Impairment to an Interactive Spreading Activation Model of Lexical Retrieval

This study investigates an account of atypical error patterns within the framework of an interactive spreading activation model. Martin and Saffran (1992) described a patient, NC, whose error pattern was unusual for the occurrence of higher rates of form-related than meaning-related word substitutions in naming and the production of semantic errors in repetition. They proposed that NC′s error pattern could be accounted for by a pathologically rapid decay of primed nodes in the semantic-lexical-phonological network that shifts the probabilities of error outcome in lexical retrieval. In the present study, Martin and Saffran′s account was tested and supported in a series of simulations that reproduce essential features of NC′s lexical error pattern in naming and repetition. Also described here are the results of a longitudinal study of NC′s naming and repetition, which revealed a shift in relative lexical error rates toward a qualitatively normal pattern. This change in error pattern was simulated by assuming that recovery reflects resolution of the rapid decay rate toward normal levels. The patient data and computational studies are discussed in terms of their significance for the understanding of aphasic impairments and their implications for models of lexical retrieval.     

Switching between spatial stimulus-response mappings: a developmental study of cognitive flexibility

Four different age groups (8-9-year-olds, 11-12-year-olds, 13-15-year-olds and young adults) performed a spatial rule-switch task in which the sorting rule had to be detected on the basis of feedback or on the basis of switch cues. Performance errors were examined on the basis of a recently introduced method of error scoring for the Wisconsin Card Sorting Task (WCST; Barcelo & Knight, 2002). This method allowed us to differentiate between errors due to failure-to-maintain-set (distraction errors) and errors due to failure-to-switch-set (perseverative errors). The anticipated age differences in performance errors were most pronounced for perseverative errors between 8-9 years and 11-12 years, but for distraction errors adult levels were not reached until 13-15 years. These findings were interpreted to support the notion that set switching and set maintenance follow distinct developmental trajectories.