Auditory event-related potential probes and behavioral measures of aphasia

This study examined the relationship between an auditory event-related potential probe technique measure of differential hemispheric processing and traditional tests of aphasia in aphasic patients. Subjects were 10 aphasic and 10 normal adult males. The results of the electrophysiological measures indicated that the aphasic subjects responded differently from the normal group particularly when the task required processing of verbal information. During the verbal task the aphasic group showed higher amplitude right hemisphere responses as compared to left. The normal group showed little hemispheric task related asymmetries. The pattern of electrical asymmetry in the aphasic group seems to be an indicator of severity as measured by traditional aphasia examinations.     

Eye-position aftereffects of backward head tilt manifested by illusory visual direction

Three experiments showed posttest-minus-pretest shifts in subjective straight-ahead eye position when subjects read for 3, 6, or 9 min with their heads tilted back 20° from upright. These shifts were significant relative to control conditions in which subjects read with their heads upright. All subjects read with the same straight-ahead eye-in-head position. Variability-reducing procedures were developed to provide better measures over Experiments 1, 2. and 3. Explanations in terms of deliberate compensation, head-position asymmetries, eye-position asymmetries, and progressive error were ruled out. It was hypothesized that the shifts were caused by negative aftereffects of compensation for the doll reflex. The doll reflex rotates the eyes down without central registration. causing an upward illusory shift of visual direction similar to what is caused by wedge prisms. Perceptual-motor adaptation to this shift, i.e., doll adaptation, causes an illusory shift in the opposite direction when the head is returned to upright.     

Word Length and Vowel Duration in Apraxia of Speech: The Use of Relative Measures

Previous research has established that the duration of stressed word stem vowels is shorter in polysyllabic words than in monosyllabic words for normal speakers and for speakers with aphasia and apraxia of speech (AOS). However, the results are inconsistent across studies with regard to the magnitude and pattern of the duration reduction for apraxic speakers. We hypothesized that this inconsistency may be explained based on different relative measures of duration reduction. A speech sample was obtained from 10 aphasic speakers with AOS, 10 aphasic speakers without AOS, and 10 normal controls. As predicted, the use of two different relative measures resulted in different vowel reduction patterns, both of which were consistent with previous reports. The results further indicate that the production of polysyllabic words is particularly taxing in AOS and is associated with a substantial reduction of speaking rate compared to other aphasic and normal speakers.     

Anticipatory coarticulation in aphasia: acoustic and perceptual data

Two experiments investigated speech motor planning in aphasia by contrasting the degree of labial and lingual anticipatory coarticulation evident in normal subjects' speech with that found in the speech of aphasic subjects. In the first experiment, Linear Predictive Coding (LPC) analyses were conducted for the initial consonants of CV [si su ti tu ki ku] and CCV [sti stu ski sku] productions by 6 normal and 10 aphasic (5 anterior, 5 posterior) subjects. For normal subjects' productions, reliable coarticulatory shift was found for almost all measurements, indicating that acoustic correlates for anticipatory coarticulation obtain for [s], [t], and [k] in a prevocalic environment, as well as when [s] is the initial consonant of a CCV syllable. The data for the aphasic subjects were statistically indistinguishable from those of the normal subject group, and there were no differences noted as a function of aphasia type. In the second experiment, a subset of the consonantal stimuli produced by the normal and aphasic subjects was presented to a group of 10 naive listeners for a vowel identification task. Listeners were able to identify the productions of all subjects at a level well above chance. In addition, small but statistically significant Group differences were observed, with the [sV], [skV], and [tV] productions by anterior aphasics showing significantly lower perceptual scores than those of normal subjects.     

Feature analysis and the token test

In a picture-matching task pictures of objects had to be arranged into pairs by aphasic and nonaphasic patients and normal controls. Aphasic patients were also given the Token Test. Correlation between the rank order of error scores in both tests was highly significant in aphasic patients. The pictures were also given to a normal group for free matching. Overlapping of normal performance on free matching and aphasic performance on bound matching occurred. We hypothesized that aphasic impairment was due to a difficulty in calling up associations, difficulty in feature analysis, and in moving from one concept to another. These findings are discussed in the light of abilities needed for Token Test performance. The results indicate that the traditionally presumed fundamental difference between verbal and nonverbal cognitive tasks is rather unsatisfactory.     

Comparison of the performances of a fluent and a nonfluent aphasic on a pantomimic referential task

The pantomimic performances of a typical Broca's (nonfluent) and Wernicke's (fluent) aphasic were compared with each other and with four normal control subjects on a simple task of nonverbal referential communication. Both aphasic subjects demonstrated only about 50% accuracy in their pantomimic communication. Also, measures were obtained of the motoric fluency of the pantomimes of all subjects and comparisons were made between the fluent and nonfluent aphasics. These measures demonstrated distinct differences in the fluency patterns of the pantomimes of the two aphasic subjects similar to the differences in speech fluency which distinguish and characterize these two types of aphasia; that is, the fluent aphasic pantomimed fluently and like the control subjects and the nonfluent aphasic pantomimed nonfluently. The quantitative and qualitative similarities in the fluency patterns of the speech and the pantomimic behaviors of the aphasic subjects are discussed in terms of their implications for a definition of aphasia.     

The effect of pictorial context on sentence memory in Broca's and Wernicke's aphasia

Eighteen aphasic patients (8 Broca's and 10 Wernicke's aphasics), 11 right hemisphere damaged patients and 12 normal subjects were tested to assess the effect of pictorial context on verbal memory with a sentence recognition task. The subjects were read aloud a stimulus sentence describing a simple event and simultaneously shown a picture congruent or incongruent with the sentence. Immediately following or after an interval of 30 sec, the subjects were read aloud a second sentence and asked to judge whether this sentence was the same or different from the stimulus sentence. The results indicated that verbal memory was better retained in supportive situations than in distracting situations, and that this contextual effect was greater in aphasic patients than in any of the other groups. Verbal memory declined rapidly after an interval in aphasic patients, but not in normal subjects. The Broca's and the Wernicke's aphasics demonstrated different performance patterns when semantic analysis of sentences was critical.     

Rhyme Priming in Aphasia: The Role of Phonology in Lexical Access

The present experiment was conducted to explore the facilitory effects of rhyme in lexical processing in brain-damaged individuals. Normal subjects and non-fluent and fluent aphasic subjects performed auditory lexical decision and rhyme judgement tasks, in which prime-target pairs were phonologically related (either identical or rhyming) or unrelated. Results revealed rhyme facilitation of lexical decisions to real-word targets for normal and non-fluent aphasic subjects; for fluent aphasic subjects, results were equivocal. In the rhyme judgement task, facilitory effects of rhyme were found for all three groups with real-word targets. None of the groups showed clear rhyme facilitation effects with non-word targets in either task. Findings are discussed with reference to the role of phonology in lexical processing in normal and aphasic populations.     

Nonspeech and speech processing skills in patients with aphasia and apraxia of speech

Nonspeech and speech auditory processing skills as well as internal speech processing skills were assessed among four patients with acquired "pure" apraxia of speech, 10 with acquired aphasia, 10 with aphasia plus apraxia of speech, and 11 neurologically normal adults. Fourteen tasks were administered and performances on 68 variables were examined using both nonparametric and parametric analyses controlling for the effects of advancing age and associated hearing loss. In all cases, the "pure" apractic patients performed as normal subjects. Few differences were noted among the performances of the aphasic and aphasic-apractic subjects. Results led to three major conclusions: (1) apraxia of speech is a disorder distinct from aphasia; (2) aphasic individuals, despite locus of lesion, demonstrate disabilities for processing nonspeech and speech materials presented auditorily and for analytically evaluating speech evoked internally; and (3) aphasic individuals demonstrating similar severity levels of language impairment show similar performance patterns for these types of processing tasks, despite locus of lesion or coexistence of apraxia of speech.     

A comparison of the codeswitching patterns of aphasic and neurologically normal bilingual speakers of English and Spanish

Conversational discourse samples were obtained from four aphasic and four neurologically normal Hispanic bilinguals in monolingual English, monolingual Spanish, and bilingual contexts to identify codeswitching patterns. Analysis of the samples based on the Matrix Language Frame (MLF) Model (Myers-Scotton, 1993a) revealed consistent matching of the language context by the aphasic and normal subjects. The aphasic subjects demonstrated a greater frequency of MLF constituents and codeswitching patterns not evident in the speech samples of the normal subjects. Results suggest an increased dependence on both languages for communication following neurological impairment.     

An Acoustic Analysis of Rate of Speech Effects on Vowel Production in Aphasia

The present investigation examined the production of tense and lax vowel duration differences at two speaking rates in the speech of 10 nonfluent aphasics, 8 fluent aphasics, and 10 normal control subjects. Subjects produced four repetitions of each of the vowels [i e æ o u I ε υ Λ] at each speaking rate. Acoustic analyses revealed that subjects in all three groups were able to manipulate overall rate of speech. In addition, normal controls and fluent aphasic subjects produced vowels under the fast rate condition which were significantly shorter than those under the slow rate condition. Despite a change in overall speaking rate, the nonfluent aphasics did not exhibit a significant difference in vowel duration at the two rates of speech, suggesting a deficit in the implementation of this temporal parameter. Both normal controls and fluent aphasic patients produced nonoverlapping distributions of tense and lax vowels at both speaking rates. In contrast, the nonfluent aphasics demonstrated a great deal of overlap in the distribution of tense and lax vowel durations at the fast rate. Results are discussed in relation to the nature of the speech production deficits in nonfluent and fluent aphasic patients.     

Cognitive distancing in mediated categorization in aphasia

Individuals with fluent and nonfluent aphasia and a matched group of aged normal subjects participated in mediated categorization tasks dealing with two levels of cognitive distancing. Moreover, the categorization tasks entailed the utilization of focal and peripheral exemplars. Fluent aphasic subjects had significantly more difficulty than nonfluent aphasic and normal subjects. All subjects had significantly more difficulty with pictures than actual objects. Peripheral exemplars were used less often than focal exemplars. It was speculated that some of these results may reflect a degenerative process of aging.     

Effect of structured visual environments on apparent eye level

Each of 12 subjects set a binocularly viewed target to apparent eye level; the target was projected on the rear wall of an open box, the floor of which was horizontal or pitched up and down at angles of 7.5 degrees and 15 degrees. Settings of the target were systematically biased by 60% of the pitch angle when the interior of the box was illuminated, but by only 5% when the interior of the box was darkened. Within-subjects variability of the settings was less under illuminated viewing conditions than in the dark, but was independent of box pitch angle. In a second experiment, 11 subjects were tested with an illuminated pitched box, yielding biases of 53% and 49% for binocular and monocular viewing conditions, respectively. The results are discussed in terms of individual and interactive effects of optical, gravitational, and extraretinal eye-position information in determining judgements of eye level.     

Word-association responses to time-altered stimuli by schizophrenic adults

This research addressed the relationship between the speed of presentation of stimuli through the auditory and visual modalities and the number of syntagmatic and paradigmatic word-association responses of 49 chronic undifferentiated schizophrenic adults. In word-association tests administered to subjects stimuli were balanced for frequency of occurrence in written English language (frequent, infrequent), word length (long, short), abstraction level (low, medium, high), and part of speech (noun, verb, adjective). The words were presented auditorily at normal speed (equivalent to 10 phonemes per second) and at half speed (equivalent to 5 phonemes per second) speech. Words were also presented visually, using a tachistoscope, at extended fixation speed (equivalent to 1,000 msec.) and at sweep speed (equivalent to 10 msec.). More paradigmatic responses occurred on word stimuli if nouns, long, and frequently occurring presented auditorily; and if concrete, nouns, and presented slowly and visually. Results were compared to previously reported data for aphasic and normal adults, and differentiating features and clinical implications were discussed.     

The processing of the sounds and meanings of ongoing speech by aphasic subjects

The ability of aphasic subjects to process the sounds and meanings of ongoing speech was tested. Subjects, 10 aphasic and 20 control, heard test sentences which contained one member of phonemically similar word pairs in one of three semantic contexts: congruent, neutral, and noncongruent. Immediately after hearing a sentence, subjects were to indicate which member of the word pair had been in the sentence. All subject groups had similar overall patterns of response to the different semantic contexts. The division of aphasic subjects into groups of high and low comprehenders revealed response differences. High comprehending aphasic subjects, like control subjects, demonstrated interactive processing of the sounds and meaning of speech while low comprehending aphasic subjects did not.     

On-line monitoring of eye-position signals in contingent and noncontingent paradigms

This paper presents a research methodology for the study of human attentional and perceptual processes by means of on-line monitoring of eye-position signals. The first part of the presentation considers techniques by which commercially available apparatus may be interfaced to a minicomputer for purposes of monitoring eye-position signals during psychological experiments. Hardware and software techniques related to automating the calibration, recording, and analysis of eye-position data are discussed. The second part of the paper discusses a more advanced research methodology, one in which visual stimuli are contingent upon momentary eye-position signals. The methodology is appropriate to a variety of studies in which eye movements are considered to be part of an attentional control system. Several experimental applications are described. The implementation of eye-position-stimulus contingencies on a small computer poses additional technical problems, several of which are discussed.     

Gaze-dependent deviation in pointing induced by transcranial magnetic stimulation over the human posterior parietal cortex

Signals arising from the saccadic system influence the planning and generation of pointing movements, and the posterior parietal cortex (PPC) appears to play a vital role in that interaction. The authors demonstrate in the present study that during visual fixation, eye-position signals can dominate pointing responses when the activity in the PPC contralateral to the moving limb is disrupted with transcranial magnetic stimulation (TMS). In particular, when presented with targets in peripheral vision, participants (N=5) exposed to TMS over the PPC failed to show the normal pattern of responses in which pointing movements end up farther away from the goal target. Instead, they tended to point more toward the current point of visual fixation. Those results suggest that the PPC is involved in integrating eye-position and visual information to affect reaching in the contralateral arm.     

Altered patterns of word associations in dementia and aphasia

The word associations of 38 demented, 17 aphasic, and 22 normal subjects were studied. Both normal and brain-injured subjects appear to make judgments about the grammatical class of the word stimulus. Certain stimulus words (especially nouns and adjectives) elicit paradigmatic responses whereas other words (especially verbs and adverbs) elicit syntagmatic responses. The mechanism producing syntagmatic responses seems relatively resistant to deterioration in dementia or aphasia. However, in dementia the mechanism that generates paradigmatic responses becomes progressively less efficient (possibly due to a loss of semantic markers) and consequently more random (idiosyncratic) responses emerge. Perseverative responses, inhibited in normal subjects, are more prevalent in dementia. Anomic aphasics show a pattern of word associations similar to that of subjects with mild dementia. Broca's aphasics, while making fewer paradigmatic associations than normals, retain enough self-monitoring mechanisms so that few idiosyncratic and perseverative responses are made while more null responses occur. Wernicke's aphasics show a marked shift away from a paradigmatic word association strategy, possibly due to an inability to access semantic markers or a true loss of these markers. Metalinguistic deficits (i.e., a failure to adopt an appropriate strategy) may also contribute to this shift away from paradigmatic associations. Furthermore, a disruption of self-monitoring mechanisms in Wernicke's aphasia leads to an increase in perseverative and idiosyncratic responses.     

Aphasics' appreciation of hierarchical semantic categories

The mental representative structure of hierarchically ordered semantic categories was explored with 66 aphasic patients and 60 normal adults by a word-verification task. Four words concerning living things and 10 line drawings depicting an object were prepared as stimuli. All possible pairings of each of the four words with each of the 10 line drawings were made to be verified. The results indicated that subjective category domains were more diffusive in aphasic patients than in normal adults, and that this alteration was exclusively due to increase of peripheral members, but not of central members. It was also revealed that normative category boundaries may be preserved vestigially or incompletely in aphasic patients except the severe fluent subgroup, in whom there may be profound disintegration of boundaries. On the other hand, some common features concerning intracategorical structure and preference among levels of abstraction across normal adults and aphasic patients permit the hypothesis that aphasic patients may retain partially normal semantic knowledge.     

Word-finding abilities of three types of aphasic subjects

Word-finding difficulties are often observed among different types of aphasic patients. This investigation analyzed the word-finding abilities of 30 aphasic subjects (10 Broca's, 10 Wernicke's, and 10 anomic). Forty nouns counterbalanced according to word length and frequency of occurrence in English language usage were used as stimuli and presented through four modalities (oral expression, writing, auditory comprehension, and reading comprehension). It was expected that patterns of word finding abilities would help in the classification of the different types of aphasia. In addition, long words and less frequently occurring words in English language usage should prove more difficult in word-finding ability, regardless of modality. The results of this study found long words and less frequent words were more difficult for aphasic subjects. Among the modalities, long words were significantly harder than short words for the writing modality only. It was also found that semantic errors were the most common errors for all types of aphasic subjects. Broca's subjects produced significantly moreno response errors in oral expression; Wernicke's subjects produced significantly more semantic and phonemic errors in reading comprehension; and, Wernicke's subjects produced significantly more unrelated errors in both oral expression and reading comprehension. Clinical implications were also discussed.The present study was based on a doctoral dissertation completed at the City University of New York in partial fulfillment of the requirements of the doctoral degree in Speech and Hearing Sciences by the first author under the direction of the second author. The authors wish to thank Dr. Louis J. Gerstman for his assistance with the statistical analysis of this research and Dr. Robert Goldfarb for all his helpful suggestions and editorial comments.