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.     

Acoustic cues for the perception of place of articulation in aphasia

Two experiments assessed the abilities of aphasic patients and nonaphasic controls to perceive place of articulation in stop consonants. Experiment I explored labeling and discrimination of [ba, da, ga] continua varying in formant transitions with or without an appropriate burst onset appended to the transitions. Results showed general difficulty in perceiving place of articulation for the aphasic patients. Regardless of diagnostic category or auditory language comprehension score, discrimination ability was independent of labeling ability, and discrimination functions were similar to normals even in the context of failure to reliably label the stimuli. Further there was less variability in performance for stimuli with bursts than without bursts. Experiment II measured the effects of lengthening the formant transitions on perception of place of articulation in stop consonants and on the perception of auditory analogs to the speech stimuli. Lengthening the transitions failed to improve performance for either the speech or nonspeech stimuli, and in some cases, reduced performance level. No correlation was observed between the patient's ability to perceive the speech and nonspeech stimuli.     

Contextual influences on phonetic identification in aphasia: the effects of speaking rate and semantic bias

Two experiments examined the influence of context on stop-consonant voicing identification in fluent and nonfluent aphasic patients and normal controls. Listeners were required to label the initial stop in a target word varying along a voice onset time (VOT) continuum as either voiced or voiceless ([b]/[p] or [d]/[t]). Target stimuli were presented in sentence contexts in which the rate of speech of the sentence context (Experiment 1) or the semantic bias of the context (Experiment 2) was manipulated. The results revealed that all subject groups were sensitive to the contextual influences, although the extent of the context effects varied somewhat across groups and across experiments. In addition, a number of patients in both the fluent and nonfluent aphasic groups could not consistently identify even endpoint stimuli, confirming phonetic categorization impairments previously shown in such individuals. Results are discussed with respect to the potential reliance by aphasic patients on higher level context to compensate for phonetic perception deficits.     

Compensation for Jaw Fixation by Aphasic Patients

The ability to compensate for fixation of the jaw by a bite block was investigated in 6 nonfluent aphasics, 6 fluent aphasics, and 10 normal control subjects. Acoustic analyses of the vowels [i u a æ] and fricatives [s s] revealed substantial but incomplete compensation for the perturbation in all three subject groups. Perceptual identification scores and quality ratings by naive and phonetically trained listeners indicated poorer identification of the high vowels [i u] under compensatory conditions relative to normal production. Of particular interest was the fact that all three groups of subjects exhibited similar patterns of results. The findings suggest that any deficit in speech motor programming demonstrated by the nonfluent aphasic patients did not affect compensatory abilities. Results are discussed with respect to normal speech adaptation skills and the nature of articulatory breakdown in nonfluent aphasia.     

Identification versus discrimination of distinctive features in speech perception

Dichotically presented CV syllables were presented to 24 normal subjects under two contrasting performance requirements: consonant identification and consonant discrimination. In the identification task, subjects made more errors identifying stimuli distinguished by two as opposed to one distinctive feature. Conversely, in the discrimination task, subjects made more errors for stimuli distinguished by one as opposed to two distinctive features. It was proposed that the results of the identification task reflect the degree of information load in short-term memory. The results of the discrimination task, on the other hand, reflect the degree of perceptual similarity between contrasting stimuli. Both results were accounted for within a distinctive feature framework. Analyses of the individual features which comprised one and two feature distinctions demonstrated the perceptual prominence of the feature [voice] in contrast to the two place features [compact] and [grave].     

Reaction times of severe Broca's aphasics to monaural verbal stimuli

Reaction times of nine subjects with severe Broca's aphasia were measured to verbal stimuli presented monaurally to their left or right ears. The aphasic subjects showed left-ear advantages in reaction times to verbal stimuli, paralleling dichotic findings among aphasic patients. The results are interpreted as consistent with right-hemisphere language processing.     

The influence of neighborhood density on phonetic categorization in aphasia

The present study examined the contribution of lexically based sources of information to acoustic-phonetic processing in fluent and nonfluent aphasic subjects and age-matched normals. To this end, two phonetic identification experiments were conducted which required subjects to label syllable-initial bilabial stop consonants varying along a VOT continuum as either /b/ or /p/. Factors that were controlled included the lexical status (word/nonword) and neighborhood density values corresponding to the two possible syllable interpretations in each set of stimuli. Findings indicated that all subject groups were influenced by both lexical status and neighborhood density in making phonetic categorizations. Results are discussed with respect to theories of acoustic-phonetic perception and lexical access in normal and aphasic populations.     

Feature-processing deficits following brain injury. I. Overselectivity in recognition memory for compound stimuli

A previous experiment (S. Wayland & J.E. Taplin, 1982, Brain and Language, 16, 87-108) demonstrated that aphasic subjects had particular difficulty performing a categorization task, which for normals involves abstraction of a prototype from a set of patterns and sorting of other patterns with reference to this prototype. This study extended the investigation to a recognition memory task similarly organized in categorical structure. The aim was to replicate the previous findings and to delineate the precise nature of aphasics' difficulties with such tasks. Aphasics were again found to be aberrant in performing this task in comparison with normal subjects, nonaphasic brain-injured control subjects also demonstrating a departure from normality. The results suggest that the problem for brain-injured subjects is one of overselectivity in terms of the features of the stimuli to which they respond rather than a difficulty with prototype abstraction itself.     

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.     

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.     

Feature analyzers for the phonetic dimensionstop vs. continuant

Perception of sounds along the phonetic dimensionstop vs. continuant was studied by means of a selective adaptation procedure. Subjects first identified a series of synthetic consonant-vowel syllables whose formant transitions varied in duration, slope, and amplitude characteristics. They were perceived as either [ba] or [wa]. After the initial identification test, an adapting stimulus was presented repeatedly, and then the subjects again identified the original test series. Adapting with a stop (either [ba] or [da]) led to a decrease in the number of test stimuli identified as [ba], whereas adapting with the continuant sound [wa] led to an increase in the number of [ba] identification responses. Removing the vowel portion of an adapting stimulus greatly reduced the identification shift only when the resulting stimulus was no longer perceived as speech-like. A reduction in the number of [ba] identifications occurred even when a nonspeech “stop” (the sound of a plucked string) was used as the adapting stimulus, suggesting that phonetic processing is not a necessary condition for an adaptation effect.     

Cognitive discrimination in brain-damaged adults: color vs form preference

The relative preference of color, form, and other dimensions as the basis for discrimination between stimuli has been investigated in a variety of normal and language-impaired populations. In aphasic adults, previous studies have been contradictory, and no studies of non-aphasic, brain-damaged adults have been reported. In this study color vs form preference was examined in 20 left brain-damaged, aphasic adults, 20 right brain-damaged non-aphasic adults, and 20 control subjects. Significant differences were found among all groups, with preference of color over form greatest for left brain-damaged subjects, followed by right-damaged and control subjects.     

Preserved recognition of familiar personal names in global aphasia.

Recognition of proper and common nouns was compared in four patients diagnosed with global aphasia secondary to ischemic left-hemisphere infarction. For proper noun recognition, subjects matched the spoken or written name of a famous person to a photograph, and for common nouns, subjects were tested on standardized and special word recognition tests. As expected, common noun recognition was severely compromised in the aphasic patients. In contrast, familiar personal names, despite their greater length and complexity, were recognized equally well by aphasic and normal control subjects. The right hemisphere may mediate the ability to recognize personally familiar names, as it may be specialized for establishing personally relevant environmental stimuli.     

An effect of linguistic experience: The discrimination of [r] and [l] by native speakers of Japanese and English

To test the effect of linguistic experience on the perception of a cue that is known to be effective in distinguishing between [r] and [l] in English, 21 Japanese and 39 American adults were tested on discrimination of a set of synthetic speech-like stimuli. The 13 “speech” stimuli in this set varied in the initial stationary frequency of the third formant (F3) and its subsequent transition into the vowel over a range sufficient to produce the perception of [r a] and [l a] for American subjects and to produce [r a] (which is not in phonemic contrast to [l a ]) for Japanese subjects. Discrimination tests of a comparable set of stimuli consisting of the isolated F3 components provided a “nonspeech” control. For Americans, the discrimination of the speech stimuli was nearly categorical, i.e., comparison pairs which were identified as different phonemes were discriminated with high accuracy, while pairs which were identified as the same phoneme were discriminated relatively poorly. In comparison, discrimination of speech stimuli by Japanese subjects was only slightly better than chance for all comparison pairs. Performance on nonspeech stimuli, however, was virtually identical for Japanese and American subjects; both groups showed highly accurate discrimination of all comparison pairs. These results suggest that the effect of linguistic experience is specific to perception in the “speech mode.”     

Selective adaptation of vowels

Two experiments investigating the selective adaptation of vowels examined changes in listeners’ identification functions for the vowel continuum [i-I-∈] as a function of the adapting stimulus. In Experiment I, the adapting stimuli were [i], [I], and [∈]. Both the [i] and [∈] stimuli produced significant shifts in the neighboringand distant phonetic boundaries, whereas [I] did not result in any adaptation effects. In order to explore the phonetic nature of feature adaptation in vowels, a second experiment was conducted using the adapting stimuli [gig] and [g ∈ g], which differed acoustically from the [i] and [∈] vowels on the identification continuum. Only [gig] yielded reliable adaptation effects. The results of these experiments were interpreted as suggesting arelative rather than a stableauditory mode of feature analysis in vowels and a possibly more complex auditory feature analysis for the vowel [i].     

Effects of intensity on the categorical perception of stop consonants and isolated second formant transitions

Identification and discrimination of two-formant [bae-dae-gae] and [pae-tae-kae] synthetic speech stimuli and discrimination of corresponding isolated second formant transitions (chirps) were performed by six subjects. Stimuli were presented at several intensity levels such that the intensity of the F2 transition was equated between speech and nonspeech stimuli, or the overall intensity of the stimulus was equated. At higher intensity (92 dB), b-d-g and p-t-k identification and between-category discrimination performance declined and bilabial-alveolar phonetic boundaries shifted in location on the continuum towards the F2 steady-state frequency. Between-category discrimination improved from performance at 92 dB when 92-dB speech stimuli were simultaneously masked by 60-dB speech noise; alveolar-velar boundaries shifted to a higher frequency location in the 92-dB-plus-noise condition. Chirps were discriminated categorically when presented at 58 dB, but discrimination peaks declined at higher intensities. Perceptual performance for chirps and p-t-k stimuli was very similar, and slightly inferior to performance for b-d-g stimuli, where simultaneous masking by F1 resulted in a lower effective intensity of F2. The results were related to a suggested model involving pitch comparison and transitional quality perceptual strategies.     

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.     

The effects of varying attentional demands on the word retrieval skills of adults with aphasia, right hemisphere brain damage, or no brain damage

Adults with mild aphasia, right hemisphere brain damage (RBD), or no brain damage (NBD) provided one-word phrase completions under isolation, focused attention, and divided attention conditions and in response to relatively constrained or unconstrained phrase stems. Despite comparable word retrieval accuracy among groups during the isolation condition, aphasic and RBD groups performed less accurately than the NBD group during focused and divided attention conditions. Across conditions, there were no significant differences between aphasic and RBD groups. Only aphasic subjects demonstrated a significant effect of phrase type, responding more accurately when completing constrained versus unconstrained stimuli. For aphasic and RBD groups, error type analysis indicated that semantic and phonological aspects of word retrieval were influenced by increased attentional demands. These findings suggest that for adults with aphasia or RBD, there is a negative relation between attention impairments and word retrieval abilities.     

Discourse in aphasia: Integration deficits in processing reference

The present study investigated moderately impaired aphasic subjects' ability to integrate information across sentences by having them identify antecedents for ambiguous pronouns in brief narratives. In order to disambiguate the pronouns, the subjects had to consult either textual cues and/or extratextual cues. In addition, the subjects' ability to retrieve factual information was measured by having them identify explicitly stated noun referents. The results show that the aphasic subjects had significant difficulty using textual cues to resolve referents when the referents were not readily accessible through world knowledge. The patients had little difficulty interpreting referents which were recoverable from world knowledge or were stated explicitly. The explanatory power of world knowledge effects, grammatical class effects, memory effects, and linguistic integration effects in accounting for the deficit pattern observed is considered.     

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.