Journal of Speech and Hearing Research, Volume 34, 67-80, February 1991

Perceptual Characteristics of Vowel and Prosody Production in Apraxic, Aphasic, and Dysarthric Speakers Katharine Odell Malcolm R. McNeil Department of Communicative Disorders University of WisconsinMadison

John C. Rosenbek Speech Pathology and Audiology Service Veterans Administration Medical Center Madison, Wisconsin

Linda Hunter Department of African Languages and Linguistics University of Wisconsin-Madison

Narrow phonetic transcriptions and prosodic judgments were made of single-word imitations by apraxic (AOS), conduction aphasic (CA), and ataxic dysarthric (AD) speakers. AOS and AD subjects showed similar vowel error patterns, particularly predominant errors in low, tense, and back vowels, more distortions than other types of vowel errors, and predominant errors ininitial position of words and inmonosyllabic words. The CA subjects displayed a different vowel error pattern, notably more substitutions than distortions, more errors in polysyllabic than monosyllabic words, and more errors in noninitial than initial positions of words. Analysis of prosodic features identifiable at the single-word level (e.g., syllabic stress, juncture, and struggles to initiate or complete productions) indicated that syllabic stress errors and more difficulty initiating than completing word production were characteristic of AOS and AD but not CA subjects. KEY WORDS: consonant articulation, perceptual analysis, apraxia of speech, ataxic dysarthria, conduction aphasia

Apraxia of speech, ataxic dysarthria, and conduction aphasia have been described as presenting disturbances in selected aspects of speech prosody and vowel production. Apraxia of speech exhibits both equalization of stress (Darley, Aronson, & Brown, 1975; Kent & Rosenbek, 1982) and distorted vowel articulation (Canter, Trost, & Burns, 1985; LaPointe & Johns, 1975; Monoi, Fukusako, Itoh, & Sasanuma, 1983; Trost & Canter, 1974). Core features of ataxic dysarthria include impairments in vowel articulation and the related feature of "excess and equal" stress (Darley et al., 1975). Descriptions of conduction aphasic speech mention vowel misarticulations (Monoi et al., 1983) but emphasize the paradoxical perception of both "fluent" speech and the irregular interruptions in fluent speech of hesitations and serial repetitions of partial and whole words that are assumed to be associated with efforts to correct literal paraphasic errors (Benson, 1979; Brown, 1975; Goodglass & Kaplan, 1983; Tzortzis & Albert, 1974; Yorkston & Beukelman, 1979). Because these descriptions are general and based on limited data sets, the current study was designed to provide detailed perceptual analyses of vowel and prosody production in these groups. Proficiency of vowel production was analyzed by narrow phonetic transcription and characterization of the nature of vowel errors. Judgment of the accurate production of prosody, defined in a general sense as the melody of language (Monrad-Krohn, 1947), was sought through analysis of selected segmental, syllabic, and word-level features considered by many investigators to contribute to a perception of prosody. These features included variations in perceived syllable stress manifested as increased intensity, tone (pitch), and/or duration (length) that are identifiable at the segment and syllabic levels (Crystal, 1969; Hyman, 1975; Lehiste, 1970; Rabiner, Levitt, & Rosenberg, 1969); phonetic and syllabic transitions (Canter C 1991, American Speech-Language-Hearing Association

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et al., 1985; Square, Darley, & Sommers, 1982); and difficulties in initiating or completing articulatory attempts (Harrington, 1988; Wingate, 1969). This study is part of a larger research effort to describe the perceptual, acoustic, and kinematic characteristics of apraxia of speech (AOS) and to distinguish these features in AOS from similar attributes in ataxic dysarthria and conduction aphasia, each of which resembles AOS in selected speech features. Subjects were carefully selected as representative of each group, with the expectation of a finer differentiation of speech qualities among the groups. All analyses were derived from imitations of single words that increased in number of syllables, because production of such words was expected to highlight production difficulties in apraxic speakers, the pivotal group in this research effort. Furthermore, these analyses were designed to complement the fine-grained perceptual studies of consonant articulation in the identical speech stimuli in the same AOS subjects (Odell, McNeil, Rosenbek, & Hunter, 1990) and comparable forthcoming consonant studies involving the subjects in the other two groups. Thus, categories of analysis selected for this study paralleled, in large measure, those in the consonant study. As a unit, these segmental and prosodic analyses constitute initial steps in a series of investigations designed to describe speech characteristics of phrase- and discourse-level production within and among these subject populations.

Methods Subjects Twelve subjects participated in the study, 4 in each of the following diagnostic categories: apraxia of speech (AOS), conduction aphasia (CA), and ataxic dysarthria (AD). Potential subjects in each category were initially referred by experienced speech-language pathologists in other medical and university centers. Many of those referred did not meet the stringent criteria for selection and were excluded from the study. Final identification and selection of the 12 subjects was made by consensus between two certified speechlanguage pathologists experienced in the diagnosis and differentiation of these disorders. All subjects were native speakers of English with premorbid General American Speech dialects. Each had speech discrimination scores of 70% or better at 40 dB HL in at least one ear. Lesion location in AOS and CA subjects was documented by CT scan for descriptive purposes only and was not a part of the selection criteria. Scans were later read by a board-certified neurologist, trained and reliable in reading brain scans. A summary of the lesion data is shown in Table 1. AD subjects presented with a variety of cerebellar diseases, all confirmed by neurological examination. Judgments of the presence of AOS, CA, and AD were made perceptually on the basis of live as well as audio- and videotaped speech performances on the Apraxia Battery for Adults (ABA) (Dabul, 1979), conversational speech, the Cookie Theft description from the Boston Diagnostic Aphasia Examination (BDAE) (Goodglass & Kap-

34 67-80 February 991

lan, 1983)1 and repetition of the subject's own utterances on this descriptive task presented orally to him or her in the same phrasal units of the original production, and the verbal subtests of the Porch Index of Communicative Ability (PICA) (Porch, 1967). Evidence of AOS was as follows: effortful attempts to initiate speech; sound substitutions; variability in repeated speech trials; and articulatory agility, phrase length, and melodic line ratings between 1 and 4 on the BDAE rating of speech characteristics. Repetition was judged to be equal or superior to elicited or spontaneous speech on selected tasks. Judgment was based on the BDAE sentence repetition (High Probability subtest) and a comparison of the orthographic transcription of the Cookie Theft picture description and the repetition of the same utterances, presented orally to each subject in the same phrasal units in which they were initially uttered. The absence of aphasia, based on Darley's (1982) definition, was determined by an average performance above the first percentile for normal subjects on the pantomime, auditory comprehension, visual matching, and reading comprehension subtests of the PICA. The verbal and graphic subtests were removed from the overall score because of potential misinterpretation of these subtests in subjects who may have had oral and limb motor deficits accompanying language deficits. On the auditory comprehension subtests of the BDAE, subjects performed at or above the recommended cutoff point for normal subjects (Borod, Goodglass, & Kaplan, 1980). Subjects did not display agrammatic syntax, dysnomia, or other language impairments in oral speech. In summary, the battery of tests administered detected no evidence of aphasia in these apraxic subjects. The absence of dysarthria was determined by performance on a structuralfunctional speech examination (S-F) (Rosenbek & Wertz, 1976), administered by two experienced speech-language pathologists, and by neurological examination. Evidence of CA was as follows: frequent sound substitutions in the presence of "fluent" speech and phrase length, melodic line, and articulatory agility ratings between 4 and 7 on the BDAE rating scale of speech characteristics. Imitative speech on the BDAE sentence repetition (High Probability subtest) and repetition of the Cookie Theft description evidenced more suprasegmental and segmental errors than spontaneous or elicited speech. Mild language impairments were noted on the BDAE (Goodglass & Kaplan, 1983) and the PICA in auditory comprehension, reading comprehension, and naming. Judged by the criteria listed in other sections, subjects were without accompanying dysarthria or apraxia of speech. AD subjects displayed speech consistent with the perceptual criteria outlined by Darley et al. (1975). Aberrations were noted in the following speech dimensions: precision of vowel and consonant articulation; speaking rate; vocal quality; loudness, pitch, and stress; and resonance. A neurological examination conducted by a board-certified neurologist re-

'This test has psychometric limitations when used for some of the purposes of this project (McNeil, 1989). However, because alternative standardized measures of repetition and complex auditory comprehension were not available at the time of subject testing, it was decided to rely on the BDAE.

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Odell et al.: Perceptual Characteriscs 69

TABLE 1. Location (discrete sites of damage) and degree of damage (Indicated by the numbers) for each subject by group. Subject Group Apraxic Al

A2 A3 A4 Conduction b

Lesion location PRF

PRM

BRO

PRC

POC

0

0

0

0

2

2 0 2

2 1 2

0 2 0

0 1a 0

0 0 0

1 0 0

1 0 1

S-P

S-M

1a

2a

A-G

WER

M-T

INS

2a

2a

la

0 0 0

1

0 0 0

0 0 2

0 0 0

1

1

0

0

la

2a

2a

1

L-N

AIC

GIC

PIC

H-C

THA

0

0

1

0

0

1

0 0 0

0 0 0

0 0 0

0 0 0

0 0 0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

1 0 0

0 0 0

C1

C2

0

0

0

0

0

C3

0

0

0

0

0

C4 0 0 1 2 2 2 2 2 1 1 0 0 0 0 0 0 Dysarthric D1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D2C 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D3 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 D4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Note. PRF = Prefrontal Cortex, PRM = Premotor Cortex, BRO = Broca Area, PRC = Precentral Gyrus, POC = Postcentral Gyrus, S-P = Superior Parietal, S-M = Supramarginal Gyrus, A-G = Angular Gyrus, Wer = Wernicke Area, M-T = Middle Temporal Gyrus, INS = Insula, L-N = Lenticular Nuclei, AIC = Anterior Internal Capsule, GIC = Genu of the Internal Capsule, PIC = Posterior Internal Capsule, H-C = Head of the Caudate, THA = Thalamus. The numbers relate to a scale of severity of involvement such that 0 = no evidence of a lesion, 1 = partial destruction of the region, and 2 = complete destruction of that area. aLesions at these locations were judged to extend deep into the white matter subtending the identified structure. bThis subject refused to submit to a CT scan at the time of testing and, because it was not a part of the selection criteria, the test was not conducted. CAn MRI scan had recently been given this subject and a CT Scan could not be justified; therefore, the judgments were made from these radiologic data instead of the CT scan. vealed signs and symptoms consistent with cerebellar and cerebellar pathway involvement. Judged by the criteria listed above, subjects did not display aphasia or apraxia of speech. Other speech, language, and cognitive tests were also administered to all subjects. These included the Revised Token Test (RTT) (McNeil & Prescott, 1978), the Word Fluency Measure (WFM) (Borkowski, Benton, & Spreen, 1967) and the Coloured Progressive Matrices (CPM) (Raven, 1962). Relevant biographical details and test results for all subjects are summarized in Table 2. A control group of 4 older subjects free of neurological impairments, as determined by performance on the same battery of neurological, speech, language, and cognitive tests, also completed the experimental tasks. Narrow phonetic transcription was completed on the speech of 4 control subjects producing the identical words as the experimental subjects. Two subjects produced one error each, in both cases a distortion. The other subjects displayed no vowel errors. There was no evidence in any subject of the prosodic deviations analyzed in this study. Data Collection Stimuli for this study were the 30 mono-, di-, and trisyllabic words, such as "please-pleasing-pleasingly," that constitute Part II (Words of Increasing Length) of the ABA (Dabul, 1979). Although the sounds in this word list do not constitute a complete inventory of English sounds and are not representative of their frequency of occurrence in the English language, these words were used because they are representative of stimuli that elicit frequent speech errors in neurogenic populations.

For this test administration, subjects repeated each word once after the examiner's live voice model. Speech samples were recorded on high-quality audiotapes using a Marantz stereo cassette tape recorder, model PMD 360, with a Sony microphone. A microphone-to-mouth distance of approximately 10 cm was maintained across subjects to ensure uniform recording conditions. Procedure Perceptual judgments and narrow phonetic transcriptions were performed by two experienced transcribers, one a linguist unfamiliar with disordered speech and the other a speech-language pathologist familiar with neurogenic disorders. Neither transcriber was involved in the initial data collection. Principles of the International Phonetic Association (IPA) (1949) formed the basis for transcription, supplemented by diacritics described in detail by Shriberg and Kent (1982). Consensus transcriptions for each segment and judgments for each prosodic event were developed, following guidelines reported in Shriberg, Kwiatkowski, and Hoffman (1984). Additional utterances, such as entire word or initial sound repetitions and audible struggles to find the appropriate initial or noninitial articulatory position or sound, were noted as events but not phonetically transcribed. No instances of "inadequate responses" (Trost & Canter, 1974), such as semantic paraphasias, failure to respond, or word perservation, occurred in this single-word repetition task. Prosody udgments. Three categories of prosodic deviations were identified and evaluated by the two transcribers (Table 3): abnormalities in syllabic stress, deviations in

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Journal of Speech and Hearing Research

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Odell et al.: Perceptual Characteristics 71

TABLE 3. Summary of the prosodic deviations at the singleword level recognized inthis study. Category Syllabic stress Intraword timing deviations Repeated production difficulties

Deviation Equal stress Abnormal stress Open juncture Long stop closure Initial struggle Noninitial struggle Repetition

intraword temporal parameters, and repeated production difficulties. Stress errors were characterized as either equal or abnormal stress. Equal stress referred to the perception of identical emphasis on both syllables in a disyllabic word or all three syllables in a trisyllabic word, when a difference in emphasis across syllables was expected. Abnormal stress referred to any deviation in the expected relative syllabic weights in two- or three-syllable words. No attempt was made to identify the actual stress relationships that subjects produced in situations in which abnormal stress was noted. In the speech sample of this study, all two-syllable words had the expected syllabic stress relationship of primary stress on the first syllable and no stress (secondary stress) on the second syllable; in trisyllabic words, the expected stress relationship was primary stress on the first syllable, no stress on the second syllable, and secondary stress on the third (e.g., "thickening"). Two kinds of intraword temporal deviations were recognized. The lack of a continuous, sufficiently rapid transition between syllables, resulting in a brief silent interval between syllables, was coded as "open juncture." The lack of smooth, appropriately rapid, and unobtrusive transition from one consonant to another in cases when the adjacent consonants belonged to different syllables (e.g., "pf" in "hopeful"), was termed "long stop closure" (LSC) (Shriberg, 1986). Three types of repeated production difficulties were recognized. An "initial struggle" (IS) referred to an audible effort to produce a sound, cluster, or syllable at the beginning of a word, accompanied by a pause or a change to another sound, which was followed by another attempt at the target. English sounds, non-English sounds, and nonphonemic vocalizations were included in this category. Initial struggles were differentiated from additions at beginning of words by the perception of longer pauses between the initial and the second sound. A "noninitial struggle" (NIS) referred to an added sound, an erroneous but not extra sound, or nonphonemic vocalization that appeared after the initial portion of the word and that was accompanied by any two of the following events: pause, nonphonemic vocalization, sound prolongation, sound repetition, subject verbal apology, or subject failure to continue the production attempt. A superfluous repetition of an entire target word was coded as "repetition." Prosody data analysis. Syllabic stress patterns were judged on the basis of both vowel durational characteristics and other features of syllabic prominence, such as perceived deviations in intensity or pitch. Ability to maintain accurate syllabic stress, intraword temporal features, IS, NIS, and

repetitions were analyzed relative to their occurrence in words with increasing numbers of syllables. Vowel transcription. Both vowels and consonants were transcribed, but because of the volume of data, only vowels are reported in this paper. There were no segments on which agreement could not be reached. Each vowel was analyzed individually in a four-step procedure. Initially, each vowel was coded as accurate or inaccurate. Sounds deviating from the standard American English version, as indicated by Kenyon and Knott (1953), were considered correct ifthey met either or both of two criteria: (a) considered as acceptable allophonic or dialectal variations of the target; or (b) considered within normal variation by the average listener, despite perceptually salient characteristics (e.g., final t] aspiration apparently related to careful speech). Next, omissions or additions of vowels were noted. Each inaccurate vowel production was then coded as a substitution, distortion, or distorted substitution. A substitution was considered a phonetically accurate production of a nontarget vowel. A distortion was considered as an attempt at the target that did not cross the phoneme boundary but that was produced with deviations from the correct production in terms of placement or timing. In addition to lip, tongue, and velar deviations, aberrations of the sound source, such as breathy or murmured productions, were included as distortions (Ladefoged, 1982; Shriberg & Kent, 1982). A distorted substitution was a sound that not only crossed phoneme boundaries but also was a distortion of the substitution, for example, [a:/A]. When there was uncertainty about the nature of the error production, the principle of giving the speaker the "benefit of the doubt" (Shriberg, 1986) was invoked. That is, attempts were made to code an error production as that closest to the target or as a less severe error. For instance, ifthe target was [] and the production could be conceivably transcribed as /i/ or /I/, it was transcribed as //. Finally, the nature of the substitution, distortion, or distorted substitution (application of the diacritics) was determined. Vowel data analysis. Although debate continues over which dimensions are most appropriate to describe articulator positioning for English vowels (Fischer-Jorgensen, 1985; Fox, 1983), traditional descriptors include lip roundedness as well as tongue height, advancement in the oral cavity, retroflexion, and tension (Ladefoged, 1982). In the current study, vowel errors were analyzed according to their appearance in each of these categories. The specific categorization of vowels used in this study is listed in the appendix. In addition, accuracy of vowel production was assessed as a function of increased number of syllables per word and syllabic stress. To discern whether vowels with different characteristics or appearing in different environments were selectively vulnerable to breakdown, both rate and type of vowel error were determined. Error rate was calculated as the percentage of error in each category given the opportunity for each category to occur in the sample. For example, concerning the property of tongue height, error rate on high vowels was calculated by dividing the total number of errors on high vowels by the total number of high vowels in the sample. Error type included the traditional categories used for consonant analysis: substitution, distortion, and omission, as well

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72 Journal of Speech and Heanng Research as distorted substitution. Additions, although coded as errors, were not counted in the error type analysis because extra sounds could not be considered as misarticulations of target sounds. Transcription reliability. The entire speech samples, including both vowel and prosodic production, for all aphasic and dysarthric subjects were retranscribed no less than 6 months after the initial transcriptions; in the AOS group, reliability figures were calculated on the basis of a subset of the speech corpus (17% per individual), a procedure used for a prior study (Odell et al., 1990). Reliability of vowel transcriptions and prosodic judgments for each group was calculated by determining the item-by-item agreement of the consensus transcriptions or judgments on Time 1 (T1) and Time 2 (T2). Shriberg (1972) and Kearns and Simmons (1988) have noted that there is a greater likelihood that interand intrajudge reliability figures will be spuriously high when a large portion of the speech corpus is perceived as correct or incorrect. Following their advice, reliability figures in this study are also reported separately for vowel sounds perceived as accurate and inaccurate. The scoring derived from judgments made during the first transcription. Prosodic judgment reliability was 68% for AOS, 80% for AD, and 90% for CA. The highest number of nonsegmental deviations occurred in the AOS group, followed by the AD and CA groups. Prosodic description is thought to be less reliable than consonant transcription (Shriberg, 1986), possibly because such judgments require comparisons of relative emphasis and timing across several sounds or syllables (Martin, 1972), judgments that may be vulnerable to perceptual adaptation over time. Item-to-item agreement on vowel production in AOS was 97% overall (i.e., on sounds perceived on both T1 and T2 as accurate or as inaccurate). On one occasion there was disagreement on T1 and T2 concerning whether or not an error had occurred. Forty-six percent of the corpus was perceived as in error on T1 and T2; of this total, there was 88% agreement on the nature of the error at the level of narrow phonetic transcription. Item-to-item agreement on the aphasic vowel productions was 96% overall (i.e., on sounds perceived on T1 and T2 as accurate or as inaccurate). On 3% of the corpus, there was disagreement on T1 and T2 concerning whether or not an error had occurred. Seven percent of the vowels were perceived as in error on T1 and T2; of these, there was 86% agreement at the level of narrow phonetic transcription. Regarding dysarthric vowel productions, item-to-item agreement was 85% overall (i.e., on sounds perceived on T1 and T2 as accurate or as inaccurate). On 15% of the corpus, there was disagreement on T1 and T2 concerning whether or not an error had occurred. Nine percent of the vowels were perceived as in error on T1 and T2; of these, there was 45% agreement on the nature of the error (i.e., at the level of narrow phonetic transcription). The major factor contributing to all AD transcription disagreements involved signaling sound source dysfunction (breathy or murmured productions). In 1 AD subject, laryngeal dysfunction was fairly easily associated with vowel production; however, in two other AD subjects, sound source deviations were relatively continuous throughout word production, obscuring the discrete associa-

34

67-80 February 991

tion of laryngeal dysfunction and vowel (or consonant) articulation. Phonetic transcription of vowels is traditionally considered less reliable than that of consonants for various reasons. The continuous nature of vowel articulation perhaps makes transcription more difficult for vowels than consonants. The lack of reliability can be ascribed, in part, to the imperfect ability of any phonetic transcription system, such as the one advocated by the IPA, to represent the flexible nature of vowel articulation. Transcription systems may be too exact to adequately accommodate the somewhat imprecise zonal boundaries in the oral cavity within which vowels are produced. In addition, vowel transcription is difficult because of the naturally occurring variations in vowel quality across speakers. It is difficult to ascertain, especially in disordered speech, whether vowel variation results from differences in dialect or voice quality or from erroneous phonetic production. Data analysis. Because of the small number of subjects and speech tokens, the data were analyzed descriptively rather than through the use of inferential statistics.

Results and Discussion Prosody Stress production. Errors of syllabic stress were initially analyzed disregarding accuracy of vowel production. Totals for equal and abnormal stress were combined for the analysis because of the relatively small number of abnormal stress events (11 instances overall, 8 of which occurred in the AD group). The apraxic group had the highest rate of errors of syllabic stress (43% and 46% for two- and three-syllable words, respectively), followed by the dysarthric (23% and 25%) and then aphasic groups (3%and 5%). Such a close correspondence in error rates between two- and threesyllable words for all groups indicates that mechanisms involved in production of syllabic stress were only marginally affected by an increase in phonetic complexity as gauged by numbers of syllables per word. The rate of stress error, especially abnormal stress, in the dysarthric group is lower than might be predicted from the rather prominent position afforded this attribute by Darley et al. (1975). One factor contributing to the apparent discrepant results may be that Darley and colleagues relied on analysis of contextual speech ("Grandfather Passage"), whereas the current study relied on imitation of single words. It may also be true that the actual rate of stress errors is low and simultaneously perceptually salient; an infrequent and unpredictable appearance of stress errors may well result in a perceptually prominent characteristic (cf. Martin, 1972). Further analysis was undertaken to identify the frequency with which syllabic stress errors were accompanied by vowel misproductions. In the AOS group, 71% of the disyllabic and 74% of the trisyllabic words with stress errors were perceived as having vowel misarticulations. Comparable figures for the AD group were 56% and 50%. Inthe CA group, the incidence of vowel errors in disyllabic words perceived as having stress errors was 3%, and in trisyllabic words, 5%.

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Odell et al.: Perceptual Charactenstics 73

The high coincidence of vowel and stress errors in the AOS and AD groups is not predicted by those who argue that emphasis, as a primarily subglottic aerodynamic phenomenon, should not substantially alter sound production by the upper airway articulators (cf. Kent & Netsell, 1971). Other research, however, suggests that aspects of vowel production other than tongue and lip positioning may indeed be related to syllabic stress. In emphasized syllables the articulators move with greater force, perhaps influencing consonant and vowel overlap in coarticulation (Ohman, cited in Kent & Netsell, 1971; Harrington, 1988). Because errors of syllabic prominence and vowel duration may both result in perceived syllabic stress errors, the primary difficulty in co-occurring vowel and syllabic stress errors is not clear. The root problem may be one of difficulty inproducing appropriate stress, which in turn causes the vowel misarticulation; or it may be that the reverse situation holds, or an unknown independent factor may influence the misproduction of both stress and vowels. Further analyses were completed to investigate the relationship between vowel and syllabic stress errors. Polysyllabic words with stress errors were examined for vowel deviations that might have contributed to the perception of increased emphasis in normally unstressed syllables. Approximately one third of the AOS vowel errors in normally unstressed syllables involved deviations such as inappropriate lengthening of the schwa or other target vowel, or change in the schwa vowel to a more distinct vowel quality such as [i]. Because these vowel dimensions are involved in the perception of emphasis, one may wish to assume a causeeffect relationship. However, increased vowel durations in unstressed syllables and equalized stress patterns may both have been fundamentally dependent on speaking rate. Research has shown that slower speaking rates, more even stress patterns, and increased vowel durations co-occur (Brown, Darley, & Aronson, 1970). Most of the AOS speakers in this study spoke at a slower rate than normal, as evidenced both by perceptual impression of the overall speech samples and by the large number of prolonged consonants and vowels. For 3 AD subjects, vowel misproductions co-occurring with syllabic stress errors typically involved abnormal tongue carriage (e.g., fronted or backed) rather than increased vowel duration. In Subject D4, half of the vowel deviations cooccurring with stress errors involved sound source aberrations (breathy phonation) that intermittently affected portions of words. The apparent unpredictable loss of full phonation in word production seemed to cause this subject to compensate by increasing loudness or pitch, features that are integral cues to emphasis. In cases in which errors of stress were perceived without vowel deviation, abnormal emphasis can be attributed to inaccurate production of the other components of stress, i.e., loudness and fundamental frequency relationships across the syllable chain (Rabiner et al., 1969). Colson (1985) reported relevant data from acoustic analysis of disyllables produced by apraxic speakers. There were no significant differences between disyllables judged as correct or incorrect, with regard to syllabic stress, in duration of the entire utterance or voice intensity. However, a significant difference

emerged in fundamental frequency for the two syllables. Although vowel productions were not individually analyzed, Colson's results provide further evidence that perception of stress errors is not necessarily dependent on the perception of abnormally lengthened vowels. In the CA group, the few vowel errors in the context of syllabic stress errors involved primarily nasalization, a sound deviation not typically related to syllabic stress. Other prosodic features. Nonsegmental speech features other than syllabic stress that contributed to a perception of abnormal prosody included initial (IS) and noninitial struggles (NIS), repetitions (REP), long stop closures (LSC), and open juncture (J). Both LSC and J appear to be features that previous investigators of AOS have referred to either as transitionalization errors (Canter et al., 1985; Square et al., 1982) or syllabic segregation (Kent & Rosenbek, 1982, 1983). The frequency of occurrence of each feature across all groups is summarized in Table 4. The apraxic and aphasic groups produced the same numbers of IS and REP but differed in the frequency of J and NIS. The relative frequency of J errors in the apraxic group supports previous studies noting difficulty in smooth sound-to-sound movements in this group (Canter et al., 1985; Darley et al., 1975; Kent & Rosenbek, 1983; Square et al., 1982). However, it is notable that 11 of the 12 J errors occurred in 1 subject (A4), whereas the other AOS subjects demonstrated little difficulty in this area. In AOS speech, IS errors were more prominent than NIS, consistent with previous reports (Wertz, LaPointe, & Rosenbek, 1984). The conduction aphasic subjects experienced approximately equal IS and NIS errors. The abnormal prosody that is characteristic of AD was not reflected in these features in these single-word targets, as is indicated by the low frequency of occurrence of all categories in the AD group. There was no striking evidence in any individual or group that the frequency of occurrence of IS, NIS, or REP TABLE 4. Summary of frequency of occurrence of word level prosodic features (other than syllabic stress) Ineach group. Measure Subject

IS

NIS

REP

J

LSC

Apraxic Al 5 2 0 0 0 0 0 0 0 0 A2 1 1 2 0 A3 2 A4 2 0 1 11 0 12 1 4 1 Group 9 Aphasic 6 0 6 0 C1 2 0 0 C2 5 1 0 0 0 0 0 0 C3 1 0 0 C4 2 3 Group 9 10 1 6 0 Dysarthric D1 3 1 0 0 0 D2 0 0 0 0 0 D3 0 0 0 1 2 D4 0 0 0 3 0 Group 3 1 0 4 2 Note. IS = initial struggle, NIS = noninitial struggle, REP = repetition, J = open juncture, LSC = long stop closure.

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74 Journal of Speech and Hearing Research

34

was related to number of syllables. These findings for all groups should be generalized with caution, however, because of the small data set.

Overall vowel performance and comparison with consonant production. The percentage of error on vowel production in this single-word repetition task for all subjects in each group is presented in Table 5. The figures for consonant articulation were calculated for a previous study of consonant articulation in AOS (Odell et al., 1990) and for similar forthcoming studies of the other two groups; the percentages were generated by narrow phonetic transcription of the same speech tokens in the same subjects and are included for comparative purposes. As Table 5 shows, the vowel error rate for the AOS group substantially exceeded that for the CA and AD groups. The AOS group misarticulated almost half of all vowels they attempted. The group mean error of 49% also surpasses that of most AOS reports in the literature. Several investigators have reported apraxic group error rates on vowels ranging from 2-16% (Canter et al., 1985; Fry, 1959; LaPointe & Johns, 1975; Lebrun, Buyssens, & Henneaux, 1973; Monoi et al., 1983). Several factors may have influenced the higher vowel error rate in the present study: (1) the use of narrow phonetic transcription, sensitive to subtle production deviations; (2) the coding of vowel prolongation as a segmental error, whereas in other studies it may have been coded only as a prosodic feature; (3) greater severity of the disorder in the current subjects. In the current study, almost one fifth (19%) of all vowels produced by the AD group were perceived as deviations. In describing the speech of their ataxic dysarthric subjects, Darley et al. (1975) reported that vowel deviations were the fourth most prominent perceptual feature, occurring noticeably often but not as frequently as consonant errors. Unfortunately, the Darley study did not report data on absolute

TABLE 5. Summary of individual and group error rates on vowels and consonants. Vowels

Apraxic Al A2 A3 A4 Group Aphasic C1 C2 C3 C4 Group Dysarthric D1 D2 D3 D4 Group

February 1991

frequency, and the general paucity of detailed accounts of vowel articulation in AD hinders a more comprehensive comparison of results of the current study. In comparison to both the AD and AOS groups in this study, vowel production by the aphasic group was less in error, with a mean vowel error rate of 8%. Among the few studies reviewing vowel articulation in CA, only Monoi et al. (1983) report actual frequency data. Approximately half of all vowels produced by their subjects were in error, a rate substantially exceeding that for aphasic subjects in the current study. The findings of the current study differ from previous studies regarding overall vowel error rate in the three groups. Vowel error rates were higher in the AOS group than the literature predicted and lower inthe CA group than previously reported. Whether the discrepancies reflect differences in overall severity of the disorder, transcription method, speech stimuli, or transcribers cannot be fully determined from these data. In the current study there was little absolute difference in any group between error rates on vowels and consonants (Table 5). Percentage of error on vowels slightly exceeded that for consonants in both the AOS and AD groups, with the reverse trend inthe CA group. Previous reports of group data indicate that consonants were misarticulated more often than vowels in single-word utterances in AOS (Canter et al., 1985; LaPointe & Johns, 1975; Monoi et al., 1983; Trost & Canter, 1974), in conduction aphasia (Monoi et al., 1983), and in contextual speech in ataxic dysarthria (Darley et al., 1975). In contrast, the opposite pattern was reported by Lebrun et al. (1973) for one of their apraxic subjects, who misarticulated a slightly higher percentage of vowels than consonants. Arguments exist to support either similar or differential vowel and consonant error rates. Earlier studies, excepting Canter et al. (1985) and Trost and Canter (1974), relied on broad phonetic transcription, a procedure that may have obscured the frequency of subtle vowel errors. Previous investigators sug-

Vowel Production

Group

67-80

Consonants

No.

No. errors

%errors

No.

No. errors

%errors

56 58 58 58 230

50 3 24 35 112

89 5 41 60 49

101 108 106 104 414

77 10 39 66 192

76a 10a 37a 63a 46a

57 58 52 58 225

6 0 2 8 16

11 0 4 14 7

102 106 88 106 402

20 13 14 18 65

20 12 16 17 16

58 58 58 58 232

16 2 10 15 43

28 3 17 26 19

106 106 106 105 423

13 5 30 21 69

12 5 28 20 16

aData derived from Odell et al., 1990.

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Odell et al.: PerceptualCharacteristics 75

gested that vowels and consonants involve different motor programs (Fowler, Rubin, Remez, & Turvey, 1980; Ohman, 1966,1967; Perkell, 1969; Ryalls, 1987), perhaps resulting in differential error rates. It is possible that utterances longer than those required in this study would yield a different error pattern. However, the similarity in vowel and consonant error rates for each group in this study is interpreted as evidence against selective impairment of either speech sound category. Considerable intersubject variation in the degree of vowel (and consonant) accuracy was evident in each group, especially the apraxic group. One AOS subject produced most vowels correctly, whereas the other 3 had substantial numbers of errors. Trost and Canter (1974) noted a similar trend intheir subjects with Broca aphasia and AOS. Until additional data are collected, our understanding of such variability is necessarily limited. Perhaps the intersubject variation in production accuracy corresponds to severity of the speech disorder: The more severe the disorder, the greater the disruption of both vowels and consonants (cf. Trost & Canter, 1974). Types of vowel errors. As Table 6 shows, distortions were the predominate type of vowel error for the AOS and AD groups, constituting, respectively, 65% and 81% of the total errors in each group. In contrast, distortions constituted only 24% of CA vowel misarticulations; for the CA group, substitutions were the primary error type, accounting for 65% of errors. Because of the primacy of vowel distortions in two groups and the limited data available in the literature on the nature of sound errors, further analyses were conducted. For the 3 apraxic speakers producing vowel distortions, abnormal sound prolongation was the most common type of deviation; for the group as a whole, prolongations constituted 74% of all distortions, followed by inappropriate raising, lowering, fronting, or backing of the tongue body. In contrast, for the dysarthric subjects, distortions seldom involved inappropri-

ately increased durations and, instead, typically involved abnormal tongue positioning and sound source aberrations. Although vowel distortions have been described as a characteristic of apraxic dysarthria (Darley et al., 1975), they have not been commonly associated with AOS. However, emerging evidence from perceptual (Odell et al., 1990; Square et al., 1982), acoustic (Duffy & Gawle, 1984; Kent & Rosenbek, 1983; Ryalls, 1981, 1986), and physiologic (Itoh & Sasanuma, 1984) studies suggests that many vowel errors coded as substitutions may in fact be distortions. Such a generalization is consistent with results of the current study. Because of the absence of relevant vowel analyses in CA, expectations about articulatory proficiency were sought from consonant studies in CA. There are conflicting reports in the literature on the precision of consonant articulation. Some perceptual (Goodglass & Kaplan, 1983; Monoi et al., 1983) and acoustic studies (Shewan, Leeper, & Booth, 1984) indicate CA subjects are more likely to produce well-articulated sound substitutions than distortions, a trend consistent with the results of this vowel study. To reveal patterns of error produced in vowel substitutions or distorted substitutions, a series of substitution matrices were developed. These matrices, one for each group, are shown together in Figure 1. Vowels listed along the Y axis are targets, those along the top X axis are vowels substituted for the targets. As the figure illustrates, predictable patterns of vowel replacement were not apparent in any group. Substitutions and distorted substitutions in the AOS speakers were the most numerous of all groups and provide the best opportunity to discover patterns. In these speakers, more front and middle vowels were involved in replacements than back vowels. There was a tendency for front vowels to replace each other and back vowels to replace each other; centralized vowels (/al) were usually but not always replaced by vowels at the extremes of the vowel quadrilateral (/h/ and /a/).

TABLE 6. Distribution of vowel error types (numbers and percentages) for Individuals and groups.

Subjects Apraxic Al A2 A3 A4 Group Aphasic Cl C2 C3 C4 Group Dysarthric D1 D2 D3 D4 Group

Total

Substitutions

Distorted substitutions

Distortions

Omissions

Additions

errors

#

%

#

%

#

%

50 2 24 37 113

0 0 3 8 11

13 22 10

8 2 2 18 30

16 100 8 49 27

42 0 19 11 72

84 79 30 64

0 0 0 0 0

-

3 0 6 3 12

6 20 8 10

7 0 2 8 17

5 0 1 5 11

71 50 63 65

0

1 0 0 3 4

14

0 0 0

-

38 24

1 0 1 0 2

14 50 12

4 1 0 0 5

36 100 23

16 2 9 16 43

2 1 1 0 4

12 50 11 9

3 0 1 0 4

19 11 9

11 1 7 16 35

69 50 78 94 81

0 0 0 1 1

6 2

0 0 0 0 0

-

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#

%%

76 Journal of Speech and Hearing Research

34 67-80 February 991

Substitution i

I

e

£

ae

a

Q

3

U

U

4

4

100-

I

4

DI.

90-

M;High = Mid EL Low

4 "r

80C

I

70 -

I

o

60-

"

50-

o

40-

L

30-

1_

U

10 0-

Substitution Matrix plain digit

0

= AOS = CA = AD

number = absolute frequency FIGURE 1. Matrix displaying the frequency of occurrence of vowel substitutions ineach group. Target segments are listed along the Y axis. Segments that were substituted for the targets are listed along the upper frame of the X axis. Of the monophthong vowel errors produced by the AD group, 50% were replaced by diphthongs. A related phenomenon was noted by Kent & Rosenbek (1983), who pointed out that vowel substitutions in AD not infrequently appear on spectrograms as involving deviant movement patterns that are not characteristic of simple sound substitutions. Tongue and lip positioningeffects. A series of analyses was conducted to investigate the relationship between articulatory parameters (e.g., tongue height) and vowel errors in the three groups. There was considerable intersubject variation in degree of error in all categories of analysis, especially in the AOS group. As Figure 2 shows, error rates in all three groups were greatest on the low vowels (l and /la). All AOS subjects showed this pattern, although only one subject in the CA and AD groups did. Vowel errors relative to the dimension of tongue advancement are shown in Figure 3. The AOS group produced over 20% more errors on back vowels (/lu, /o/, I//, /a/) than front vowels (/i/, hi, /Ic/, I/i) Differences among vowel types were not striking in the CA or AD groups. Tense vowels (ii, I/a, /o/, and //) exhibited more errors than lax vowels in all groups. However, in all groups, these vowel categories were almost equally vulnerable to disruption. The error rate on tense and lax vowels was 49% and 47%, respectively, for the AOS group, 13% and 6%, respectively, for the CA group, and 23% and 17%, respectively, for the AD subjects. The tendency to err on tense vowels was

or

20-

31

0

1

.

1,

I I

11 1 KIM

{I

I ....

CA

AOS

AD

FIGURE 2. Means and ranges of error rates on vowels categorized by the dimension of tongue height for each group (AOS = apraxia of speech, CA = conduction aphasia, AD = ataxic dysarthria). Digits above the range bars Indicate the number of subjects demonstrating errors of that type. rather strong, as 3 of the 4 CA subjects and all the AOS and AD subjects contributed to this trend. Analysis revealed that, in the aphasic and dysarthric groups, error rate was slightly higher on nonretroflexed than retroflexed vowels (19% vs. 6% in the CA subjects and 8% 4

10090-

ES Front vowels [Z Middle vowels 7Z- Back vowels

44 I'

8070-

.

4

6o 60 5040-

L

I

I I I I I I

1 4

30 300

20100-

35

Ig

2i I

L LI

AOS

11

11

CA

1

ims ..... 1

^

AD

FIGURE 3. Means and ranges of error rates on vowels categorized by the dimension of tongue advancement for each group (AOS = apraxia of speech, CA = conduction aphasia, AD = ataxic dysarthria). Digits above the range bars indicate the number of subjects demonstrating errors of that type.

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Odell et al.: Perceptual Characteristics 77

vs. 0% in the AD subjects). In the apraxic group, the error rate was approximately equal in both categories (50% vs. 47% for retroflexed and nonretroflexed, respectively). Nonrounded vowels were more in error than rounded vowels for the aphasic and dysarthric groups (9%vs. 2% in the CA group and 19% vs. 16% in the AD group). For the AOS group, rounded vowels were more in error (55% vs. 46%). However, the absolute difference in rate of error on these two vowel categories was too small to assume any reliable difference in each group. The tendency of these subjects to misarticulate more often on low, front, tense, and nonrounded vowels is perhaps related to the lower frequency of occurrence of many vowels in these categories (Carterette & Jones, 1974). Another potential explanation for this error pattern derives from Stevens' (1971) acoustic studies. He suggested that certain isolated vowels might be selectively easier to articulate in such a way that they are perceived as accurate, because they are produced in an apparent "preferred range" in the continuum of articulatory configuration of the oral tract; in these preferred ranges, or quantal zones, even large changes in oral tract configuration result in relatively limited alterations in acoustic properties of the signal. Conversely, isolated vowels produced in nonquantal zones may be more difficult to articulate accurately, because minor modifications in tongue position or other articulatory parameters in these zones result in large changes in the acoustic attributes of sounds. Vowels produced in quantal zones were identified by Stevens as /a/, /i/ and /u/. Of these, only /a/l and /i/ were included in the speech sample in the current study. Data from these subjects do not strongly support Stevens' hypotheses. Table 7 presents error rates for vowels in the quantal zones, vowels in zones adjacent to quantal zones, and vowels in areas relatively distant from the quantal zones. TABLE 7. Percentage of vowel errors categorized according to place of articulation Inthe "quantal" or other zones of the vocal tract: Group data. Group Vocal tract area Quantal zone /a/ /i/ M Adjacent to quantal zone in vowel quadrilateral h/1 /o/ /3/

M Nonadjacent to quantal zone invowel quadrilateral /E/ /a/

AOS

CA

AD

73 33 53

25 15 20

33 25 29

34 75 50 67 57

4 0 8 0 3

14 50 8 67 35

75 0 8 56 15 15 50 0 6 /o/ 50 0 25 M 58 4 14 Note. Each figure represents percentage of error relative to total sounds in that vowel category. AOS = apraxic, CA = conduction aphasic, AD = ataxic dysarthric.

All groups produced vowels in quantal zones about as proficiently as or less proficiently than vowels in adjacent or distant oral tract zones. Possibly, predictions for errors based on zones are appropriate only for vowels produced in isolation, as Stevens examined. Consonant articulation effects. Several investigators have raised the notion that the interdependency of articulation between vowels and consonants is a factor in vowel production errors. Trost and Canter (1974) reported that the majority of vowel misarticulations produced by their Broca aphasic subjects (presumably with AOS) occurred in association with adjacent consonant errors. These authors proposed that difficulties in either consonant selection or consonant-vowel (CV) articulatory transitions were the core abnormalities affecting misarticulations of vowels. In a related argument, Kent and Netsell (1974) suggested that failure to make the vocal tract constriction for consonants may result in the prolongation, even diphthongization, of vowels adjacent to the target consonants. Various investigators have presented acoustic (Kent & McNeil, 1987; Ziegler & von Cramon, 1986) and perceptual (Ziegler & von Cramon, 1985) evidence that CV transitions are involved in vowel errors in AOS. This CV relationship has not been examined perceptually in the other groups. In the current study, all groups produced instances of vowel errors in the context of adjacent consonant errors. In the apraxic group, 93% of all vowel misarticulations occurred in association with an adjacent consonant error. In the dysarthric group, the corresponding figure was 63%, and in the aphasic group, an intermediate 81%. The relatively high incidence of paired vowel-consonant errors in AOS and AD implicates the complexities of CV articulation in vowel errors in these subjects. The fact that paired CV errors occurred in both groups does not necessarily imply the same cause in each group. As several investigators have pointed out, motoric impairment is traditionally suspect in AOS (e.g., Rosenbek, Kent, & LaPointe, 1984) and AD (Darley et al., 1975), whereas linguistic breakdown in phoneme selection has been considered in such breakdowns in CA production (e.g., Goodglass & Kaplan, 1983). In the AD group, the lower incidence of vowel errors produced in the context of consonant misarticulations strengthens the notion that the complexities of vowel articulation themselves contribute heavily to vowel disruption. For instance, steady maintenance of tongue and lip positions may have been equally as influential in vowel breakdown as the effects of consonant production. Such a notion is consistent with a proposal by Kent and Netsell (1971) that impairment in articulator movement may not be the basic abnormality inAD. Recent findings in AD subjects of poor control of isometric force and static position (McNeil, Weismer, Adams, & Mulligan, 1990) also support this idea. Word position effects. Both apraxic and dysarthric subjects in this study exhibited inaccurate vowel production more often in initial position than in noninitial loci in words. Percentage of error was 59% and 38% for initial and noninitial positions, respectively, for the AOS group; corresponding figures were 25% and 11% for the AD group. The reverse trend was noted in the CA subjects (4% and 12% error in

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78 Journalof Speech and HearingResearch

34

initial and noninitial positions, respectively). As this pattern was evident in both two- and three-syllable words in each group, figures for both word types were combined to form the final percentages. Individual patterns of vowel breakdown did not always correspond to the group trend. These results are in general agreement with trends noted in previous studies concerning locus of general articulatory difficulty, not necessarily tied to vowel production. Yorkston and Beukelman (1979) reported that their single conduction aphasic subject made substantially more articulatory errors (as indicated by the need to self-correct) in final position of words than other positions. In AOS, there is conflicting evidence concerning the selective vulnerability of initial position in consonant articulation: A preponderance of errors in initial position of words has been reported by some investigators (Canter et al., 1985; Johns & Darley, 1970; Shankweiler & Harris, 1966) but not others (Dunlop & Marquardt, 1977; LaPointe & Johns, 1975; Odell et al., 1990). Comparable analyses on AD subjects have not been published, but there has been no tendency noted for more errors to occur in one or another position of words. Effects of numbers of syllables. For the apraxic and dysarthric groups, vowel error rate was slightly higher in monosyllabic than in polysyllabic words, as is shown in Figure 4. The aphasic group exhibited a higher error rate in polysyllabic words. However, differences in error percentages across words of differing numbers of syllables were minimal for all groups. Because the literature includes no vowel data with which to compare these findings, reports of consonant production were examined to provide a framework for interpretation. These studies provide some support for the present results.

10090 -

4 [M Monosyllabic =] Disyllabic 177Trisyllabic

44 I

T

80 7060

®

50-

o_

40-

3

30 3

20 -

1

10 0-

I

AOS

I

-",

~

1

CA

AD

... F.

......

FIGURE 4. Means and ranges of error rates for each group (AOS = apraxia of speech, CA = conduction aphasia, AD = ataxic

dysarthria) on vowels according to their appearance in monosyllabic, disyllabic, or trisyllabic words. Digits above the range bars Indicate the number of subjects demonstrating vowel errors ineach word type.

67-80 February 991

In AOS (as well as Broca aphasia with presumed AOS), investigators report evidence that error rate does not change systematically as words increase in number of syllables (Johns & Darley, 1970; Mlcoch, Darley, & Noll, 1982; Odell et al., 1990), although opposing viewpoints have also been described (Shankweiler & Harris, 1966). Further support for results of the present study comes from a report by NespouIous, Joanette, Ska, Caplan, and Lecours (1987), who found that their Broca aphasic subjects misarticulated more consonants in monosyllabic than polysyllabic words, whereas conduction aphasic subjects erred more in the polysyllabic words.

Summary This study has presented detailed perceptual analyses of word-level productions that suggest that prosodic features and vowel productions contribute to effective differentiation among AOS, CA, and AD subjects. Before reviewing specific group production trends, it is worth noting the key results that characterized all groups. Within each group, vowel and consonant error rates were comparable. This atypical finding suggests that these two categories of sounds were equally vulnerable to phonetic disruption in this single-word task. Further, an increase in number of syllables in a word did not increase the vowel error rate, per number of vowels, for any group. Particular aspects of vowel production analyzed in this study associated AD and AOS, albeit rather weakly, while dissociating CA. Vowel performance patterns that were similar in AOS and AD include predominant errors in low, tense, and back vowels; primacy of distorted rather than substituted vowels; higher percentage of error in initial than noninitial positions in words; larger percentage of vowel errors in monosyllabic than polysyllabic words; and higher error rate in syllables that are normally stressed. The CA group differed from the other groups in several ways: a preponderance of vowel substitutions over distortions; higher percentage of errors in polysyllabic than monosyllabic words; and larger percentage of vowel errors in final rather than initial position of words. These specific intergroup differences, however, were often small and must be confirmed by replication of these speech tasks in studies using additional subjects. The prosodic features analyzed in this investigation also revealed intergroup differences. Almost half of the polysyllabic word productions by the apraxic speakers displayed syllabic stress errors, whereas only one quarter of the dysarthric productions included stress abnormalities. Stress errors were negligible in the aphasic subjects. The apraxic and dysarthric subjects were similar in demonstrating more difficulties initiating speech production than in continuing a word once it had been begun, a pattern also found in vowel errors. Differences in locus of prosodic breakdown did not characterize the aphasic group; difficulties in initial and noninitial positions of words were similar in frequency of occurrence. Sound transitions, as reflected in open juncture, posed substantial articulatory obstacles for some AOS subjects, less difficulty for the AD subjects, and virtually no problem for aphasic subjects.

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Odell et al.: PerceptualCharacteristics 79

This study has presented a complex array of findings, some of which are consistent with traditional perspectives on these three neurogenic disorders and others of which contrast with the characteristic descriptions. Performance of individual subjects in each group did not always correspond to group patterns, perhaps because of such factors as severity of the disorder, degree of compensation for the disorder, nature of the disorder, or sampling error of the study. Further research, utilizing additional subjects and relying on other speech tasks, is necessary to verify trends noted in this study and to corroborate perceptual findings with acoustic and physiologic data now available in the literature.

Acknowledgments This research is supported by NINCDS Grant No. N518797 and NINCDS Core Grant No. 5030 HD03352. We wish to express our appreciation to Jeffrey Metter, M.D., for reading the CT scans and to Claudia Blair and Gary Weismer for assistance with various aspects of the study. We also express our appreciation to Milly Boyer for her help in manuscript preparation. A portion of the data in this manuscript was presented at the 1989 Clinical Aphasiology Conference, Lake Tahoe, NM.

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Received October 9, 1989 Accepted April 5, 1990 Requests for reprints should be addressed to Katharine Odell or Malcolm R. McNeil, Ph.D., Department of Communicative Disorders, University of Wisconsin-Madison, Madison, WI 53706.

Appendix The IPA classification system, discussed in detail by Shriberg and Kent (1982), was followed in this study. Speech stimuli used in this study incorporated 10 of the 14 monophthong vowels in American English and none of the diphthong vowels. Tongue height: high: /i/, /1/, /u/ mid: /a/, la/, /o/, /c/,/o/ low: //i, /a/

Tongue advancement: front: /i/, /i/, /c/, /E/ mid: /a/, /a

back: l/u/, /lo/, /, /a/ Tenseness: tense: ii, /a/, /3/, /o/ lax: /i/, / , l, /u/, //, la,/ Retroflexion: retroflexed: I/aI nonretroflexed: all other vowels included in the study Rounding: rounded; /u/, /o/, /o/, la unrounded: /i/, /i/, /I, /i/, /a/, I/a

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