Phonetic analysis of a case of foreign accent syndrome

Journal of Phonetics (1992) 20, 457-474

Phonetic analysis of a case of foreign accent syndrome John C. L. Ingram Department of English, University of Queensland, St Lucia Q. 4072, Australia

Paul F. McCormack and Meredith Kennedy Department of Speech and Hearing, University of Queensland, St Lucia Q. 4072, Australia Received 21st June 1990, and in revised form 121h March 1992

Analysis of a case of Foreign Accent Syndrome (F AS) is undertaken to determine the phonetic features which contribute to the perception of foreign accent and to identify the nature of the underlying speech disorder. A phonetic process analysis of pre-trauma and post-trauma speech samples provides predictor variables for a multiple regression analysis of "foreign accent" ratings . Hypotheses of a disorder of timing and/or an altered vocal tract setting in FAS are evaluated.

1. Introduction This paper adds to a small but growing collection of case studies of a rare neurological speech disorder known as Foreign Accent Syndrome (FAS). Unlike previously published accounts, a sample of th~ subject's speech had been adventitiously recorded prior to her illness and was available for comparison with her post-trauma speech. FAS is distinguished from the dysarthrias or speech apraxia in that the predominant impression of listeners is one of "foreignness" rather than speech disorder or phonetic disintegration. Significantly, listeners do not agree about the identity of the "foreign accent", but are quite clear as to its "foreign" quality. The speaker in the current study was variously judged to sound "Asian" , "Swedish", or "German" . Abnormal prosodic features play a prominent role in all published accounts of FAS. Articulation errors and paraphasias are typically reported to be mild or occasional, as they were also in the present case. FAS speakers are aware of and often embarrassed by their altered speech. FAS usually arises as a result of a cerebro-vascular accident (CVA, or stroke) and aphasis of predominantly anterior symptomatology, as in the present case. There is a suggestion that FAS, in a clinically less prominent form, may be a more frequent accompaniment of Broca's Aphasia and Agrammatism (Ardila, Rosselli & Ardila, 1988; Miceli & Caramazza, 1988). A precise phonetic characterizat!on of FAS is of interest not only from the viewpoint of more accurate differential diagnosis, but also for understanding the production mechanisms which may underlie the disorder. The study of F AS is also of general interest for the light that it may throw on phonetic features which cause the perception of foreign accent in normal speech. A 0095-4470/92/040457 + 18 $08.00/0

© 1992 Academic Press

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major goal of the present study was to attempt to determine the relative salience of different phonetic features, segmental and suprasegmental, contributing to the perception of foreignness in the patient's speech. The results of the study have implications for phonetic mechanisms underlying accentual colouring of speech m general. 1.1. Phonetic characteristics of FAS speech

Anomalies of stress, rhythm and intonation are frequently reported in FAS, through not all reported prosodic features are consistent with one another. Foreign sounding intonation is usually noted, which Blumstein, Alexander, Ryalls, Katz & Dworetzky (1987), on the basis of acoustic observations, related to "sharply rising" terminal contours at the ends of phrases and sentences , a feature previously reported by Monrad-Krohn (1947). On the other hand , Graff-Radford, Cooper, Colsher & Damasio (1986) reported reduced peak to valley fundamental frequency ranges and a general reduction of prosodic contrasts for their subject. Graff-Radford et al. reported excessive pausing at phrase boundaries and "unnecessary" pausing elsewhere in utterances. Non-native stress and rhythm patterns were also noted by Whitaker (1982); Blumstein et al. (1987); Ardila et al. (1988). Several contributory features to these abnormalities of stress and rhythm have been noted: a tendency towards non-reduction of unstressed vowels, occasional misplacement of lexical stress, a tendency towards "syllable timing", away from the customary "stress timed" pattern of English, occasional resyllabification and difficulties with syllable transitions . A staccato speech rhythm is often reported, together with the impression of a tense articulatory setting. The segmental features that distinguish F AS from other kinds of speech disorder seem to be related to, or may be derivative of suprasegmental disorders, as Blumstein et al. suggest. Unlike many dysarthrias in which slurring and weakening of consonantal gestures consistent with articularory undershoot is found, there appears to be selective strengthening of some consonants, lending an "explosive character" (Miceli & Caramazza, 1988) to FAS articulation . Blumstein et al. (1987) observed a reduced incidence of expected lenition processes, in terms of a failure of alveolar stops to weaken to flaps in post-tonic intervocalic environments. Vowel _feature changes are reported to be more prominent than consonantal changes. Perceived vowel quality shifts generally appear to be in the direction of strengthening: movement towards a more peripheral position, vowel lengthening, (Graff-Radford et al. , 1986), "colouring" of /'d/ (Whitaker, 1982; Blumstein et al. , 1987; Gurd, Bessell, Bladon & Bamford , 1988). However , vowel weakening processes are also suggested by observations of occasional monophthongisation of diphthongs (Whitaker, 1982), and vowel shortening (Pick, 1919). Acoustic analysis of vowel quality in word-list reading by an FAS subject (Blumstein et al., 1987), showed only slight divergences from normal expectations for duration and formant frequencies. Slightly lower F 1 values suggested a more closed articulatory setting. There was also greater token variability in formant measurements, comparable to that observed in other aphasics (Ryalls, 1986). The foregoing, not entirely consistent, pattern of reported phonetic characteristics of FAS speech, suggests the need for further close phonetic observation, both impressionistic and instrumental. There is also a need to determine the relative

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contribution of various phonetic features mentioned above to the perception of F AS speech. In addition to these descriptive tasks, there remains the problem of explaining the speech mechanism(s) underlying FAS. Blumstein et a!. hypothesize that a disorder of prosody-of timing and rhythm control in particular--can account for both the prosodic and segmental abnormalities observed in F AS . Segmental featural disturbances such as vowel epenthesis, changes to syllable structure, suppression of vowel reduction and strengthening of flaps in FAS are seen as secondary consequences of a primary disorder of speech timing. To account for the dominant perceptual impression of "foreignness" rather than "disorder", Blumstein et a!. submit that the abnormal phonetic processes observed in F AS speech represent possible phonological processes attested in at least some of the world's languages . This corollary hypothesis is endorsed by Gurd et a!. (1988), who take the additional step of identifying occurrences of phonetic processes in their patient's speech with phonological processes of particular languages. This pattern contrasts with dysarthric speech in general, or phonetic disintegration found in dysfluent aphasia, where the phonetic alterations could not be said to represent normal phonological processes of actual languages. An alternative to Blumstein et a!. 's timing control hypothesis, suggested by Graff-Radford et al. (1986), is that FAS involves "a tense speech posture" arising from increased muscle tone and/ or altered long-term vocal tract postural settings during speech production. An altered vocal tract postural setting could affect both long-term characteristics of voice quality (in the broad sense used by Laver, 1980) and short-term, segmental features. Different vocal tract settings have been implicated in phonetic differences among regional and social dialects as well as across languages (Nolan, 1983; Esling, 1987). What is needed to resolve the questions of whether F AS speech involves disturbances of speech timing, postural setting, or some other mechanism, and whether or not the phonetic transformations that characterize F AS speech represent intrusions of possible or actual phonological processes, are close phonetic observations of FAS speech, with an eye to connected speech processes in normal speakers. 2. Subject and speech materials The subject (OS) was a 56-year-old Brisbane-born woman who was left with a stable and unmistakable F AS following a CV A some 18 months prior to gathering the post-trauma speech samples used in the present study. Immediately after her stroke, the subject was acutely aphasic, with symptoms of speech apraxia, or difficulties in initiating speech gestures. A CT scan indicated a well-defined subcortical haematoma centred on the lentiform nucleus. The aphasic symptoms progressively cleared, leaving her after 12 months with speech that had a marked foreign accent quality, with occasional paraphasias and dysfluencies. A tape recording of her speech made some 12 months prior to her CV A was available, from which it can be judged that she spoke with a typical, fairly broad, Australian accent. The pre-trauma speech sample consisted of an interview, recorded on a home cassette recorder, between OS and a fortune teller who was conducting a card reading. The quality of the recording was adequate for impressionistic auditory analysis and for obtaining perceptual ratings, but largely unusable for acoustic analysis, due to a poor signal-to-noise ratio. OS spoke little

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during the session, largely responding with one word replies to questions put to her by the fortune teller. However, 15 multi-word utterances by DS, which constitute the "pre-trauma utterance set" , were extracted from the interview for detailed phonetic analysis and perceptual rating. Extensive recordings of DS's speech were taken between 13 and 15 months post-trauma. Apart from the FAS colouring, her speech at this stage was quite fluent and intelligible, with only occasional paraphasic errors. It was noted that FAS symptoms were more prominent in spontaneous conversation than in automatic speech or sentence repetition. Two short passages of connected speech, consisting of "talk about your family" and "the cookie theft", a picture-story elicitation, provided 15 sentences for a "post-trauma utterance set". All utterances consisted of prosodically unified phrase or tone groups. Indeed, prominent phrase group boundaries, clearly marked by pauses, were a notable feature of DS's post-trauma speech.

3. Overview: aims and methods of analysis

Although the diagnosis of F AS was clearly indicated from the case history and neurological and speech pathology reports, it was necessary to confirm that the dominant perceptual impression of the subject's speech was one of "foreign accent" over that of "speech disorder". Therefore, a perceptual rating experiment was first undertaken on the pre- and post-trauma sets of utterances. This is described in Section 4 below. The expected pattern of substantially raised "foreignness" ratings across the pre- and post-trauma utterance sets was confirmed. These ratings also served to construct a dependent variable that was used in a multiple regression analysis intended to identify the major phonetic features contributing to the perception of foreign accent. An auditory phonetic analysis of the pre- and post-trauma. utterance sets is reported in Section 5. A broad phonetic/phonemic transcription w.as made of each utterance, using a waveform annotation program (Jordan, 1988). Then, two of the authors (JI and PM) independently annotated the transcriptions with phonetic process labels, intended to capture the phonetic features necessary to map the phonemic transcriptions into narrow phonetic transcriptions of the subject's utterances. The system of phonetic process labels that was used had been originally developed for a study of connected speech processes in normal speakers and was supplemented with additional labels for the present study (summarized in the following section (Table 1). The distribution of phonetic processes in the subject's pre- and post-trauma utterance sets were then compared with each other and with data obtained from a study of connected speech processes in Australian English (Ingram, 1989), in an effort (a) to establish the character of the phonetic changes that had taken place in the subject's speech and (b) to evaluate them with respect to lenition and reduction processes found in normal connected speech in the subject's native language and regional accent type. The phonetic process labelling also provided the independent variables for the multiple regression analysis of perceptual correlates of foreign accent ratings which is reported in Section 6.

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4. Perceptual rating experiment Although the clinical indications were that DS presented a classic case of FAS, it was necessary to confirm the dominant perceptual impression of "foreign accent" over that of "speech disorder". At the same time, it was hoped that there would be sufficient variability in the foreign accent ratings among the pre- and post-trauma utterances to permit construction of an effective dependent variable to assess the perceptual salience of particular phonetic features. 4.1. Method and procedures Thirty final-year speech therapy students from the University of Queensland rated the 30 pre- and post-trauma utterances on scales of Foreign Accent, Speech Disorder and Intelligibility (see Table Ia for rating scales). The students all had some clinical training in assessing speech disorders, though none appeared to be familiar with the phenomenon of FAS. Utterances were presented over a loudspeaker in partial-random order (no more than two pre- or post-trauma utterances in succession) and ratings were made with the benefit of a typed transcript to avoid possible target misidentifications. Each utterance was presented three times with an inter-token interval of approximately 2 s and an inter-trial interval of 5 s. Raters were not informed of the purpose of the experiment or given any clues as to the number or characteristics of the speakers. Debriefing after the experiment indicated that all believed there was more than one speaker represented. None of the students appeared to be familiar with the phenomenon of FAS.

4. 2. Results A mean rating score was calculated for each utterance across the 30 raters for each of the three measures of Foreign Accent, Speech Disorder and Intelligibility. A split-half reliability test, in which mean scores calculated on the basis of half the sample were correlated with scores obtained from the other half of the sample, indicated that the mean rating scores were highly stable (r > 0. 90 for all scales). The mean scores for utterances in the pre- and post-trauma utterance sets were then compared, using separate one-way ANOVAS for each of the three scales. The results are shown in Table lb. For the Foreign Accent scale, the scores for the pre- and post-trauma utterance sets barely overlapped and the mean differences were highly significant (p < 0.0001), with the post-trauma mean (2.51) falling between "slight" and "moderate" ratings on the four"point scale. For the Speech Disorder scale, there was merely a trend (p < 0.08) towards a mean difference, with the post-trauma utterance mean (1.50) falling between the ratings of "normal" and "questionable" on a three-point scale. There was no difference between the pre- and post-trauma sets on the mean Intelligibility scores. Intelligibility scores reflect the combined effects of tape recording quality and the inherent intelligibility of the speaker. These two factors were working against each other in the comparison of pre- and post-trauma utterance sets and hence the interpretation of the Intelligibility scores is problematic.

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TABLE I. (a) Foreign accent syndrome rating scales Foreign Accentedness 1 Australian .English, no trace of foreign accent 2 Slight or possible trace of foreign accent 3 Moderate or fairly definite trace of foreign accent 4 Strong foreign accent, definitely not Australian English Intelligibility 3 High intelligibility, unmistakable what is being said 2 Moderate intelligibility. Some words hard to understand, but not hard to understand general message 1 Low intelligibility. Message easily mistaken, hard to understand Speech Disorder 1 Normal. No speech errors 2 Questionable. One or two detectable speech errors 3 Disordered . Two or more speech errors (b) Mean ratings and results .of one-way ANOV AS on scales of Foreign Accent, Intelligibility and Speech Disorder for pre- and post-trauma utterance sets Group means Analysis Foreign Accent Intelligibility Speech Disorder

Pre-trauma

Post-trauma

F ratio

Probability

1.39 2.32 1.24

2.51 2.57 1.50

39.15 2.17 3.27

0.0000 0.1512 0.0810

In summary, the expected pattern was confirmed; there were significantly elevated scores of "foreign accent", but only marginally elevated "speech disorder" ratings for the post-trauma utterance set in relation to the pre-trauma set. Also, there appeared to be sufficient spread of FA scores on individual utterances, even within the post-trauma set, to warrant use of this measure as a dependent variable in the search for phonetic correlates of foreign accent. 5. Phonetic process analysis Impressionistically, the pre- and post-trauma speech characteristics were markedly different. A detailed phonetic process analysis was undertaken in order to characterize these differences more precisely and, at the same time, to compare phonetic processes in F AS speech with normal connected speech processes in the speaker's native dialect (Brisbane English). The reference data base for these comparisons was a phonemically transcribed and phonetically tagged corpus of approximately 600 utterances (2643 word tokens) of conversational speech from 28 Brisbane high school adolescents, from grades 8-10, balanced for sex and school socioeconomic background (Ingram, 1989). 5.1. Methods and procedures Pre- and post-trauma utterances were digitized at 20kHz sampling rate and 8-bit quantization, using a speech signal processing program that facilitates phonetic observations and acoustic measurements. A phonemic transcription of each utterance was made, following conventions for Australian English used in the

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Macquarie Dictionary (Delbridge, 1985). The phonemic transcription, which may be thought of as a representation of the speaker's phonological target, was then annotated with phonetic process codes that were intended to capture significant phonetic transformations needed to map the phonemic transcription onto the equivalent of a relatively narrow phonetic transcription. See Appendix A for the transcribed and annotated pre- and post-trauma speech samples. The phonetic process annotations given in the appendix are numerically coded to reference the classification of phonetic processes shown in Table II. 5.2. Results The distribution of phonetic processes observed in the reference data set (speech samples from Brisbane adolescents) and the pre- and post-trauma speech samples is shown in Table II. The incidence of the processes in the reference corpus is presented as a normalised measure of rate of occurrence per 75 words. There were 77 and 79 words respectively in the pre- and post-trauma utterance sets. As expected, consonantal lenition processes and vowel reduction were the most common connected speech processes found in the reference data set. The pre-trauma utterance set had a profile of occurrence of phonetic processes which closely matched that of the reference data. The post-trauma utterance set also contained occurrences of common connected speech lenition processes (such as consonant cluster reduction, unreleased final stops, flapping of intervocalic alveolar stops). However, some vowel lenition processes (notably, vowel reduction and weak vowel deletion) occurred less frequently than might be expected from the reference data and the pre-trauma speech sample, and certain unusual or infrequent consonantal strengthening processes, which are described more fully below, appeared only in the FAS speech. The F AS speech conveyed an overall impression of unusual prosody: an overly regular rhythm, with a reduced range of stress, a tense, staccato delivery, and an unusual intonation contour. Some of these global suprasegmental features appeared to be attributable to the effects of phonetic processes, such as vowel shortening and glotallization annotated at the segmental level. In the subsequent discussion (Section 7) we address the question of causative mechanism, specifically we attempt to choose between the hypothesis of a disorder of timing and motor co-ordination and one of an abnormal articulatory setting. 5.2.1. Consonantallenitions These are processes that result in the attenuation of a constriction gesture or an assimilation to an accompanying vowel which tends to shift a consonant's manner of articulation to a higher level on the sonorance hierarchy. This category potentially included spirantization of stops, loss of frication turbulence on obstruents (gliding of fricatives, deaspiration of aspirated stops), flapping, vocalization (or vowelisation) of approximants, as well as voicing of phonemically voiceless consonants in environments of voicing assimilation. Examples of lenition processes that are common as connected speech processes in Australian English were found in both pre- and post-trauma speech samples (see Appendix A). In typical dysarthric speech, such as found in Parkinson's disease (Ingram, Murdoch & Chenery, 1988), lenition processes are exaggerated. Speech appears

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TABLE II . Phonetic processes in connected speech for F AS and Control speakers FAS speaker Pre-trauma* Post-trauma 1. Consonant lenition processes 1.1 Cluster reduction 1.2 Consonant deletion 1.3 Fricative weakening 1.4 Non-release of stops 1.5 Vocalization of /1/ 1.6 Flapping of It/

Reference data sett

Subtotal

6 2 1 3 1 1 14

4 4 1 2 2 _4 17

Subtotal

0 0 0 0 0

4 2 4 _3 13

0.6 0.0 0.2 __QJL 0.8

Subtotal

11 2 _6 19

2 3 _1 6

12.1 2.9 2.2 17.2

0 _ 0 0

3 _8 11

0.0 __QJL 0.0

0 _0 0

5 _2 7

0.7 __QJL 0.7

0 1 _0 1

3 1 _2 6

0.0 0.8 __QJL 0.8

1 _0 1 0

2 _1 3 14

0.0 __QJL 0.0 0.2

9. Final obstruent devoicing

0

14

1.5

10. Terminal contour change

0

4

0.0

2. Consonant strengthening processes 2.1 Stopping non-sibilant fricatives 2.2 Affrication of /s/ 2.3 Aspirated stop (non-initial) 2.4 Strengthening of sibilants 3. Vowel weakening processes 3.1 Vowel reduction 3.2 Vowel deletion 3.3 Monophthongization 4. Vowel quality change 4.1 Colouring of /'J/ 4.2 Full vowel quality change Subtotal 5. Quantity change (shortened/checked) 5.1 Vowel shortening 5.2 Consonant shortening Subtotal 6. Syllable structure changes 6.1 Vowel epenthesis 6.2 Weak syllable deletion 6.3 Resyllabification Subtotal 7. Assimilation processes 7.1 Place assimilation 7.2 Vowel devoicing Subtotal 8. Glottalization

7.2 1.3 1.7 5.1 0.9 ~

19.0

• Raw frequencies .

t Rate of occurrence /75 words.

"slurred". There is loss of segmental contrasts and intelligibility of individual sounds. Although there was some loss of consonantal contrasts in the post-trauma speech sample, the rate was no more than would normally be expected in connected speech and was perceptually overshadowed by some striking and unusual strengthening processes. For example, the initial /1/ in "she has let .. . " was deleted, but its syllable initial slot was occupied by a strongly fricated /s/ from the preceding · coda-processes of "fricative strengthening" and " resyllabification", yielding: [tf i?a

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set. .. ]. (Other consonantal fortitions illustrated in this example, shown in Fig. 2, are the affrication of the If I and the strengthening of the /h/ to a glottal attack.) A similar example of a potential consonantal lenition being masked by unusual strengthening may be seen in: "cookies from . . . "~ [khukhifom ... ] . Resyllabification here and elsewhere appeared to operate to simplify syllable structure in the direction of canonical CV forms. But basic consonantal constriction gestures were not weakened, as in other forms of dysarthria. 5.2.2. Consonantal strengthening In addition to the unusual affrication of voiceless sibilants Is/ and If I mentioned above, there was a tendency to aspirate voiceless stops in initial /s/ clusters ("stool"~ [sthul]) and to audibly release voiceless stops in word final position (e.g. , "washing up"~ [wofiiJ Aph]), including, phonologically voiced stops that had undergone final devoicing (e.g. "isn't married" [1znt mAridh]). Normally in Australian English, voiceless stops are unreleased and often glottalized in this position. The previous example also illustrates a clear change of vowel quality of phonemic magnitude (backing of /eel to a low central vowel, conventionally transcribed as IA/ (Bernard, 1970)) . The stopping of dental fricatives (e.g. "the"~ [
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"foreign accent". Eight instances of "full vowel quality change" were observed in the FAS sample. Three of these involved function words in environments where vowel reduction, though not likely, was possible. However, all changes involved low vowels (Ire/, /a/, /o/). There were four instances of /re/ "backing" to [a] or [A](/ A/ is the phonemically short counterpart of the low central long vowel /a/ in Australian English. Both have virtually identical vowel qualities.). There were four instances of the short low back rounded /o/ "fronting" to the central unrounded [A] or [a]. However, not all instances of /re/ and /o/ underwent perceptible shifts of vowel quality . Acoustic measurements of monophthongal vowel formant frequencies were undertaken on F AS speech samples. The pre-trauma recording was of too poor a quality to yield reliable formant measurements, so the subject was compared with three female control speakers, all Brisbane born, within 15 years of age of DS, and of similar physical stature and socioeconomic background. A reading passage, "The grandfather passage" was used to obtain the vowel formant measurements. F 1 and F2 measurements were made at estimated mid-points of primary stressed vowels. Average first and second formant measurements for all monophthongal full vowels are shown in Fig. 1. Varying numbers of tokens for different vowels are represented in the formant measurements. The measurements forDS are based on a total of 54 tokens and 162 tokens for the three controls . Some reduction in the overall acoustic vowel space, primarily due to a restricted F 1 range, is apparent from the formant chart. The "fronting" of [o], observed perceptually in the post-trauma utterance set is reflected in the formant measurements from the reading passage. The [re] did not appear to be significantly "retracted". However, acoustic contrasts among the low vowels appeared to be reduced, at least on the basis of F 1 and F2 measures.

1.1.-

Figure 1. First and second formant measurements for FAS speaker(.&-.&) and three controls (pooled) (e-- -e) , from readings of "The grandfather passage" .

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5.2.5. Quantity changes Shortening of vowels or consonants in connected speech usually accompanies phonetic reduction and would normally be regarded as a lenition process. However, several vowels and consonants in the post-trauma utterance set had a shortened or "checked" perceptual quality, which it did not seem appropriate to treat as lenitions because the segments in question retained perceptual prominence and acoustic strength. Four instances of shortening of phonemically long vowels or diphthongs were noted ("he", "boy", "falling", "twenty four"). Vowel shortening appeared to be related to glottalization. However, syllables that were perceived as "checked" because of a glottalized coda or following onset were not (doubly) tagged as "shortened" and "glottalized". Two instances of perceived consonant shortening were observed on sibilant fricatives in coda position. They appeared to be close relatives of the consonant strengthening process of "affrication" noted previously, in onset position. 5.2.6. Syllable structure changes In addition to syllable structure changes noted above, three unusual instances of vowel epenthesis were noted in the post-trauma utterance set (e.g.: "boy is on"~ [b:JI q:;::, An], "gets some"~ [ges;::~ tsAm]). Vowel epenthesis is not uncommon as a syllable structure simplification strategy, employed by second language learners, and may have contributed to the impression of "foreign accent".

5 .2. 7 Assimilation processes Only unusual assimilation processes, outside of the range of allophonic variation expected for connected speech in Australian English were tagged. No instances were encountered in the pre-trauma set. Two instances of unexpected place assimilation were observed in the post-trauma set: "two children"~ [tfu tf;::,ud3rm], "is thirty" [i~ §3ti]. There was also one case of vowel devoicing, in phrase final position before a voiceless obstruent. 5.2.8. Glottalization In Australian English, glottal constriction accompanies oral closure on voiceless alveolar stops before an alveolar nasal (e.g. "button" [bAt?n]), or occurs as a secondary articulation on unreleased voiceless stops in coda position, where it is often difficult to detect auditorally. However, in the post-trauma utterance set, glottalization occurred frequently (14 times) either as a fortis onset or coda, contributing to the impression of staccato delivery noted above. There were also two intrusions of creaky voice that were tagged as "glottalization" in the process analysis but which are distinguished in the narrow phonetic transcription in Appendix A. 5.2.9. Final obstruent devoicing This process is a phonetic tendency in Australian English, particularly in phrase final position. But it occurred more frequently and in a more prominent form in the FAS speech sample.

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5.2.10. Prosody and terminal contours DS's pre-trauma intonation contours, were unremarkable. There was little apparent pitch variation, possibly reflecting a certain lack of involvement in the interview. Her post-trauma intonation contours had a distinctly "non-native" quality. The F 0 traces of the post-trauma utterances tended to be quite flat overall, but with an exaggerated pitch change (usually a fall) on the last syllable of the phrase. This unusual terminal pitch contour, when perceptually prominent, provided a discrete prosodic feature that could be annotated, along with the other (basically segmental) features described above. Four instances of this feature were noted, an example of which is shown in Fig. 2. The waveform in Fig. 2 also illustrates the tendency of individual syllables to be temporally separated and of roughly equal amplitude, features which probably contributed to the perception of equal stress and syllable-timed rhythm. To provide acoustic confirmation of this unusual terminal feature, F 0 measurements were made at three equi-spaced points on the terminal contour and on the preceding, "pre-terminal" syllable. (See Appendix A for the loci of the terminal contours.) Of 17 terminal contours in the post-trauma set, 14 were classified as "falls", two as "low-rise", and one each of "rise-fall" and "high-rise". Only seven readily measurable terminal contours were found in the pre-trauma set, six "falls" and one "low-rise". A two-way ANOV A for unequal samples was conducted on the falling terminal F 0 contours. Main effects for group (pre- and post-trauma) and position were highly significant (F = 35.5, p < 0.0001; F = 13.9, p < 0.0004) and there was a significant interaction effect (F = 3.75, p < 0.015). The mean F 0 values are plotted in Fig. 3. The FSA terminal contours show a steeper fall from a higher pre-terminal level. This finding contrasts somewhat with Blumstein et al. 's case, in which exaggerated rising terminals predominated, although one example of an inappropriate high rise was found in: "I've two childrenrise a boy and girlfau".

li!_B

KH2

]

'

aoverfl

10-27-1991

21:36:36

Figure 2. Spectrogram, waveform and superimposed F0 contour for posttrauma utterance .

469

Foreign accent syndrome

200

180 N'

f,,,

2:. u:'

160

',+----

l

140 Preterminal

2

3

Terminal

Figure 3. Fundamental frequency measurements for falling terminal contours for pre- (e-- e) and post-trauma (e--e) utterances. Bars indicate standard error of the mean.

6. Multiple regression analysis To determine which phonetic processes contributed most strongly to the perception of "foreign accent" in FAS speech, a stepwise multiple regression analysis 1 was undertaken, using as independent variables, the ten phonetic process types shown in Table II and Foreign Accent scores as the dependent variable. 2 The 31 utterances from the pre- and post-trauma utterance sets were pooled for this analysis. Each utterance had 10 independent variable scores from the phonetic process analysis and the mean Foreign Accent scores from the perceptual rating experiment constituted the dependent variable. Results of the stepwise regression for the prediction of the Foreign Accent scores are shown in Table III. Four variables were extracted: Terminal contour change, Final obstruent devoicing, Consonant strengthening and Vowel quality change. Two process variables having substantial (univariate) correlations with the dependent variable, but which were not included in the m'o del by the regression analysis were: Syllable structure change (r = 0.55) and Glottalization (r = 0.52). 1 Multiple regression (Nie et a/. , 1975) is a technique for finding an optimal linear prediction equation between a set of independent or predictor variables and a dependent variable. Stepwise multiple regression is an iterative method of entering variables into a regression equation that seeks to optimize the prediction with as few terms as required. On each step of the calculations, the variable from the pool of not-yet-included predictors which accounts for the greatest portion of the variance in the dependent variable is selected, having regard to variables already included in the equation at the previous step. 2 The presence of a high proportion of zero values in the cells of the data matrix for some predictor variables does not invalidate their inclusion in the regression analysis, but might be expected to limit their usefulness as predictors. Such variables may be expected to behave like categorical variables.

470

J. C. L. Ingram et al. TABLE III. Stepwise regression analysis Dependent variable: Foreign accent rating scores* Independent variables included in model

Beta coeff.

Std. error Beta coeff.

Tvalue

p

Consonant strengthening Vowel quality change Final obstruent devoicing Terminal contour change

30.56 22.69 44.78 99.17

13.73 11.45 14.94 28.02

2.23 1.98 3.00 3.25

O.D35 0.058 0.006 0.003

* R 2 unadjusted= 0.71; R 2 adjusted= 0.66.

7. Discussion

We now turn to the problem of identifying the underlying nature of the production disorder in FAS. We shall weigh the observational evidence from the present study in an attempt to choose between two competing hypotheses: (a) that FAS speech symptoms arise from an abnormally tense vocal tract postural setting (Graff-Radford et al., 1986) and (b) that FAS represents a disorder of prosody caused by difficulties of temporal co-ordination or timing (Blumstein et al., 1987). On balance, the evidence from the present case, favours an interpretation of the postural adjustment hypothesis, but the timing hypothesis cannot be entirely excluded. Following Laver (1981), we take a "vocal setting" to be a tendency of the vocal musculature to maintain a specific long-term adjustment which provides an "articulatory bias", affecting different segments in varying degrees and ways, depending upon the particular setting employed. A Tense articulatory setting may involve (a) a generally raised level of muscular tension in the tongue, the soft-tissue walls of the vocal tract and the laryngeal musculature, (b) greater than normal excursion of the tongue and other articulators from the neutral position in the attainment of speech targets, and/ or (c) a specific articulatory bias characteristic of a tense vocal tract setting. Features (a)-(c) do not necessarily co-vary, and they have distinct acoustic and perceptual consequences. A raised level of muscle tension might be expected to manifest itself in a perceptual impression of "tense voice" (Laver, 1981), and to be reflected acoustically in sharper oral resonances (narrower formant bandwidths) and less high frequency damping of the voice spectrum. However, the perceptual characterization of "tense voice" is not particularly well established and the relevant acoustic measures could not be made in the present case. Hence, no direct evidence for (a) an overall increase in muscle tone or tension can be adduced from the present analysis, save for an argument that may be made on the basis of the terminal contours noted in the post-trauma speech, given below. The presence of consonantal fortitions and the lower incidence of vowel weakening processes are compatible with (b) above, more vigorous articulatory gestures . However, the restricted F 1 range that was found for vowels, which Blumstein et al. also noted in their subject , suggests reduced jaw movement. Increased activity of the tongue is not incompatible with reduced movement of the jaw. But the pattern for our subject would appear not to be one of generalized hyper- or hypo- kinesia as is found in some forms of dysarthria. There is some evidence, in the vowel quality changes, of an articulatory bias that

Foreign accent syndrome

471

has been attributed to a tense vocal tract setting. Ladefoged (1971) identified a "tense" articulatory setting, now labelled more specifically as "advanced tongue root" (ATR) (Ladefoged, 1982), which would be expected to differentially impact upon low back vowels. Laver (1981) also associated a tense vocal tract setting with a more forward posture of the tongue root and (although in this respect differing from ATR) a raised larynx setting. Comparison of DS's post-trauma formant chart with that of the controls is consistent with a postural change that affects the targeting of /o/, the only low back monophthong in Australian English . The raised mean F0 that was observed in the post-trauma speech sample is also consistent with a raised-larynx posture, which may accompany a tense articulatory setting (Laver, 1981). It is possible that the exaggerated terminal fall noted on most of DS's tone groups represents a release from a tense, phonatory setting. The prominent glottalization contributed to the perception of staccato rhythm, which has, in turn, been linked with a "tense" speaking style (Crystal, 1969). However, glottalization could also be a natural consequence of breaking speech up into isolated syllables, a possible strategy adopted by the speaker in the face of production difficulties. The sporadic deletion of segments in consonant clusters, resyllabification, and occasional non-standard assimilations that were observed are suggestive of residual production difficulties . It might be inferred from the abnormal voice onset time (VOT) lags associated with aspiration of the alveolar stop in "stool" that there were difficulties involving the timing or phasing of independent articulatory gestures. However, VOTs for singleton syllable-initial stops in the post-trauma speech sample and from other material elicited from the FAS speaker fell within normal ranges (see Appendix B). But not all features of F AS speech may be satisfactorily accounted for by an altered (tense) vocal tract setting. It remains difficult to see how a static postural readjustment, could, on its own account, affect the dynamics of rhythm and stress , which was one of the perceptual attributes of the FAS speech, though not the most salient. Nor of course, is it possible to separate the effects of habitual speaking strategies, which may have been adopted by the FAS speaker following her stroke, from any primary effects caused by the speech motor disorder. Both segmental and suprasegmental features were found to contribute to the perception of foreign accent. The intrusion of consonantal strengthening processes, vowel quality changes, and final obstruent devoicing were the most prominent segmental changes. Glottalization, syllable structure changes, and a perceived shortening of some vowels and consonants were features annotated at the segmental level, which probably contributed to the perception of altered stress and rhythm. Exaggerated terminal voice pitch changes, possibly caused by release from a hypertense vocal setting, contributed to the perception of a non-native intonation contour. The suppression of low-level lenition processes in connected speech and the presence of unusual consonantal strengthening processes, which contributed to the perception of "foreign accent", also appear to be by-products of an altered postural setting and suggest that the symptoms of F AS speech bear no specific relationship to the phonological system of the speaker.

References Ardila, A. , Rosselli , M. & Ardila, 0. (1988) Foreign accent: an aphasic epiphenomenon? Aphasiology, 2(5), 493-99.

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Bernard, J . R. L. (1970) Towards the acoustic specification of Australian English, Zeitschrift fur Phonetik, 23, 113-128. Blumstein , S. E ., Alexander, M.P., Ryalls, J. H., Katz, W. & Dworetzky, B. (1987) On the nature of the foreign accent syQdrome: a case study, Brain and Language, 31, 215-244 . Crystal , D. (1969) Prosodic systems and intonation in English . Cambridge: Cambridge University Press. Delbridge, A. (ed . in chief) (1985) The Macquarie dictionary, revised edition. Sydney: Macquarie Library Pty. Ltd. Esling, J. H . (1987) Vowel shift and long term average spectra in the survey of Vancouver English. In : Proceedings of the eleventh international congress of phonetic sciences, Vol. 4, pp. 243-246. Tallin : Academy of Sciences of the Estonian S.S.R. Graff-Radford, N. R., Cooper, W. E., Colsher, P. L. & Damasio, A. R . (1986) An unlearned foreign 'accent" in a patient with aphasia, Brain and Language, 28, 86-94 . Gurd, J . M. , Bessell, N. J., Bladon, R. A . W. & Bamford J. M. (1988) A case of foreign accent syndrome, with follow-up clinical , neuropsychological and phonetic descriptions. Neuropsychologia, 26(2), 237-251. Guyton, A. C. (1981) Textbook of medical physiology. Philadelphia: W. B. Saunders. Ingram, J . C. L. (1989) Connected speech processes in Australian English, Australian Journal of Linguistics, 9, 21-49. Ingram, J. C. L., Murdoch, B. E. & Chenery, H. 1988. Prosody in hypokinetic and ataxic dysarthria. In: Proceedings of the second Australian international conference on speech science and technology, pp. 350-355. Canberra: Australian Speech Science and Technology Association. Jordan, B. V. (1988) Ultrasound: sound manipulation software for IBM PC compatibles. St Lucia: UniQuest Ltd., University of Queensland. Ladefoged, P. (1971) Preliminaries to linguistic phonetics. Chicago: University of Chicago Press. Ladefoged, P. (1982) A course in phonetics, 2nd edn. San Diego: Harcourt Bruce Jovanovich . Laver, J. (1980) The phonetic description of voice quality. Cambridge: Cambridge University Press. Miceli, G. & Caramazza, A. (1988) Dissociation of inflectional and derivational morphology, Brain and Language, 35, 24-65. Monrad-Krohn, G . H . (1947) Dysprosody or altered 'melody of language', Brain , 70, 405-415. Nearey, T. M. (1978) Phonetic feature systems for vowels. Bloomington: Indiana University Linguistics Club. Nolan, F. (1983) The phonetic bases of speaker recognition. Cambridge: Cambridge University Press. Pick, A. (1919) Uber Anderungen des Sprach-characters als Begleiterscheinung aphasischer Storungen, Zeitschrift fur die gesamte Neural. Psychologie, 54, 230-241. Ryalls, J. H. (1986) An acoustic study of vowel production in Aphasia , Brain and Language, 29, 48-67. Wells, J. C. (1982) Accents of English, Vols 1 and 2. Cambridge: Cambridge University Press. Whitaker, H. A. (1982) . Levels of impairment in disorders of speech. In Neuropsychology and Cognition (R.N. Malatesha & L. C. Hartlage, editors), Vol. 1, (Nato Advanced Study Institutes Series D, No. 9). The Hague: Nijhoff. pp. 168-207.

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Foreign accent syndrome

Appendix A. Annotated pre- and post-trauma utterance sets See Table II for phonetic process codes. #=word boundary. Underlining= locus of terminal contour. Pre-trauma

twenti f3st ov disemb;}

No one of each nou WAn ov itf

11#

#

#31

No I'm a Capricorn nou aim ;} krepnbn

nou wAn ;}V itf Its all money you know people just going for money Its :>I mAni ju nou pipl d3Ast goUIIJ b mAni

#

#

#31#33#

#11#33- 31#31#

Its :>1 mAni j;} nou pipl d31 s gou;}n f;} mAni Oh yeah I see ou je;} a1 si

#33# ou je;} ai si

~res

nou aim ;} krepr;}k:>n That'd be alright t'lret;}d bi :>lrait

62#

#3 1 - 16 - 14

t'lre bi :>ran'

Yes he was in the war jes hi woz m ('I;} w:>

#

#31#13#

jes hi W;}Z

In ('I;}

W:l

#31#

;}n d3;}lai

Oh he should but he wont ou hi fud bAt hi wount

33#

#33#

#

Thats in July t'lrets m d3ula1

71-11

#31- 1z#

tweni f3st ;} disemb;}

#

#17#12#14

Post-trauma The woman is washing !!J2 ('I;} WUm;}n IZ WOfiiJ Ap

ou hi fud bAr i woun

21 #32 - 8#9# #23 Q;} wumn? I~ wofiiJ Aph

Ah Capricorn a krepnbn

and she has let the water overflow rend fi hrez let ('I;} w:>t;} ouv;}flou

#31 a krepr;}bn No twenty three nou twenti Sri

#11# nou tweni Sri sometimes I used to do a lot SAmtaimz ai just tu du ;} lot

#

#

#31#

sAmtaimz ai just !;} du ;} lot Oh a couple of times not very often ou ;} kApl ov taimz not veri oft;}n

#32#

#clit#33#14#

ou kApl;} taimz V;}ri oft;}n Does he like that dAZ hi la!k i'lret

31# d;)z hi Ia Ik t'lret He wouldn't like travelling much hi wAdnt laik trrev;}hl) mAtf

#1 1 -1 5 #

#3 2#

hi wudn laik trrevhl) mAtf Hasn't come up yet hreznt kAm Ap jet 11# # #t- rei hrezn kh Am Ap jet Twenty first of December

8-42- 11#22#8- 42#12- 9- 63# 23#8- 62-10 ?an tfi ?a ~et' t'li'l w:>tA oufiou

#41-

the boy is on a stool b:>I IZ on ;} stul

('I;}

21#8#9- 61- 8#42# d;} b:>I? I~;)? An ;} sthul

#23

gets some cookies from a jar gets sAm kukiz from ;} d3a-

11- 61#22#9- 63#12#8#10 ges;} tsAm kuki

~om

il
the stool looks like it is falling over ('I;} stulluks laik It IZ f:>hl) OUV;}

8#23- 8#13#8- 61#8#17#9#51#41#

t'l;! Sthu(? luk' ;:)? ?(aik If I~ f:>hl) OUVA he's getting cookies for the girl hiz getiiJ kukiz b ('I;} ggl -

12 -5 1-9- 52#1 7#9- 52#

i~ genl) khukhi~ b ('I;} g3l

That's about all t'lrets ;}baut :>1-

42#32 -17# t'lrets baur :>1 I've got two children a1v got tu tfiidr;}n

8-33#42-14#71#31-16-41 -10 ?a1 gAt--, tfu tf;}Ud3f!n

474

f. C. L. Ingram et a!.

Appendix A. (continued) he isn't married hi Iznt mrerid

a boy and girl :J b:" :Jnd Q3r

32#

12#9- 14#42 - 9- 23

#4 1 -1 1#

b:" en g3l

i I~nt' mArie;!

the girl is thirty five (jg g3l Iz !bti faiv

h::~s:Jz

21#

#9-71-24#

9#

Q:l Q3l

I~

h:>s:J~

horses are his life a hiz laif

§3ti faiV

#9#72 a hi~ l11.1f

she has five children Ji hrez fa1v tf Ildr:Jn

what else wotds

51#9- 24#

42#24

Ji

hre~

#31 -16-8

WAt£1S

fa1v tfgud3r?.n

and the boy is twenty four rend (jg b:" IZ twcnti b

Col does most of it kol dAz moust ov It

11#21#518#9#17- 51#10

42#

ren Q:J b::H?

1~

#

#

23

khal dAz moust ov It

swcnri b

Appendix B. VOT measurements: post-trauma speech Voice Onset Time (VOT) measurements (ms) from the post-trauma utterance set, supplemented by items from a picture naming task (Edinburgh Articulation Test) and sentence imitations. All measurements made from initial CV syltables of stress bearing words

Mean SD

p

b

75 68 25 46 28 53 74 29

06 19 18 12 15

d

k

83 60 61 54

22 30 20 15

64

13

30 32 39 42 67 51 51 62 47

80 27 15 80 27 29 09 11

50 13 69 23 21 04 12 06

g

21 25 28 28 26 22 35 29 27 13 04