A longitudinal study of vowel production in partial glossectomy patients

Journal of Phonetics (1992) 20, 209-224

A longitudinal study of vowel production in partial glossectomy patients Sandra L. Hamlet and Robin L. Patterson Department of Otolaryngology, Wayne State University, Detroit, M/48201, U.S.A .

Susan M. Fleming Harper Hospital, Detroit, M/48201 , U.S.A . Received 5th June 1990, and in revised form 6th August 1991

A longitudinal study of vowel production in a group of five partial glossectomy patients was undertaken . Results based upon vowel formant data revealed that the glossectomy patients were able to compensate for the loss of a portion of the tongue. Over a period of approximately three months following surgery the acoustical vowel distinctions improved , matching those present pre-treatment. Physiological mechanisms for the improvement in vowel formants included a more protruded tongue carriage and greater jaw height , although the latter was not maintained in some subjects after the initial three months . Refinements in phonetic contextual formant patterns did not appear until six months following cancer treatment. In normal subjects , radiographic data showed a higher jaw and more fronted tongue position for vowels in a lingual consonant environment , compared to a labial consonant environment. In glossectomy patients this pattern for tongue fronting was preserved in the early post-surgery period , but was less pronounced. Data recorded six months following treatment showed some evidence suggesting a shift to differentially greater tongue height as a correlate to higher F2 in a lingual consonant environment.

1. Introduction

Glossectomy patients, who have had tongue surgery for cancer, are usually able to compensate remarkably well during speech. Even total glossectomees may achieve moderately good intelligibility through unusual labial, mandibular and pharyngeal speech compensations (Goldstein, 1940; Brodnitz, 1960; Dugay, 1964; Donaldson, Skelly & Paletta, 1968; LaRiviere, Seilo & Dimmick , 1968, 1975 ; Sawashima, 1968; Massengill, Maxwell & Pickrell, 1970; Skelly, 1973; Amerman & Laminack , 1974; Bradley, Hoowever & Stell , 1980; Effron, Johnson , Myers , Curtin , Beery & Sigler, 1981 ; Morrish , 1984, 1988) . Speech compensations of partial glossectomy patients have been described as modifications of normal articulatory patterns (Skelly , Spector, Donaldson , Paletta & Brodeur, 1971; Hamlet , Mathog, Patterson & Fleming, 1990). Many partial glossectomees are heared as normal speakers , or at 0095-4470/92/020209 + 16 $03 .00/0

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least as fairly intelligible if not entirely natural sounding (Rentschler & Mann, 1980; Dworkin , 1982; Georgian , Logemann & Fisher, 1982; Pruszewicz & KrukZagajewska, 1984; Kumakura , 1985; Barry & Timmermann, 1980; Allison, Rappaport , Salibian, McMicken , Shoup , Etchepare & Krugman , 1987; Urage, Igarashi , Sugi, Matsuya & Fukuda , 1987) . Speech compensations are possible because of relatively equivalent forms of production. It is useful to distinguish phonetic equivalence found in normal variability from that which must be learned following an unfamiliar alteration in the oral environment . Normal variability in speech stems from the flexibility of voluntary acts-they can be altered to generate suitable outcomes from a wide variety of initial starting conditions (Folkins, 1985). When the alterations required are already in a person's repertory of experience, they can be accomplished almost instantaneously . Examples of flexibility are adjustments made by the tongue to speak normally with an artificially fixed jaw position , or with unpredictable jaw perturbations. Such immediate adjustments do not seem to depend on use of auditory or oral sensory feedback (Kelso & Tuller, 1983; Abbs, Gracco & Cole , 1984; Kelso , Tuller, Vaitkiotis-Bateson & Fowler, 1984). Adaptations in response to an unfamiliar oral alteration, which must take place through learning, are examples of plasticity. An unfamiliar situation of this sort would be presented by the introduction of a new dental prosthesis (e .g. Hamlet & Stone, 1976; Hamlet, Cullison & Stone, 1979; Hamlet, 1984, 1988), or surgical alteration of the anatomy. Adapative learning is thought to be mediated by error information based on acquired internal relationships among intial starting condition , the sensory consequences of movement in a particular context, and the sensory information actually generated by movement (Schmidt, 1975; Broekhuijsen & van Willigen, 1983; van Willigen & Broekhuijsen, 1983). Reports on the speech characteristics of glossectomees, with few exceptions, have been based on data recorded at only one point in time-anywhere from two weeks to more than 10 years post-surgery. Fletcher (1988) reported sequential palatographic data for three partial glossectomy patients, although the time post-surgery and the sequence of testing were not the same for all subjects. One of these patients, who was tested at approximately monthly intervals starting one month after surgery, showed a change in place of articulation for consonants (more posterior contact) accompanied by a larger area of contact. Another patient in this study, who was tested one year post-surgery, did not demonstrate a change in articulatory pattern between data sets collected three weeks apart. Hamlet, Mathog , Patterson & Fleming (1990) studied a group of five partial glossectomees, and found less tongue mobility during speech post-surgery than seen after subsequent radiation therapy. Factors considered were differentiation of tongue contour for vowels and consonant-vowel transitions, both determined relative to the jaw. Recovery of tongue function for speech was able to proceed in spite of the effects of radiation therapy, which are usually considered detrimental to function. The present longitudinal study on a group of partial glossectomy patients was designed to collect data prior to cancer treatment, and following specified stages of treatment. The same subjects were studied as in an earlier analysis (Hamlet et al., 1990), although the emphasis there was on recovery of tongue mobility and the effect of medical treatment, and later follow-up recordings were not yet available. Of interest in the present analysis is the acoustic characteristics of vowels spoken by

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partial glossectomees , and the process of learning compensatory articulatory patterns. The speech of glossectomy patients can sound essentially normal and quite intelligible, but be distorted in subtle ways, or harder to understand under difficult listening conditions. In studying the outcome of cancer treatment and the speech rehabilitation of such patients, it is difficult to find measures of function sufficiently discriminating to reveal change or improvement. The re-establishment of natural acoustical coarticulatory patterns on vowels is one measure which may serve that need .

2. Methods A longitudinal acoustic and radiographic study was done on the speech of a relatively homogeneous group of partial glossectomy patients. The cancer treatment protocol was the same for all the patients: surgery followed by radiation therapy. Data collection took place shortly before surgery, two to seven weeks post -surgery, four to ten weeks post-radiation therapy, and during a follow-up recording six months post-treatment. Data were also collected on one occasion for matched normal controls. 2.1. Subjects

Two groups of subjects were studied, five male partial glossectomees (ages 40-63) and five male normal controls (ages 35-56). Two patients spoke American Black dialect exclusively, as did two of the controls. The others spoke a General American dialect characteristic of the upper Midwest region . Table I summarizes the cancer surgery. All of the patients had surgery involving the floor of the mouth, which would include removal of part of the genioglossus muscle . Four patients had removal of a portion of the anterior tongue (20-40% ). Three had part of the jaw removed. Two of the partial mandibulectomys involved unilateral removal of a portion of the horizontal ramus, and the third involved removal of the anterior mandible. The surgical closure and reconstruction varied across patients (Hamlet et al., 1990). Patient 1 had a primary closure with the tongue surgical wound closed on itself anteriorly, and the remainder of the tongue sutured to the mandibular alveolar periostium. He was thus unable to raise the remaining tongue tip independently. TABLE

I. Cancer surgery undergone by the glossectomy patients

Site of surgery Patient

1 2 3 4 5

Size of tumor (em)

Anterior tongue

Floor of mouth

Partial mandibulectomy

2X3 5x4 2.5 X 3 5X6 4X4

X

X X X X X

X X X

X X X

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Patients 3 and 5 had excision of one side of the tongue anterior to the circumvallate papillae. Reconstruction utilized a dermal graft, which covers the surgical defect but leaves the remaining structures relatively free to move . Patients 2 and 4 had the largest tumors , and the surgical defect necessitated reconstruction with muscular flaps from the trapezius or pectoralis major. These flaps provide some additional bulk to the remaining tongue , but the flap portion itself remains adynamic. Patient 2 was left with most of his tongue surface, but the underlying anterior musculature and anterior portion of the mandible were removed . Patient 4 had a large portion of the tongue anterior to the circumvallate papillae removed, as well as a hemimandibulectomy. The cancer patients did not receive speech therapy during the period of study. Speech therapy was available to them, and was not withheld for research purposes. These patients expressed a preference not to participate in speech therapy, or felt that their speech was adequately intelligible. 2.2. Speech sample The speech sample analyzed consisted of nonsense words of the form "h::>CVC", spoken in response to precisely articulated live-voice models provided by a speaker of a General American dialect. The vowels were /i/, /ref, /u/ . Consonants (the same pre- and post-vocalic), were /p/, It/, /k/. Because of the need to limit radiation exposure there was only one repetition of each nonsense word, for a total of nine utterances per subject in each recording session.

2. 3. Videofluoroscopic data Radiographic data were of fluoroscopic images (lateral view) recorded on videotape at 30 frames/s . A digital timing signal from a videotimer (accurate to 0.01 s) appeared on the images. The subjects had completed a modified barium swallow test just prior to the speech recording, so that the tongue was coated with contrast material for better visualization . The head was not restrained. Spatial calibration was determined from a coin taped to the chin or a small accelerometer taped to the subject's throat, which appeared in the x-ray image. Acoustical recordings were made simultaneously on an audio channel of the videorecorder. The microphone was held by the subject about 6 em in front of the lips. Synchronization of the audio and video channels was accomplished by means of a button-triggered tone burst superimposed on the audio channel before each word , at the same time that the video timer was halted for three consecutive frames (Hamlet & Miorano, 1988). In later analysis this permitted the exact location of each video frame to be determined in relation to the speech audio signal. Frame-by-frame analysis of the radiographic data was done. The video frame corresponding to the midpoint of the vowel was identified and frozen by the videoplayer. A digitized version of this frame was captured for strorage in a computer. The digitized image was re-displayed on the monitor and digital tracings (Image Measure software) were done of the outline of the profile of the tongue, the inferior border of the mandible, and the horizontal plane of the bony hard palate posterior to the alveolar ridge. The traced image was then printed out using a video printer.

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J

Figure 1. Measurement strategy for lateral-view radiographic data . Jaw height (J) and tongue height (H) were determined relative to the plane of the hard palate . Tongue fronting (F) was the distance from the palata-a lveolar junction to the point of maximum tongue height.

Three measurements were made on the video prints using the plane of the hard palate as a reference (Fig. 1) : (1) Jaw height (J) was measured perpendicular to the plane of the hard palate . The inferior edge of the mental protuberance of the mandible was used as the measurement point, except in patients who had this portion of the jaw removed. In those cases a consistent point on the most anterior edge of the mandibular remnant was utilized . (2) Tongue height (H) was determined by the distance from the highest point on the profile of the tongue to the plane of the hard palate. (3) Tongue fronting (F) was then the distance from this highest point to the vertical plane intersecting the hard palate at the palato-alveolar junction. These measures of tongue height and fronting were chosen because they could be done on radiological data from all subjects, even those with substantial portions of the tongue missing . It cannot be assumed that these measures represent greatest vocal tract area constriction and greatest point of constriction in the sagittal plane. Comparisons of tongue contour relative to the jaw were also made . This was done by superimposing tracings of the tongue in different tokens, with the outline of the jaw as a reference. 2.4. Acoustic data Formant frequencies for the vowels /i/, Ire/ , /u/ were determined at the temporal midpoint of the vocalic portion of the speech signal. Microcomputer based speech signal analysis software was used (Micro Speech Lab) . The signal was low pass filtered at 4000Hz and digitized at 10 000 Hz. A 512 sample point time window was located at midvowel, and an FFf analysis run with "medium" smoothing (moving average of six points) to reduce the influence of individual harmonics. Formant frequency values were determined by cursor location at the center of the formant.

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Statistical analyses were done on group data. Because of the limited number of utterances available from each subject, the effect of each separate phonetic context could not be examined separately. Statistical significance was tested using nonparametric tests: the Mann-Whitney U-Test, and the Wilcoxon Sign Test for related measures, as appropriate. When individual subject patterns differed in some respect from the group pattern, this is mentioned in the text.

3. Results 3.1. General observations All glossectomy patients were able to utter understandable vowels, although as will be shown below, their formant values post-surgery were not necessarily in the normal range. With one exception, the patients were able to produce plosive closure and did so at the expected places of articulation for all consonant contexts although not necessarily using the normal point on the tongue surface to make the plosive contact, especially for It/. Even patient 1, who had the anterior tongue sutured down, could still make some kind of linguo-alveolar contact for It/. The one exception was patient 4 who was unable to achieve tongue contact for /t/ and /k/ post-surgery, but was able to do so in the post-radiation therapy data. Speakers of Black dialect glottalized the final unreleased lingual plosives (Michou, Hamlet & Jones, 1991); however, this study concerned vowel production and no differences in results were found for the Black dialect speakers. 3.2. Acoustic changes for vowels An acoustic vowel diagram plot of average formant data is shown in Fig. 2 for the glossectomees and normal speakers. Values for all plosive contexts are combined for each vowel. The top portion of Fig. 2 compares normal controls and patients pre-treatment. No statistically significant differences were found for comparisons between these two groups. The lower portion of Fig. 2 compares vowel formants at different stages of cancer treatment. Post-surgery there were major changes in vowel resonance, with the main effect being a lowering of F 2 for front vowels (p < 0. 05). This could be anticipated since the surgery removed considerable tissue from the anterior tongue and floor of the mouth. After radiation therapy, several weeks later, the F 2 values for /i/ and /re/ had increased (p < 0.01) and were not significantly different from those recorded pre-treatment. Two of the patients (patients 3 and 4) died from cancer recurrence before a six-month follow-up recording could be made. There was no evidence of recurrence at the time of post-radiation therapy testing. In the six-month follow-up data for the vowel /re/ (Fig. 2) the second formant decreased (p < 0.05) and there was a non-significant trend for F 1 to be higher in comparison to the post-radiation therapy data. These statistical comparisons were based only on data for the three surviving patients. This did not bias the results, because mean F 1 and F 2 values for /re/ for

Glossectomy vowels 200

Iii

215 I uI

300

F1 (Hz)

400

500 -

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600 700

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I CB I

200

Iii 300

F (Hz) 1

X

400

500 D--mon=3

600 700

2200

2000

1800

1600

1400

1200

1000

800

Figure 2. Acoustic vowel diagrams for vowels spoken by normals and five partial glossectomy patients.

these three speakers post-radiation therapy were 697 and 1621; very similar to the mean for the total group of five patients post-radiation therapy. 3.3. Acoustic phonetic contextual effects Thus far we have plotted average values for three different plosive contexts combined. In normal English speech there is " lawful variability" in formant values, resulting from the effects of coarticulation in different phonetic contexts (Stevens & House, 1963; Elman & McClelland, 1986). These effects are most pronounced for Fz. Table II summarizes coarticulatory influences on mean F 2 for the three plosive contexts studied here. Ranges of values were large especially for the cancer patient data. Statistical analyses were performed with all vowels combined, using withinsubject difference scores. For normals F2 was higher in both the /t-t/ and /k-k/ contexts compared to the /p-p/ context (p < 0.01). In addition, F 2 was higher in the /t-tl context than in the /k-k/ context in normals (p < 0.05). In the six-month follow-up data for cancer patients, F 2 was higher in both the /t-t/ and /k-k/ contexts compared to the /p-p/ context (p < 0.05), but there was no statistically significant difference in values between the /t-t/ and /k-k/ contexts. None of the other comparisons revealed statistically significant differences. The contextual effects on F2 did not appear to be influenced by ability to produce plosive contact. Patient 4, the only one unable to produce plosive contact

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216 TABLE

II. Average F2 (Hz) and ranges (Hz) in parentheses, according to phonetic context

Subjects Controls Patients Pre-surgery Post-surgery Post-radiation therapy Six-month follow-up

Vowel

/p-p/

/t-t/

/k-k/

/i/ /re/ /u/

2023 (450) 1508 (586) 1004 (508)

2129 (352) 1602 (274) 1363 (313)

2086 (332) 1609 (352) 1153 (352)

/i/ /re/ /u/ /i/ /re/ /u/ /i/ /re/ / u/ /i/ /re/ /u/

2020 (976) 1547 (352) 1082 (411) 1582 (1231) 1463 (313) 1164 (508) 1972 (684) 1629 (352) 1027 (274) 1933 (488) 1478 (157) 1022 (136)

1840 (898) 1613 (547) 1285 (254) 1641 (899) 1523 (273) 1176 (586) 2039 (1113) 1637 (371) 1223 (488) 2174 (410) 1465 (78) 1429 (400)

2051 (273) 1606 (468) 1101 (352) 1672 (1231) 1500 (527) 1062 (430) 2023 (684) 1691 (312) 1074 (195) 2135 (312) 1510 (19) 1094 (234)

post-surgery, showed the most nearly normal contextual relationships for F 2 among the patients post-surgery . The absolute values of his formants were abnormal, but his F2 in /pip/ was 332Hz lower than in /tit/, F 2 in /prep/ was 98Hz lower than in /tret/, but F2 in /pup/ was 29Hz higher than in /tut/. After radiation therapy when this patient had regained the ability to articulate /t/ and /k/ the contextual pattern for F 2 disintegrated.

3.4. Radiographic data Videoftuoroscopic data were consulted for insights into the physiological mechanisms responsible for the changes in vowel formants. Table III summarizes measurements of jaw height, tongue height and tongue fronting. In this table all consonant contexts are combined, which results in very wide ranges of values for each measure . However, statistical comparisons were done using within-subject difference scores which paired values in the same phonetic context. A significantly higher jaw position was found for the vowel /u/ post-radiation therapy compared to post-surgery (p < 0.05). Likewise a significant difference in jaw height for /u/ was found between the post-radiation therapy and six-month follow-up conditions, when comparing data for the three surviving subjects (p < 0.05). The jaw was lower in the six-month follow-up data. In spite of this , vowel formant data for the vowel /u/ were essentially unchanged . Similar, but non-significant , trends in jaw position across conditions were found for the other two vowels-a tendency for jaw position to be higher post-radiation therapy. However, large individual differences in direction of jaw adjustments were seen; patient 1 whose tongue tip was tethered , had the same or a raised jaw position in the six-month follow-up condition, whereas the other two patients had considerably lower jaw positions, which lowered the mean relative to that found post-radiation therapy.

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TABLE III . Average jaw height (mm), tongue height (mm) and tongue fronting (mm) for vowels as spoken by cancer patients. Ranges are in parentheses. Larger values of jaw and tongue height mean a lower position, since the measure was taken from the plane of the hard palate. Larger values for tongue fronting mean a more posterior position /i/

/~/

/u/

Jaw height Post-surgery Post-radiation therapy Six-month follow-up

68 (21) 65 (16) 67 (13)

72 (20) 69 (13) 72 (18)

68 (21)* 64 (13)* 70 (15)

Tongue height Post-surgery Post-radiation therapy Six-month follow-up

7 (6) 7 (10) 7 (5)

12 (8) 12 (14) 15 (5)

9 (9) 9 (11) 10 (7)

Tongue fronting Post-surgery Post-radiation therapy Six-month follow up

14 (13) 14 (23) 18 (20)

19 (26) 21 (30)* 33 (30)

27 (20) 26 (29) 29 (29)

*Difference statistically significant, p > 0.05.

There were no statistically significant differences in tongue height across conditions , although there was a non-significant trend for the tongue to be lower for /re/ in the six-month follow-up data, which would be consistent with the higher F 1 on /re/ at that time. There were no significant differences in tongue fronting between the post-surgery and post-radiation therapy conditions. A significantly more posterior tongue position was found in the six-month follow-up data for the vowel /re/ compared to post-radiation therapy (p < 0.05), and a non-significant trend for the point of maximum tongue height to be more posterior in the other vowels also. The vowel /re/ was the only one showing formant changes between the post-radiation therapy and six-month follow-up conditions. The more posterior tongue position, coupled with a secondary influence of greater jaw openness and lower tongue height in some subjects would be consistent with the formant changes seen. Not explained on the basis of these measures is the large increase in F2 for the vowel /i/ in the post-radiation therapy data. These particular measures evidently did not capture the salient physiological adj ustments responsible for vocal tract area modifications. Further information on tongue positional changes was sought by comparisons of tongue profile relative to the jaw. Representative tokens are shown in Fig. 3. Four of the patients showed evidence, consistent across phonetic contexts, of greater tongue base advancement for the vowel /i/ post-radiation therapy, with associated greater tongue height or protrusion. 3.5. Radiographic phonetic contextual effects

Relative to the issue of consonant contextual variation in F2 , the radiographic data were compared for the /p-p/ and /t-t/ contexts, which showed the greatest acoustical coarticulatory distinctions for F 2 in normal speakers. Statistical comparisons required grouping all vowels for adequate sample size, and the significant

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S. L. Hamlet et al. Post-sur~ery

Post-radiation therapy

1 ,

....

4

TONGUE',,

'\ \

I

I

~: 2

I

5

I

3

''

'

\

I

1

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Figure 3. Profile of the tongue relative to the jaw for the vowel / i/ in /tit/.

effects noted below only pertain to such group data. Figure 4 shows data for tongue height and fronting for the vowels separately, but limited conclusions can be drawn about contextual effects for the separate vowels owing to small sample size. In normal subjects higher F2 in the It-t/ context was associated with greater tongue fronting (p < 0.01), but no difference in tongue height. In patient data post-surgery as well tongue fronting was greater in the /t-tl context (p < 0.05), but tongue height was not significantly different. There were no significant differences between consonants in tongue fronting or height post-radiation therapy. In the six-month follow-up data tongue height was significantly greater in the /t-tl context (p < 0.05) , but not tongue fronting. Based on this type of patient data , with vowels grouped , there is some minor evidence for a change in articulatory emphasis toward greater association of tongue height differences with contextual F2 distinctions , rather than tongue fronting differences. Figure 5 shows the difference in jaw height for vowels comparing the /t-tl vs. the /p-p/ context. For normal subjects , with the vowel contexts combined, jaw height was greater in the /t-tl context (p < 0. 05). There was a non-significant trend for jaw position to be higher in the /t-tl context for six-month follow-up data also. 4. Discussion This study of spontaneous speech compensations was based only on a relatively small number of subjects, and data representing only one repetition of each

219

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Figure 4. Plots of average tongue height (H) relative to the plane of the hard palate, vs. average tongue fronting (F) relative to the palato-alveolar junction. Comparisons are made between vowels in the /p-p/ context (dots) and in the /t-t/ context (circles).

phonetic context per subject. The results must be interpreted as tentative, for that reason. The acoustic data revealed that the formant structure of vowels spoken by glossectomy patients did not remain stable in the first year following surgery. Over a period of months following surgery compensatory speech patterns were being learned, and the acoustic vowel distinctions improved. If no physiological compensations were employed, the nature of the surgery would have markedly increased cross-sectional areas in the anterior vocal tract, resulting in a lowering of F2 for front vowels. This was in fact found post-surgery. The mechanisms responsible for a later increase in F2 for front vowels, bringing them into the normal range post-radiation therapy, included fronting of the base of the tongue as part of a more protruded tongue posture, and some evidence for a slightly higher jaw position. This greater tongue protrusion was evident in comparisons of the tongue profile relative to the jaw, but was not reflected in our

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S. L. Hamlet et al. 5 4

td (mm)

3 2

I iI

5 4

dj 3 (mm) 2

I

IE

I

dj (mm)

I uI

6mo lt-tl vs. lp-pl contexts . Positive numbers mean jaw position was higher in the lt-tl context. N

P-s

P-rt

Figure 5. Mean difference in jaw height in the

measures of tongue height and fronting of the upper tongue surface relative to the plane of the hard palate. The measures of tongue height and fronting we employed were based on the profile of the tongue, and did not track a particular point on the tongue. Fleshpoint tracking would provide a comparison more amenable to anatomical interpretation. The lateral view profile of the tongue also does not provide information about the influence on vocal tract area contributed by left-right articulatory asymmetries (Hamlet, Bunnell & Struntz, 1986), which should have been considerable in this patient population owing to the nature of the surgery. Recall that patients 3 and 5, in particular, had only one side of the anterior tongue removed. It is important to appreciate that the tongue anatomy for these glossectomy patients was grossly abnormal. Measures of lateral view tongue profile changes, which have been correlated with formant changes in normals, may be less predictive for such patients. That is, protrusion of the tongue remnant which could materially alter the anterior vocal tract area, is not necessarily reflected in these particular measures.

Glossectomy vowels

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From a previous study using these same partial glossectomy patients (Hamlet et al., 1990), we know that recovery of tongue mobility was an important factor in speech improvement seen between the post-surgery and post-radiation recordings. In order to match vowel formants of pre-treatment vowels , something beyond mere recovery of previous tongue function is required. Different usage of the remaining tongue mass would have to be employed. A normal speaker does not utilize the full range of potential tongue extension for vowels , since tongue protrusion even beyond the lips and palatal contact for consonants can be performed , which require more extreme postures than for vowels . We surmise that the partial glossectomees in this study made use of this physiological reserve to adopt a more protruded tongue carriage for articulation of vowels as well . The contribution of the jaw to recovery of normal vowel formants was relatively minor and secondary. There was a trend for the jaw position to be slightly higher for all vowels in the post-radiation therapy data , which would have aided in achieving greater anterior vocal tract constrictions . However , the vowels showing greatest F2 changes in post-radiation therapy data (/i/ and / re/) and in six-month follow-up data (Ire/), were not accompanied by statistically significant jaw adjustments when data for all subjects were combined. It is interesting to note in the six-month follow-up data for patient 1, who had least anterior tongue mobility due to the suture , that he retained the raised jaw position . Lindau & Ladefoged (1989) have observed that speakers of English may show a degree of consistency in favoring certain trading relationships among the lips , mandible and tongue in achieving vowel distinctions. Generalized alteration in usage of articulatory structures (e.g. more protruded tongue carriage or generally greater jaw height) reveals functional changes related to plasticity. Gradual changes in range of jaw positions during speech after introduction of an experimental dental prosthesis would be an example of such plasticity also (Hamlet & Stone , 1976, 1978). The glossectomy patients studied here revealed a large degree of articulatory plasticity related to tongue carriage. The adjustments made were extensions of normal activity, which is implicit in the concept of plasticity . Coarticulatory patterns in second formant frequency as a function of consonant context were found for normal subjects. The radiographic data for normal speakers revealed that greater tongue fronting and a higher jaw position were associated with the /t-t/ context compared to the /p-p/ context. Thus for these normal speakers the acoustical coarticulatory effect of lower F2 in a labial plosive environment did not just result from greater lip protrusion or less lip opening on vowels in the /p-p/ context (as would be expected); rather, a multi-articulator contribution to the distinction was found . In acoustical data for patient groups, expected second formant coarticulatory patterns did not reappearuntil six months following treatment. Patients treated with surgery and radiotherapy for cancer of the tongue experience considerable alteration of oral anatomy and physiology . Surgical procedures change the anatomy, and depending on the type of reconstruction performed, may leave the patient with structures lacking in normal sensation and mobility, temporarily or permanently. During radiation therapy there is often local inflammation. The fibrotic effect of radiation therapy upon the local blood vessels, muscles, glands and nerves is well documented (Baker, 1982) . During healing from surgery and the process of radiation therapy, the patient is not in a stable physical condition. It is not

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particularly surprising that speech compensations during this period may be rather general and incomplete . Relative to coarticulatory effects , radiographic measures for patients post-surgery showed greater tongue fronting for vowels in the /t-tl context, as did normals, although normals showed it to a greater extent. The extent of differential tongue fronting found post-surgery , in the absence of differential jaw height, evidently provided insufficient acoustical consequences for measurable coarticulatory effects on F2 . Radiographic data post-radiation therapy did not show significant contextual variation for any measure . In the six-month follow-up data tongue height differences (and a trend for jaw height differences also) were associated with higher F 2 in the /t-tl context. It may be inferred from these limited data that there was a shift from tongue fronting to tongue height as an articulatory correlate of coarticulatory F 2 patterns. Such a shift could be considered an indirect consequence of compensatory articulatory adjustments . Coarticulatory differences in vowel articulation are thought to be related to the physical requirements of consonant production. Data from one patient unable to produce lingual plosive contact post-surgery appeared to contradict this assumption, although the results could be interpretated further. We speculate that when this patient lacked lingual plosive contact post-surgery, he was not attempting compensatory maneuvers to achieve that goal. Instead he may have relied on his accustomed neuromuscular patterns to drive an inadequate peripheral mechanism , thus forming quasi-normal coarticulatory configurations. Once he did compensate to achieve plosive contact , however , other articulatory influences emerged in the vowels. Coarticulatory differences in vowel articulation are assumed to represent "economy" of physical activity conditioned by consonant articulatory requirements (e.g. Lindblom , 1963; although see Liberman , Cooper, Shankweiler & StuddertKennedy, 1967). Articulatory economy does not imply strict governance by physiological limitations. That is , it may be physically possible to have less coarticulatory accommodation than actually seen. This viewpoint is well accepted with respect to mechanisms underlying vowel reduction in English (see, for example, Harris's 1978 discussion of the role of articulatory undershoot vs. purposeful articulation of reduced vowels). The fact that glossectomy patients with poorer physical capabilities showed fewer normal coarticulatory effects when they were achieving consonant closure in the early stages of compensation, suggests to us that physical limitations are not the ultimate explanation for the acoustical effects of coarticulation on vowels that we examined. In fact , certain coarticulatory phenomena might rather be evidence for some physiological "slack" in a system that is achieving its mechanical goals easily . This may contribute to what is perceived as naturalness in speech. Supported by Grant No . CA 43838 from the National Cancer Institute. Assistance m obtaining the x-ray data was provided by Lewis Jones , MD.

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