Speech task effects on acoustic and aerodynamic measures of women with vocal nodules

Journal of Voice Vol. 9, No. 4, pp. 413-418 ,~) 1995Lippincott-RavenPublishers. Philadelphia

Speech Task Effects on Acoustic and Aerodynamic Measures of Women with Vocal Nodules Christine M. Sapienza and *Elaine T. Stathopoulos University of Florida, Gahlesville, Florida. and *State UniversiO, of New York at Buffalo, Buffalo, New York, U.S.A.

Summary: Vowel prolongation is often used to evaluate disordered voice production. In light of previous findings showing that co-articulation has significant influence on laryngeal function measures, the practice of using prolonged vowels to represent a speech sample is questioned. To test whether disordered and normal voice during vowel production is generalizable to connected speech, three speaking tasks were investigated: sustained vowel prolongation, syllable repetition and reading. Statistical differences were found between these tasks for certain amplitude and time based laryngeal function measures for adult women with disordered and normal voice. However, for the specific measures which were statistically different, the actual numerical and perceptual differences may be quite small. From a clinical assessment standpoint, the choice of the speech task may not make an apparent difference in the objective evaluation of disordered voice. Key Words: Women--Vocal nodules-Task--Laryngeal.

laryngeal measures from glottal airflow and electroglottographic waveforms across the vowel prolongation [ae] and syllable repetition [baep] for young and elderly speakers with normal voice. Their findings showed that even though no differences in time-based measures of open quotient and fundamental frequency occurred as a function of speech task, both subject groups had larger glottal airflows during vowel prolongation. Hirano (4) considered that the speech context may have a significant influence on laryngeal function m e a s u r e s b e c a u s e o f c o - a r t i c u l a t o r y influences. It may be that a single section of a vowel segment is not representative of the vowel target in c o n n e c t e d speech because of articulatory undershoot (5,6). For normal voices, stop consonant influence on vowel segments has been demonstrated as an elevation of average airflow when in a conson a n t - v o w e l - c o n s o n a n t context (7,8). In addition to articulatory c o n t e x t u a l effects, word stress has been shown to effect laryngeal function measures (9,10). Specifically, Gobl (I0) found larger peak glottal airflow and maximum flow declination rate

In order to make judgements regarding the severity of impairment of disordered voice production, clinicians often ask patients to produce a sustained vowel. From that vocalization, the stability, endurance, and overall quality of the voice production are often rated (I). L a r y n g o s c o p i c assessment of disordered voice production is also typically based on the production of a vowel, commonly [i] (2). This task remains a key part of clinical protocols for voice evaluations because it is easily demonstrated by the clinician, easily produced by the patient, and thus is time efficient (3). But is the function of disordered and normal voice during vowel production generalizable to connected speech? Higgins and Saxman (3) compared

Accepted December 20, 1994. Address correspondence and reprint requests to Dr. C. M. Sapienza at Department of Communicative Processes and Disorders, 455 Dauer Hall, University of Florida, Gainesville, FL 3261 I, U.S.A. This work was presented at the Voice Foundation's 23rd Annual Symposium: Care of the Professional Voice, June 1994;Philadelphia, Pennsylvania, U.S.A. 413

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for vowels in a stressed context as compared to an unstressed context. The current study compares laryngeal aerodynamic and acoustic measures from women with normal voice and women with vocal nodules across three speaking tasks of vowel prolongation, syllable repetition, and reading. The specific predictions include (a) for both the normal voice group and the vocal nodule group, amplitude-based measures of sound pressure level, maximum flow declination rate, and alternating glottal airflow will be significantly higher for the vowel/a/within syllables and reading conditions than for the vowel prolongation; and (b) time-based measures of airflow open quotient and fundamental frequency will show no significant differences for both subject groups across tasks. METHODS Subjects The subjects for this study were 10 women (mean age = 24 years) with bilateral vocal fold nodules. Ten women with normal voice, matched for age, height, and weight (---5%), served as the control group. Criteria for subject selection included (a) normal articulation, resonance, and language ability as judged by a certified speech language pathologist, (b) passing a hearing screening at 20-dB Hearing Level for the frequencies of 0.5, 1.0, and 2.0 kHz; (c) freedom from symptoms of allergies or colds on the day of testing; and (d) no professional singing and/or voice training.

Rating of disordered voices Each subject's voice was rated from a digitized 200-rfi~ safiaple selected from the midpoint of a two second sustained vowel production/o/. The samples were adjusted for equal output with use of a programmable attenuator (Wavetek model 5PI27BB 12) and Quest Sound Level Meter (Model 155), and low-pass filtered at 4,200 Hz, (White Instruments, Model 4658) before being played to the raters' right ears at 74 dB (C) through SONY WMC6 headphones. The quality of the subject's voices with bilateral vocal fold nodules were judged to be mildly dysphonic by four certified and licensed speech pathologists. Speech sample Each subject produced three trials of the following: (a) maximum sustained vowel prolongation of Journal of Voice, Vol. 9, No. 4, 1995

[o]; (b) a syllable train of seven repetitions of [pa]; and (c) a reading passage developed to include a high representation of the vowel [a] in a CVCV context [papa] (see Appendix 1). For the reading task, only the stressed syllable of the word [papa] was included for analysis. The vowel prolongation task was alternated with the syllable repetition and reading conditions in order to avoid the effects of vocal fatigue on any one task. Each of the tasks was completed at a comfortable pitch and loudness level.

Equipment and procedures A circumferentially vented wire screen pneumotachograph mask, coupled to a pressure transducer (Glottal Enterprises model MS I00 A-2) was used to sense a wideband airflow signal. Digital inverse filtering was completed using CSpeech 4.0 to yield a glottal airflow waveform (11). The experimental literature suggests that aerodynamic parameters are useful in describing both normal (12,13) and disordered voice production (2,1416). A number of acoustic and aerodynamic measures were selected for investigation and are described in the following section. Amplitude-based measures Sound pressure level (SPL) The SPL of the task was obtained with use of the wide-band pressure transducer inside the pneumotachograph mask calibrated for a 15-cm mouth-tomicrophone distance (13,17). The wide-band pressure transducer's response extended from direct current to 4,000 Hz (fiat to 1,200 Hz), and therefore functioned as a microphone for the measurement of SPL. Maximum flow declination rate (MFDR) MFDR was obtained by differentiating the glottal airflow signal. It was defined as the largest negative peak of the differentiated airflow waveform (13). Alternating glottal airflow (AC flow) AC flow was defined as the amount of airflow from the maximum peak to the minimum valley of the glottal airflow waveform. It is the airflow that is modulated by the vocal folds during voicing (13). Time-based measures Fundamental fi'equency (F0) Fo was computed from the derived glottal airflow waveform.

SPEECH TASK EFFECTS ON WOMEN WITH VOCAL NODULES Airflow open quotient (0Q20%) OQ20% was defined as the time the glottis was open relative to the period of the cycle. Time points related to the instant of opening and closing were located on the airflow waveform at 20% of the maximum amplitude. The 20% level avoids baseline energy and at the same time includes a majority of the waveform amplitude (13). For the vowel prolongation, measures were made from a 200-ms window of the midportion of the sample. Four 100-ms windows extracted from the middle four vowel segments were measured from the syllable repetition. A 60-70-ms window of the midportion of the vowel [a] of the first stressed syllable of [papa] was measured for the reading task, which occurred 11 times throughout the reading. The window of analysis for the vowel in the reading passage was smaller (60-70 ms) as compared to the vowel prolongation and syllable conditions due to an increased rate of speech. All of the laryngeal measures were made using cursor-controlled computer algorithms specially written to function within the Cspeech software program. Statistical analysis Means and standard deviations of the three trials were computed for each of the subjects to yield trial means. The trial means were used to calculate group means and standard deviations. Remeasurement of - 1 0 % of the data for each dependent variable was also completed and Pearson r correlations were performed in order to establish reliability of measurement. All measures were found to be reliable upon remeasurement at p i> 0.01 (see Table I for the r values). To determine whether a univariate repeated measures analysis or multivariate repeated measures design should be used to test the within-subject contrasts of vowel versus syllable and vowel versus reading, a test of sphericity was completed (18). The test of sphericity examines whether the dependent variables have equal correlations between the T A B L E 1. Intrameasurer reliability for laryngeal

aerodynamic and acoustic measures Measure

r Value

S o u n d p r e s s u r e level M a x i m u m flow declination rate Alternating glottal airflow Fundamental frequency Airflow open quotient

0.963 0.961 0.978 0.998 0.952

All r values are significant at p <~ 0.01. n = 106, df = 104.

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T A B L E 2. Results of the test of sphericity of a set of

orthogonal components using a chi-square analysis, alpha level <~0.05 Measure

Chi-square

p Value

Sound pressure level M a x i m u m flow declination rate Alternating glottal airflow F u n d a m e n t a l frequency Airflow open quotient

11.687

0.001"

5.050

0.029"

4.689 4.049 14.020

0.041" 0.044 u 0.000"

" p ~< 0.05.

different repeated measures. If the results are significant beyond an alpha level of 0.05, then a multivariate design is called for. For all of the measures the results of.the sphericity test were significant, therefore a multivariate repeated measures setup was used rather than individual univariate analyses (19). The probability level was set at p ~< 0.05 for the multivariate testing. The between-subject factor was type of voice production (disordered vs. normal) and the within-subject repeated measurement factor was speech task (Table 2). RESULTS Acoustic and aerodynamic measures

Means and standard deviations for all measures for the disordered and normal voice groups' productions of the three speaking tasks can be found in Table 3. A summary of the statistical results for these measures can be found in Table 4. Means related to the main effects of voice type (disordered vs. normal) and task (vowel, syllable, reading) can be found in Table 5. Statistical main effect

Voice type AC flow was significantly higher for the disordered voice group than the normal voice group (see Tables 4 and 5). Task SPL and MFDR were significantly greater during the reading than during the vowel prolongation. F 0 was significantly lower for the syllable production than the vowel prolongation (see Tables 4 and 5). DISCUSSION Significant task effects were demonstrated for SPL, MFDR and F 0. Sound pressure level may Journal of Voice, Vol. 9, No. 4, 1995

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C. M. S A P I E N Z A A N D E. T. S T A T H O P O U L O S

TABLE 3. Task means and standard deviations o f the acoustic and aerodynanffc measures Jbr the disordered and

normal voice subject groltps

Disordered voice Vowel Mean SD Syllable Mean SD Reading Mean SD Normal voice Vowel Mean SD Syllable Mean SD Reading Mean SD

Sound pressure level (dB)

Maximum flow declination rate (L/s/s)

Alternating glottal airflow (L/s)

Fundamental frequency (Hz)

Airflow open quotient

79.05 6.19

297.53 213.55

0.245 0.202

207.24 36.45

0.663 0.103

79.12 3.65

273.29 106.65

0.245 0.127

200.63 25.40

0.655 0.046

81.53 2.83

353. I 1 184.61

0.215 0.113

195.02 14.37

0.628 0.074

75.72 5.77

224.79 45.50

0.142 0.030

220.53 22.94

0.657 0.077

75.55 5.70

192.59 49.74

0.147 0.034

201.65 21.86

0.621 0.062

77.81 6.18

296.94 58.30

0.167 0.029

21 1.46 19.58

0.626 0.124

have been higher for the reading task than for the vowel prolongation because of the co-articulatory influence of the high pressure characteristic of the [p] segment on the vowel. However, this effect was not seen for the syllable repetition. It may be that the slower rate of the syllable train production resulted in a lower subglottal air pressure of the preceding/p/segment (20), or the pressure of the vowel had adequate time to stabilize, thus demonstrating less assimilatory influence of the/p/segment. It is

also probable that all three tasks were not initiated at the same lung volume, which could influence the intensity of the productions. Finally, it is possible that the subjects simply spoke louder during the reading. All of the factors discussed previously could affect SPL during clinical evaluations. A closer examination of the SPL data shows a 2.5-dB difference between the vowel prolongation and reading passage. For practical purposes, this may not ap-

T A B L E 4. Restdts o f the multivariate analysis o f variance Jbr the acoustic and aerodynamic variables Variable

Sound pressure level

Maximum flow declination rate

Alternating glottal airflow

Fundamental frequency

Airflow open quotient

1.986 0.179

2.125 0.166

6.010 0.027"

1.089 0.313

0.130 0.724

8.922 0.003"

5.965 0.013"

0.142 0.869

3.826 0.047"

0.693 0.517

7.609 0.015"

4.856 0.044"

0.124 0.730

2.940 0.107

1.123 0.306

0.010 0.921

1.219 0.287

0.242 0.630

8.103 0.012"

1.464 0.245

1.215 0.326

0.098 0.908

0.028 0.972

0.834 0.455

0.505 0.614

Voice F p Task F p Contrasts Reading vs. vowel F p Syllable vs. vowel F p Voice x task F p

F, the F statistic for multivariate test of equality of mean vectors, d f = 1,15 for voice type and df = 2,14 for speech task and the interaction of voice type by speech task. " p <~ 0.05.

Journal of Voice, Vol. 9, No. 4, 1995

SP E E C H TASK EFFECTS ON W O M E N WITH VOCAL N O D U L E S T A B L E 5. M e a n s and standard deviations (SD) related to the statistical main effects o f task and voice type

TASK Sound pressure level (dB) Reading Vowel Maximum flow declination rate (L/s/s) Reading Vowel Fundamental frequency (Hz) Syllable Vowel VOICE TYPE Alternating glottal airflow (L/s) Nodule Normal

Mean

SD

79.345 77.094

5.293 5.995

320.07 254.71

254.74 140.10

201.23 215.06

22.60 26.98

0.235 0.152

0.145 0.032

pear to be a large decibel difference, since a justnoticeable difference in intensity for tones is - 0 . 5 - I dB (21). Although clinicians may not be able to detect the small SPL difference across complex speech tasks, SPL should still be considered an important variable to consider when objectively examining voice across speech tasks since SPL is correlated to other interrelated measures such as tracheal pressure, MFDR, and F 0 (12,22). The finding of greater MFDR for the reading condition is consistent with positive correlation results to SPL (12,23), thus supporting the relationship of these two variables. Higgins and Saxman (3) reported that elderly women produce a significantly higher Fo during vowel prolongation than during syllable production. They did not, however, find this effect for their young female subjects. In addition, they judged that during clinical evaluations of disordered voice a higher F0 is often produced during vowel prolongation than during the syllable production. The current study's measurement of Fo in women with vocal nodules support Higgins and Saxman's (3) clinical observations. Their explanations of why a higher F 0 occurs during vowel prolongations during disordered voice production included higher laryngeal height and increased vocal fold tension to maintain glottal closure in the presence of an impaired laryngeal mechanism. We agree with these hypotheses, but further postulate that the vowel prolongation task also represents a simpler motoric task that is not influenced by co-articulation of other sound segments. Honda (24) has suggested that differences in

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vowel F o can be related to the influence of tongue height on hyoid position. During vowel prolongation there is greater likelihood that an articulatory target can be met as compared to a vowel within the context of a complex speech production task (25). It is hypothesized that the laryngeal tension is elevated more during vowel prolongation than during syllable production because of articulatory factors, thus contributing to the finding of a higher Fo for both subject groups. The current findings lead to the conclusion that Fo is not the same during vowel prolongation as compared to contextual speech. Although the discrimination of frequency changes for tones is very acute (0.1-0.2%), it is likely that Fo differences across complex speech tasks would not be as perceptually salient to the clinician during the evaluation of voicel The trends of the mean data and the statistical results for OQ20% agree with Higgins and Saxman's (3) open quotient findings for young women with normal voice and extends to young women with vocal nodules. Open quotient is not statistically affected by the type of speech task. The finding of higher AC glottal airflows for the disordered voice group was discussed in a previous paper for this subject group by Sapienza and Stathopoulos (26). In general, Sapienza and Stathopoulos hypothesized that the higher AC glottal airflow for the disordered voice group could be related to their greater tracheal pressure during voice production and/or to a decreased stiffness in the vocal fold cover. Both increased tracheal pressure and decreased stiffness of the vocal fold cover can result in an increased amplitude of vibration (16,26). Because there was not a significant difference in SPLs between the two voice types, the hypothesis that higher AC glottal airflows for the disordered group may be related to a decrease in vocal fold stiffness may be the more likely-alternative in explaining the AC glottal airflow finding. In addition, in the current study, AC glottal airflow was not shown to be affected by the type of speech task. The lack of a task effect is contradictory to the findings of Higgins and Saxman. However, in their study an age-by-task effect characterized by a significantly greater flow amplitude for vowel prolongation and syllable repetition for elderly versus young men was reported. It may be that the inclusion of the elderly men in their study influenced the larger flow amplitude during the vowel prolongation. Journal of Voice, Vol. 9. No. 4, 1995

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C. M. SAPIENZA AND E. T. STATHOPOULOS

CONCLUSION Vocal function of disordered and normal voices was investigated across three speaking tasks. The results of this study generally agree with previous reports in the literature that have studied task effects on laryngeal measures from the normal voice and extends those to the disordered voice. Certain amplitude- and time-based measures are significantly different for vowel prolongation produced by speakers with disordered voices when compared to vowels within syllable and reading. From a statistical viewpoint, some of the measures showed distinctions between task type indicating that vowel prolongation may not be representative of more dynamic speaking tasks. On the other hand, for the specific measures that were statistically different across tasks, the actual numerical and perceptual differences may be quite small. From a clinical assessment standpoint, the choice of the speech task may not make an apparent difference in the objective evaluation of disordered voice. A c k n o w l e d g m e n t : T h i s r e s e a r c h was s u p p o r t e d b y a g r a n t from the N a t i o n a l I n s t i t u t e s o f H e a l t h / N I D C D : DC00516.

APPENDIX Reading Passage Papa was a great man. Working all his life as a carpenter, he built homes for other people. Papa was an excellent craftsman. Anyone who worked with Papa knew that he was an honest man. Papa gave himself to his work, toiling daily for small amounts of money. No one disliked Papa. In fact, neighbors used to bring Papa apples, pears and other fruits, especially around the holidays. I remember Papa for his kind ways. What I remember was the manner in which Papa dressed, the way he carried himself. Papa was such a strong man. Devoted to his family, especially his children, Papa worked night and day to provide for us. Although we never showed Papa our appreciation on a daily basis, I know that he felt our love, or so I hope. REFERENCES 1. Wilson DK. Voice problems in children. Baltimore: Williams & Wilkins, 1987. 2. Colton RH, Casper J. Understanding voice problems: physiological perspective f o r diagnosis and treatment. Baltimore: Williams & Wilkins, 1990.

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19. Finn J, Bock RD. Multivariance. Chicago: Scientific Software, 1988. 20. Netsell R, Lotz WK, DuChane AS, Barlow SM. Vocal tract aerodynamics during syllable productions: normative data and theoretical implications. J Voice 1988;5:1-9. 21. Durrant JD, Lovrinic JH. Bases o f hearing science. Baltimore: Williams & Wilkins, 1977. 22. Titze IR. Principles o f voice production. Englewood Cliffs, N J: Prentice Hall, 1994. 23. Stathopoulos ET, Sapienza CM. Respiratory and laryngeal measures of children during vocal intensity variation. J Acoust Soc Amer 1993;94:2531-43. 24. Honda K. Relationship between pitch control and vowel articulation. In: Bless DM, Abbs JH, eds. Vocal fold physiology: contemporary research attd clinical issues. San Diego: College-Hill Press, 1983;286-97. 25. Stevens K, House AS. An acoustical theory of vowel production and some of its implications. J Speech Heat" Res 1961 ;4:303-20. 26. Sapienza CM, Stathopoulos ET. Respiratory and laryngeal measures of children and women with bilateral vocal nodules. J Speech Heat" Res 37:1229-42.