Vocal indices of biological age

Journal of Voice

Vol. 1, No. l, pp. 31-37 © 1987 Raven Press, New York

Vocal Indices of Biological Age R o b e r t L . R i n g e l a n d * W o j t e k J. C h o d z k o - Z a j k o Department of Audiology and Speech Sciences, *Center for Research on Aging, Purdue University, West Lafayette, Indiana, U.S.A.

resonance are usual in old age and that they result from diminished strength and elasticity of the laryngeal musculature (11). Studies of voice perception suggest that untrained listeners can accurately make judgments about a speaker's age from voice cues. Ptacek et al. (8) found that sufficient information for very high accuracy age judgment was available even in isolated sustained vowels and that the listener's proficiency increased dramatically when connected discourse was the speech sample. Shipp and Hollien (12) demonstrated that inexperienced listeners can reliably categorize speakers into young or old groups and that judgment accuracy increases as a function of the advancing age of the speakers. In the Ptacek study, judges listed the features that they felt helped them in making age judgments as "phrasing, speed, hesitancy, voice breaks, and vitality." While such descriptive terms of vocal performance are interesting, it is not yet known specifically which acoustic properties of the vocal signal aid in making perceptual judgments of a speaker's age. Changes in the larynx and in phonation are, of course, only a small part of the changes that occur in total body anatomy, physiology, and function which come about in senescence. Although it appears that there is a general decline in overall motor and sensory performance as an inevitable consequence of old age, there are often considerable differences between subjects in the rate and extent of such decline (13). In fact, one of the most robust findings in aging research is the extreme individual variation with which motor performance decline occurs. Both intraindividual variability (individual inconsistency in performance) and interindividual variability (group heterogeneity) increase with age (14). There is also good reason to believe that the

There can be little doubt that there is a generally accepted stereotype of the aging voice. We find evidence to support such a view in the judgments we make daily about a speaker's age from telephone and radio voice cues and by watching stage performers use voice as a means of establishing a character's age in the minds (and ears) of an audience. The issue has even found reference in the writing of Shakespeare, who described the sixth age of man as being marked by his "big manly voice turning again toward childhood treble, pipes and whistles in his sound." Strong evidence that laryngeal structure and function deteriorates with advancing age has been often reported. Clinical and postmortem studies have shown that the cellular, structural, and neurological integrity of the laryngeal system is increasingly compromised as the individual approaches the final stages of life. Significant age-related degenerative changes include muscle atrophy (1), ligamental deterioration (2), and catilagenous calcification (3). In addition to neuronal atrophy (3), neurotransmitter deficiencies (4) and nerve conduction velocity decrements (5) have been observed, both peripherally at the neuromuscular junction and also in central nuclei critical to the control of the larynx. It has also been well documented that certain parameters of phonation are altered with advancing age (6). Older male speakers exhibit lower fundamental frequencies (7), are less able to sustain prolonged vowels (8), have reduced maximal vocal intensities (9), and generally show atypical patterns of voice fundamental frequency variability (10). Hodkinson reported that changes in voice pitch and Address correspondence and reprint requests to Dr. R. L. Ringel, Young Graduate H o u s e , Purdue University, W. Lafayette, IN 47907, U.S.A.

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pattern of age-related deterioration is sometimes susceptible to modification through the implementation of specific interventional strategies such as exercise, good nutrition, and healthful life styles (15). Spirduso (14) makes the point clear that muscle disuse generally parallels aging, and disuse causes a loss of fast twitch fibers that is very similar to the loss seen in aging. She goes on to cite literature which reports that daily endurance training prevented the attrition of both slow and fast twitch fibers, which suggests that individuals who establish a life style of daily exercise may more successfully maintain the capacity to recruit fast twitch fibers. Following the line of reason that suggests that life style may affect motor performance, Spirduso also reports literature which suggests that exercise may have other effects that are beneficial not only to muscle contractility but to other peripheral mechanisms such as spinal reflex loops. By stimulating blood flow, exercise may enhance contractility and permeability of blood vessels, thus preventing local ischemia. She concludes by stating that healthy circulation maintains temperature in the extremities, which may in turn enhance functions such as nerve conduction velocity. Finally, the individuality of aging is also reflected in anecdotal reports of senior persons who daily perform extraordinary physical feats that are the envy of persons many years their junior, and of professional performers who are able to maintain their singing and acting voices into their seventh and eighth decades. The awareness of the potential uniqueness of age-related changes within and between individuals of the same chronological age have led investigators to develop measures of biological age that attempt to take into account physiological factors as major features in the aging process (16-18). Ringel and his associates in discussing phonatory processes have suggested that chronological age alone, with no account taken of other factors that occur concurrent with the passage of time, is an inadequate metric for the evaluation of senescent changes in behavior. They have shown that individuals of identical chronological ages may exhibit markedly different levels of sensory, motor, and cognitive performance (19-21). To date, few studies have addressed the existence of possible relationships between biological factors and the rate and extent of age-related changes in laryngeal performance. There are, howJournal of Voice, Vol. 1, No. 1, 1987

ever, reasons to believe that an individual's overall physiological status may influence vocal performance. Laryngeal control is known to be dependent upon a delicate balance of pulmonary, laryngeal, resonator, and other articulatory elements, which in turn are dependent upon the structural and functional integrity of the neural, endocrine, skeletal, and muscular systems. Disruptions in the function of any of the above systems can potentially result in diminished vocal quality and have been reported in both aging and disease. Although it has yet to be established that healthy lifestyles can have a beneficial effect by slowing age-related changes in laryngeal performance, there are a relatively large number of studies that suggest that diseased patients with poor overall physiological health exhibit vocal characteristics reminiscent of considerably older individuals. Indeed the relationships between vocal performance and disease are sufficiently common that dysphonic changes are frequently of great assistance in the differential diagnosis of certain diseases (11,22,23). For example, pulmonary diseases frequently disrupt air flow in such a way as to reduce the intensity, fundamental frequency, and duration of phonatory output (24). Coronary artery disease has also been shown to be associated with characteristic voice irregularities, conceivably as a result of both general respiratory inadequacy and also impaired laryngeal and pulmonary blood supply (25). Consistent with this finding, it has been reported that changes in the quality of voice may be an important diagnostic sign in selected cases of hypertension (26). Diseases that weaken respiratory and laryngeal musculature, such as myasthenia gravis, amyotrophic lateral sclerosis, late Huntington's disease, muscular dystrophy, severe hypokalemia, and malnutrition, have also been shown to reduce an individual's respiratory resources for normal voice production. The acoustic consequences of these disturbances are frequently manifested in inappropriate fluctuations in vocal intensity and fundamental frequency, particularly toward the end of the respiratory cycle (27). Finally, diseases of the CNS frequently affect the central integration of laryngeal control. Strokes, degenerative diseases, cortical and cerebellar tumors, Freiderich's ataxia, and multiple sclerosis all have been shown to be associated with increased variability in phonatory output (22,23). We have seen thus far that individuals even of the same chronological age may vary in the way in which they age and that an individual's health may

VOCAL I N D I C E S OF B I O L O G I C A L A G E

well be reflected in his or her voice. Despite these observations, in the past, most studies of aging and the voice have made virtually no attempts at acknowledging the potential of physiological differences between subjects as a source of experimental interest. However, in a current series of experiments, investigators from the Purdue University re:search group have attempted to determine the extent to which physiological health differences between subjects influence the degree of deterioration observed in the vocal performances of elderly subjects. In the first study, the relationships between laryngeal function and underlying body physiology were studied in a sample of 48 men representing three chronological age groupings (25-35, 45-55, 65-75 years) and evaluated by resting heart rate, systolic and diastolic blood pressures, percentage of body fat, and forced vital capacity. Voice samples were collected for all subjects during the performance of four phonatory tasks: extended vowel phonation, spontaneous speech, oral reading, and production of a maximal phonatory range for a vowel (19). A fundamental frequency analysis program was used to measure mean fundamental frequency (Fo), pitch perturbation (jitter), amplitude perturbation (shimmer), and phonation range from the acoustic samples. Maximum phonatory range and F 0 were included since these measures have frequently been adopted in previous studies for the assessment of age-related changes in acoustic performance. Jitter and shimmer were included since they have been shown to be particularly sensitive to minute temporal and mechanical irregularities in vocal fold vibration which are thought to be characteristic of the aging voice (6). Normative physiological data for subjects in the good and poor condition groups were obtained and are presented in Table 1. Since the groups were divided on the basis of fitnesS, as expected, there were considerable differences between the good and poor condition groups on all of the physiological variables. These data reinforce the notion that there are often considerable physiological differences between individuals of the same chronological age. Mean values and associated standard deviations of fundamental frequency, shimmer, jitter, and phonatory ranges for the extended vowel phonations were determined for these subjects and are presented in Table 2. A major finding of the study was that subjects in

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good physiological condition produced maximum duration phonation with significantly less jitter and shimmer and had larger phonatory ranges than did subjects of the same age who were in poorer physiological condition. The phonatory differences between groups were most apparent in the oldest subgroup studied. There were no differences between subjects with regard to mean fundamental frequency. These data support the notion that measures of pitch and amplitude perturbation are more sensitive to subtle differences in laryngeal performance than more traditional measures such as fundamental frequency. Furthermore, when the results of the study were analyzed only in terms of subjects' chronological ages, age-related changes in laryngeal function were quite limited. Shimmer was the only acoustic measure that varied significantly between young and elderly subjects. No significant age-related differences were observed for jitter, fundamental frequency, or phonatory ranges. Thus, if these findings alone had been reported, the relationship between physiological status and acoustic performance would have remained undetected. In a further analysis, vowel spectral noise levels ~vere examined in the same group of subjects (28). Vowel spectral noise levels were correlated to a greater degree with physiological condition than with chronological age. When spectral noise levels were studied in relation to speakers' chronological ages alone, noise levels and aging (defined chronologically) were not significantly related. However, when physiological factors were taken into consideration, the results indicated that vowel spectral noise was indeed related to an individual's progression in the physiological aging process. Data from both studies suggest that while chronological age is undoubtedly a major contributing factor to changes in the acoustic characteristics of voice, a speaker's overall physiological condition also plays a significant role in such change. Correcting for differences in physiological fitness between subjects was shown to result in a more appropriate grouping of subjects. This procedure had the effect of reducing intragroup variability and thus increased the ability to detect phonatory differences between subjects. A follow-up study was designed to examine these relationships in greater detail. Forty-nine male subjects of mean age 61 years were selected for the investigation. For the evaluations of physiological health, the pulmonary, hemodynamic, and anthropometric measures collected in the initial studies Journal o f Voice, Vol. 1, No. 1, 1987

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T A B L E 1. Mean values and associated ranges for the physiological measures

Age

Resting heart rate (bpm)

Systolic blood pressure (mmHg)

Diastolic blood pressure (mmHg)

Fat (%)

Forced vital capacity (L)

Mean Range Mean Range

29.5 26 - 35 32.3 25-38

55.9 44 - 64 85.5 68-110

124.8 115-140 154.6 136-170

76.3 70-80 98.0 88-100

16.1 14-20 30.5 25-34

5.16 4.52-6.47 5.04 3.77-6.25

Mean Range Mean Range

53.0 46-56 52.6 42-59

59.9 52-68 73.5 50-88

121.5 116-128 161.3 138-180

76.8 70-84 95.8 82-100

18.0 15-22 28.1 23 - 3 5

5.02 4.16-7.30 4.26 3.23 -6.00

Mean Range Mean Range

67.5 62-75 69.1 64-74

62.5 56-76 82.8 72-94

131.8 118-142 163.0 154-174

76.4 68-80 92.0 80-100

18.7 15-21 26.8 22-37

3.97 2.68-5.05 3.41 2.03-4.26

Groups Young age Good condition Poor condition Middle age Good condition Poor condition Old age Good condition Poor condition

were augmented by the addition of resting metabolic rate and blood lipid and cholesterol values. Subject scores on these variables were reduced to a single score indicative of overall physiological fitness (20). Subjects were also asked to perform a series of phonatory tasks including maximally prolonged vowels, connected discourse, and maximal phonatory range. Acoustic perturbation analyses were performed using a Glottal Imaging by Processing External Signals (GLIMPES) procedure for the extraction of glottal parameters from glottographic waveforms present in acoustic signals (28). This approach, which uses synthetic modeling strategies to optimize the extraction of vocal parameters, is particularly well suited for use in the detection of phonatory irregularities associated with impaired laryngeal function. Measures of fundamental frequency, maximum phonatory range, jitter, shimmer, and

spectral harmonics-to-noise ratios (H/N) were obtained for all subjects. The subjects were divided into two discrete good and poor condition groups. Subjects in the good condition group (N = 15) were selected because they scored at least one-half a standard deviation above the mean on the Index of Physiological Status, whereas the poor condition group (N = 15) scored at least one-half a standard deviation below the mean. The Index of Physiological Status has been described elsewhere (29). Table 3 summarizes the normative data for the physiological measures derived from the good and poor condition groups. As expected, grouping of subjects into good and poor condition groups resulted in significant physiological and biochemical differences between these groups. Table 4 presents means and standard deviations for phonatory measures collected during sustained

T A B L E 2. Means and standard deviations o f Fo, shimmer, and jitter for the extended v o w e l / a / F 0 (Hz) Group Young age Good condition Poor condition Middle age Good condition Poor condition Old age Good condition Poor condition

Shimmer (dB)

Phonatory range (Hz)

Jitter (%)

X

SD

X

SD

X

SD

X

SD

129.7 140.5

16.7 25.2

0.20 0.29

0.05 0.33

0.40 0.51

0.04 0.14

32.2 26.7

8.8 7.1

128.5 125.7

20.8 22.8

0.28 0.34

0.14 0.25

0.47 0.51

0.06 0.17

28.3 26.8

8.7 3.6

116.6 132.9

24.9 23.7

0.31 0.52

0.11 0.23

0.59 0.69

0.11 0.26

31.4 24.3

4.4 7.1

SD, standard deviation.

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T A B L E 3. Normative physiological data f o r subjects in good and poor condition Weight (kg)

Age SD

X

SD

X

57.1

14.8

81.1

9.4

128.2

67.5

7.4

83.8

11.5

143.6

Group Good condition Poor condition

SBP (mmHg)

DBP (mmHg)

SD

9.46 10.9

FVC (L)

FEV1 (L)

TRIG (mg/dl)

Cholesterol (mg/dl)

X

SD

X

SD

X

SD

X

SD

X

SD

76.9

8.5

4.6

0.52

3.8

0.40

87.0

23.0

195.4

40.5

82.4

4.9

3.2

0.72

2.4

0.53

151.4

72.4

222.5

29.2

SBP, systolic blood pressure; DBP, diastolic blood pressure; FVC, forced vital capacity; FEV1, forced expiratory volume (1 sec); TRIG, triglycerides.

vowel phonation. Physiologically healthy individuals exhibited less vocal jitter and shimmer and also had higher harmonics-to-noise ratios, suggesting that increased laryngeal control is associated with better physiological health. As with the previous studies, mean fundamental frequency was not found to be a sufficiently sensitive measure for the detection of differences between subjects of differing physiological conditions. Vocal insufficiencies were found to be most apparent in the analysis of prolonged vowels. In order to determine the influence of physiological factors on laryngeal performance independent of chronological age, a multiple discriminant function procedure was adopted to determine whether speech performance items could discriminate between two groups of high and low physical fitness that were matched for age (Table 5). Subjects in group 1 (n = 10, mean age 65.7 years) scored at least one-half a standard deviation above the mean on the Index of Physiological Status, whereas subjects in group 2 (n = 10, mean age 65.2 years) scored at least one-half a standard deviation below the mean. The discriminant function analyses revealed that the subjects in the better physiological health group had significantly greater phonatory control. Highly fit subjects exhibited less vocal jitter and had higher spectral harmonics-to-noise ratios. When the dis-

criminant canonical was applied for classification purposes, subjects could be classified into the appropriate health group with 75% classification accuracy. These data emphasize the importance of physiological health measures by focusing on speech performance differences b e t w e e n individuals with relatively extreme physiological profiles. The results support the findings of our previous studies in that subjects in good physiological condition perform vocal tasks in a manner quite different from those in poorer physiological health. In addition to establishing relationships between physiological variables and acoustic data, a further experiment was designed to determine whether these measurable differences in phonatory behavior observed between subjects were correlated with perceptually noticeable differences when presented to listeners. Allen (30,31) has shown that changes in laryngeal function can have significant impact on the perceptual characteristics of both the aging and diseased voice. In this preliminary study, 35 listeners of mean age 25 years were asked to estimate the ages of the subjects in the study after listening to them read a standard passage. In agreement with previous research (12), listeners' perceptions of age were found to be highly correlated with the subjects' chronological ages (r = 0.74, p < 0.001). Furthermore, subjects in good overall physiological condition were consistently judged to have

T A B L E 4. Means and standard deviations for extended vowel phonation Fundamental frequency (Hz)

Harmonics-tonoise ratio

Shimmer (dB)

Group

X

SD

X

SD

Good condition Poor condition

123.1

8.6

19.7

4.8

130.6

16.6

16,9

2.7

Jitter (%) SD

X

SD

2.9

1.3

2.34

1.77

4.3

2,2

3.12

1.67

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R. L. R I N G E L A N D W. J. C H O D Z K O - Z A J K O

T A B L E 5. Discriminant function analysis between high and low physiological status groups m a t c h e d for age Standardized canonical discriminant function coefficients

Variable Jitter (%) H/N

0.7424 0.9611

Chi-squared Canonical correlation Wilk's lambda Probability % correct classification

8.82 0.63 0.59 0.01 75%

younger-sounding voices (r = -0.36, p < 0.005). In addition, the associations between perceived age and physiological condition were once again found to be strongest for the oldest group of subjects (over 60 years, r = -0.32, p < 0.05; under 60 years, r = -0.20, p < 0.10). In general, the currently reported research has demonstrated that significant changes in laryngeal performance occur in response to advancing age. Individual differences in physiological integrity have been shown to influence the amount of vocal change observed in elderly subjects. These vocal changes have been shown to be sufficiently profound so as to significantly affect listeners' perceptions of the age of the speaker. SUMMARY It seems appropriate to indicate the direction in which our past research now leads us. We are planning a longitudinal study involving 200 elderly male subjects to further investigate the influence of the subjects' physiological status on their phonatory and auditory performances. Subject evaluations will be conducted at three different times throughout the course of the investigation. The research protocol will include comprehensive physiological and biochemical evaluations along with state-ofthe-art voice acoustic and auditory assessments. Those aspects of subject performance to be sampled will include (1) measures of voice fundamental frequency, duration, intensity, jitter and shimmer, harmonics/noise ratios, and listener perceptions of vocal quality; (2) measures of auditory sensitivity, discrimination, and acoustic immittance; and (3) measures of hemodynamic, pulmonary, metabolic, and biochemical function. Relationships among these variables will be probed through univariate Journal of Voice, Vol. 1, No. 1, 1987

and multivariate statistical approaches. A special feature of this study will allow for the classification of subjects in accordance with a fitness criterion which precludes the necessity of excluding elderly subjects who are unable to participate in the exercise tests frequently required for determination of physical fitness. By taking into consideration physiological status in addition to chronological age, groups will be defined more appropriately, thus reducing intragroup variability and increasing our ability to detect important changes in auditory and acoustic performance that Occur in senescence. We anticipate that this study will contribute to the normative base on senescent changes of voice and will serve to clarify the relationship of such changes to general and certain specific aspects of health status. The longitudinal nature of the study will provide information whereby the extent to which changes in laryngeal function can be predicted by measures of physiological status. Better knowledge of the normative aspects of aging and of the impact of degenerative processes on communicative processes will also facilitate a deeper understanding of the basic mechanisms that underly control of the laryngeal mechanism. REFERENCES 1. Hirano M, Kurita S, Nakashima T. Growth, development and aging of human vocal folds. In: Bless DM, Abbs JH, eds. Vocal fold physiology. Contemporary research and clinical issues. San Diego, CA: College Hill Press, 1983. 2. Kahane JC. A survey of age-related changes in the connective tissues of the human adult larynx. In: Bless DM, Abbs JH, eds. Vocal fold physiology. Contemporary research and clinical issues. San Diego, CA: College Hill Press, 1983. 3. Segre R. Senescence of the voice. Eye, Ear, Nose Throat Monthly 1971 ;50:223-33. 4. M c G e e r PL, McGeer EG. Aging and neurotransmitter systems. In Finch CE, Potter DE, Kenny AD, eds., Parkinson's disease, Vol 2, Aging and endocrine relationships. New York: Plenum, 1986:41-58. 5. Wagman I, Lesse N. Maximum conduction velocities of motor fibres of ulnar nerve in human subjects of various ages and sizes. J Neurophys 1952;15:235-44. 6. Wilcox KA, Horii YH. Age and changes in vocal jitter. J Gerontol 1980;35:194-8. 7. Mysak ED. Pitch and duration characteristics of older males. J Speech Hear Res 1959;2:46-54. 8. Ptacek PH, Sander EK, Maloney WH, Jackson CR. Phonatory and related changes with advancing age. J Speech Hear Res 1966;9:353-60. 9. Kreul E. Neuromuscular control examination for parkinsonism: Vowel prolongations and diadochokinetic and reading rates. J Speech Hear Res 1972;15:72-83. 10. Kent RD, Burkard R. Changes in the acoustic correlates of speech production. In Beasley DS, Davis GA, eds. Aging communication processes and disorders. New York: Grune & Stratton, 1981.

VOCAL INDICES OF BIOLOGICAL AGE 11. Hodkinson HM. Common symptoms o f disease in the elderly. Oxford: Blackwell, 1982. 12. Shipp T, Hollien H. Perception of the aging male voice. J Speech Hear Res 1969;13:703-10. 13. Finch CE, Schneider EL. Handbook o f the biology of aging. New York: Van Nostrand Reinhold, 1985. 14. Spirduso WW. Physical fitness in relation to motor aging. In: Mortimer JA, Pirozzolo FJ, Maletta GJ, eds. The aging motor system. New York: Praeger Publishers, 1982. 15. Fries JF, Crapo LM. Vitality and aging. San Francisco: Freeman, 1981. 16. Benjamin H. Biologic versus chronologic age. J Gerontol 1949;2:217-27. 17. Comfort A. Test battery to measure aging rate in man. Lancet 1969;27:1411-5. 18. Borkan GA, Norris AH. Assessment of biological age using a profile of physical parameters. J Gerontol 1980;35:177-84. 19. Ramig LA, Ringel RL. Effect of physiological aging on selected acoustic characteristics of voice. J Speech Hear Res 1983 ;26:22-30. 20. Chodzko-Zajko WJ, Ringel RL, O'Connor PJ. Cardiovascular and pulmonary performance and sensory deterioration in aging. Gerontologist 1985;25:215. 21. Offenbach SI, Chodzko-Zajko WJ, Ringel RL. Relationship between age, physiological status and cognition. Psychonomic Soc Bull 1986;24:350A.

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22. Darby JK. Speech evaluation in medicine. New York: Grune & Stratton, 1981. 23. Aronson AE. Clinical voice disorders. New York: Thieme Inc., 1985. 24. Weg JG. Chronic noninfectious parenchymal diseases. In: Guenter CA, Welch MH, eds. Pulmonary medicine. Philadelphia: J. B. Lippincott Co., 1977:513-56. 25. Jacobs DR, Schuker B. Type A behavior pattern, speech, and coronary heart disease. In: Darby JK, ed. Speech evaluation in medicine. New York: Grune & Stratton, 1981. 26. Taylor CB. The nature of stress: In: Darby JK, ed. Speech evaluation in medicine. New York: Grune & Stratton, 1981. 27. Walton JH. Brain diseases o f the nervous system. Oxford: University Press, 1977. 28. Rarnig LA. Effect of physiological aging on vowel spectral noise. J Gerontol 1983;38:223-5. 29. Titze IR. Parameterization of the glottal area, glottal flow and vocal fold contact area. J Acoust Soc Am 1984;75:57080. 30. Chodzko-Zajko W J, Ringel RL. The measurement and evaluation of physiological fitness in an elderly population, Exp Gerontol (in press). 31. Allen GD. Acoustic level and vocal effort as cues for the loudness of speech. J Acoust Soc A m 1971 ;49:1831-41. 32. Allen GD. Linguistic experience modifies lexical stress perception. J Child Language 1983;10:535-49.

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