The sound of senescence

Journal of Voice

Vol. 10, No. 2, pp. 190-200 © 1996 Lippincott-Raven Publishers, Philadelphia

The Sound of Senescence Sue Ellen Linville Department of Speech Pathology and Audiology, Marquette University, Milwaukee, Wisconsin, U.S.A.

Summary: This paper draws together findings of recent studies examining changes in voice with aging. Listeners' accuracy in perceiving age from voice is discussed, along with changes in speaking fundamental frequency, fundamental frequency stability, temporal aspects of speech, and resonance features of voice with aging. Descriptions are provided of differences in glottal gap configuration as a function of age and gender. In addition, acoustic/temporal measures that have been demonstrated to correlate with perceived age estimates are presented. Key Words: Vocal aging--Perceiving age from voice-Changes in voice with aging.

LISTENERS' PERCEPTION OF AGE FROM VOICE

Over the years, much time and energy has been devoted to studying the changes in voice that occur normally as individuals age. The question of interest to researchers has been "what are the vocal characteristics that result in speakers sounding old"? It is the intent of this paper to shed some light on this question by tying together some recent research examining age-related changes in voice. First, current knowledge related to perceptual aspects of vocal age will be examined: (a) listeners' accuracy at judging age from samples of voice, and (b) the features of voice and speech listeners have reported using to judge the age of a speaker. Next, age-related acoustic changes in voice and physiological changes in the larynx are detailed, followed by changes in the temporal aspects of speech with aging. As each of these aspects of aging voice is presented, an attempt is made to refer back to the issue of perceived age in order to associate actual age changes with perceived age estimates.

It has been established that listeners are capable of making reasonably good estimates of speaker age from taped voice samples (1-5). In Table 1, accuracy rates from several different studies are presented. The judges' task in these studies varied. They may have been asked to judge age from reading samples played forward (1,2,4), reading samples played backward (1), phonated vowels (I,5), or whispered vowels (5). Judges may have been asked to divide speakers into two age groups (1) or three age groups (5), or to make direct age estimates (2,4). As less acoustic information was present in the sample and the task became harder, accuracy rates dropped, as might be expected. However, listeners appear to be capable of judging age accurately at better-than-chance levels even with minimal acoustic cues such as are provided by whispered vowels. Of course, it should be pointed out that accuracy rates from whispered vowels are not astoundingly good. It should be noted, as well, that accuracy of perceived age estimates has been reported to vary as a function of listener age (6-8). In addition, it has been suggested that women may be more accurate than men in estimating speaker age from voice (9). Occasionally, in talkers unambiguously judged as old, listeners have been asked to describe the vocal

Address correspondence and reprint requests to Dr. Sue Ellen Linville at Department of Speech Pathology and Audiology, Marquette University, 619 North 16th Street, Milwaukee, W1 53233, U.S.A. This paper was presented at the Twenty-Third Symposium: Care of the Professional Voice, June 1994, at the Warwick Hotel, Philadelphia, Pennsylvania, U.S.A.

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S O U N D OF S E N E S C E N C E characteristics that these individuals display (3,9). Voice features considered characteristic of " o l d " voices included lower vocal pitch (regardless of speaker gender), increased harshness or hoarseness, increased strain, higher incidence of voice breaks, vocal tremor, increased breathiness, and reduced loudness, Older speakers also were perceived as demonstrating a slower rate of speech, greater hesitancy, less precise articulation, and longer duration of pauses, It is of interest that these features don't always correspond to actual acoustic changes in voice with aging, as will be evident shortly. In addition, these features don't always agree with data obtained from studies in which acoustic features actually were correlated with perceived age estimates (5,10).

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ACOUSTIC CHANGES IN VOICE WITH AGING Speaking fundamental frequency Speaking fundamental frequency (SFF) has been documented to change from young adulthood to old age in both men and women. The pattern of the change is different for the two groups, however. In Fig. 1, data on SFF from a number of studies have been plotted as a function of speaker age for male speakers (11-15). In mean, SFF lowers from young adulthood into middle age and then rises again into old age. By age 85, therefore, a man's SFF presumably would rise to the highest level of his adult life. The cause of the pitch drop observed in male speakers from young adulthood to middle age is unclear, although it has been speculated that the decline in pitch may be due to subclinical trauma associated with normal vocal use (13). A rise in SFF with advanced age would be predicted given anatomical and physiological changes in the larynx that occur with aging (16-19). Specificall3/, atrophy of muscle TABLE 1. Accuracy of listeners' age estimates from a variety of speech stimuli

Listening task Read: forward Read: backward Vowels: phonate Vowels: whisper

Relative age Young/rniddle~ Young/old age/old 99%° 87% 78% 51% a 43%

o Ptacek :and Sander, 1966(2). b Shipp and Hollien, 1969 (5). c Ryan and Capadan0, 1978(4). a Linville and Fisher, 1985(1).

Directage (r) .88b,.93%90

100

90 20

30

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40

50

60

I

70

80

90

100

Age in Years FIG. 1. Speakingfundamental frequency as a function of age in men,

tissue and/or increased stiffness of vocal cord tissue could be responsible for such a change. In women, the pattern is quite different. In Fig. 2, data from nonsmokers (20) is plotted separately. from data including both smokers and nonsmokers (14,21-23). In women, SFF appears to remain fairly constant until menopause when a drop in fundamental frequency (F0) occurs. Presumably, this drop in F0 is the result of hormonal changes during menopause resulting in vocal cord edema (19). The pattern is the same for smokers as for nonsmokers; smoking appears simply to lower F0 for speakers across age levels. With advanced age, F o remains fairly constant in women. Although some researchers have reported a slight tendency for Fo to rise with very advanced age in w o m e n (14,24), such increases have not been statistically simaificant and therefore must be considered "insubstantial. It is noteworthy, as well, that longitudinal studies suggest that the magnitude of the drop in F0 after mid~ die age in women may b e greaterthan what is sug" gested by the cross-sectional data presented here (25,26).

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Correlations of SFF with perceived age estimates correspond with changes in SFF that occur with chronological age. In other words, women tend to be perceived as older if their SFF is lower, at least in sustained vowel productions (1). Men, on the other hand, tend to be perceived as older if their SFF is higher (I0). However, differences in SFF between men perceived as young and men perceived as middle-aged have not been found to be statistically significant (10). This finding suggests that categories of "perceived young" and "perceived middle-aged" in men must be distinguished by acoustic information other than SFF alone. It should be noted, also, that correlations of SFF with perceived age don't correspond entirely with listener reports of reactions to SFF when judging age. That is, listeners have reported responding to lower pitch in both men and women as an indicator of more advanced age (2), despite the fact that higher SFF values in male speakers actually correlate with older age estimations (10). This finding suggests there may be some stereotyping by listeners regarding SFF and age.

Age in Years Smoking/Nonsmoking + Nonsmoking FIG. 2. Speakingfundamental frequencyas a function of age in women. Researchers have suggested recently that professional singers may demonstrate higher SFF levels than nonsingers (11). However, smoking histories of all subjects were not reported in that study. Without definitive knowledge that all the nonsingers also were nonsmokers, a conclusion that a history of professional singing results in higher SFF levels would be premature. SFF appears to be a very powerful and resilient cue to perceived age, as evidenced by the fact that listeners have significantly higher accuracy rates when judging age from phonated vowels as opposed to whispered vowels (1,27). In addition, listeners appear to ignore resonance cues that are available in the acoustic signal if Fo cues are also available. That is, mean Fo correlates with listeners' judgments of age from phonated vowel segments, whereas formant information, which also is available in the acoustic signal, does not correlate with age estimates. However, if Fo information is unavailable in the signal, as in the case of whispered vowels, formant frequency measures do correlate with age estimates (1). Journal of Voice, Vol. 10, No. 2, 1996

Stability of F o and amplitude Stability of vocal cord vibration has been examined as an aspect of vocal aging because such measures are felt to reflect voice control and regulation. It is assumed that increased age might bring about decrement of function that would result in increased instability of vocal cord vibration. Age-related changes in the larynx that might contribute to instability of vocal cord vibration include degeneration of muscle and connective tissue (16-19) and ossification/calcification of cartilages (28-3 I). Similarly, changes in the respiratory system also might be a factor in increased instability of vocal cord vibration with aging. Diminished elastic recoil of lung tissue (32-36) and reductions in vital capacity (34, 37-39) have been identified as occurring normally with advanced age. Reports from listeners regarding vocal cues that they felt marked old speakers also would suggest that old speakers demonstrate more instability in F 0 and amplitude than young speakers. Increased harshness and hoarseness in elderly speakers might suggest higher jitter and shimmer levels, whereas increased vocal tremor might suggest higher Fo standard deviation (SD) or amplitude SD (Amp SD) values in the elderly. Similarly, reports of a higher incidence of pitch breaks might reflect greater F0 instability.

SOUND OF SENESCENCE Jitter and shimmer Measures of stability of vocal cord vibration fall into two groups: (a) measures that reflect small, cycle-to-cycle fluctuations in vocal cord vibration; and (b) measures that reflect more gross fluctuations over time. Jitter is a measure of cycle-to-cycle fluctuations in the fundamental period of vocal cord vibration, whereas shimmer reflects cycle-to-cycle variation in waveform amplitude. We are not yet at a point that we can definitively state what changes occur in jitter and shimmer levels with aging. Recent studies have uncovered numerous factors that can interfere with valid and reliable cycle-to-cycle perturbation measurement, particularly in female voices (40-42). These methodological factors include mean sound pressure level (SPL) of phonation (40), mean F 0 of phonation (41), and analysis system differences (42). Because of these issues, findings of earlier studies examining age-related differences in jitter and shimmer need to be interpreted cautiously. However, some recent data on jitter and shimmer changes with aging in male speakers may provide some clue as to age-related differences in these measures. It appears from the data in Table 2 that elderly men as a group display higher jitter and shimmer values than do young men (43). These data also suggest that elderly men demonstrate considerably more variability in jitter and shimmer measures than do young men. Increased variability in elderly individuals is a consistent finding across many studies examining age-related differences in both acoustic and physiological measures (1,28,4347). Many factors related to individual health and fitness appear to contribute to this increased variability. In fact, once health and fitness issues are taken into consideration, differences in jitter with age may tend to be eliminated (43,45), whereas shimmer differences tend to remain (43).

T A B L E 2. Jitter and shimmer values f o r two age

groups o f men during production o f sustained /a/ vowels

Young Mean Range Old Mean Range

Jitter (%)

Shimmer (dB)

0.461 0.408--0.590

0.707 0.542-0.956

0.728 0.468--1.229

1.087 0.860-1.727

Data are from Orlikoff, 1990 (43).

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T A B L E 3. Fundamental frequency standard deviation values f o r three age groups o f men and women during sustained vowel productions

Young Mean Range Middle Mean Range Old Mean Range

Men a

Women b

1.06 0.69-2.37

1.47 0.84--2.39

No data

1.68 1.08-2.69

2.28 0.99-3.44

2.52 1.06--8.05

a Data are from Orlikoff, 1990 (43). h Data are from Linville and Fisher, 1985 (1).

F o SD and amplitude SD F 0 SD and Amp SD are measures of stability that reflect more gross fluctuations over time. These measures also tend to increase with increasing age (1,43). In fact, data from both men and women suggest that F 0 SD measures might be a better discriminator of vocal age than jitter (1,43). Some data on F0 SD values in men and women of varying ages during production of vowels sustained as steadily as possible are presented in Table 3 (1,43). Substantial differences can be seen between young and elderly speakers with regard to F 0 SD. In men, F0 SD more than doubled from young adulthood to old age. In women, F 0 SD increased by 71% over a similar period. It is also noteworthy that, for both men and women, the ranges of F 0 SD values did not overlap completely for young and elderly speakers. This finding contrasts with jitter measures where increased variability with aging has been observed to be particularly pronounced, especially in women (1).

Relationship of F 0 amplitude stability measures to perceived age Perceptually, jitter and shimmer have been found to be acoustic correlates of a voice quality referred to as rough, harsh, or hoarse, at least in pathological voices (47,48). That is, voices with very high levels of jitter and/or shimmer would be perceived by listeners as rough. It is of interest that there is evidence that jitter is not associated with perceived age in women (1). That is, women's voices with higher levels of jitter have not tended to be perceived as older by listeners, even if their jitter levels were considerable higher than values considered characteristic of normal voices. If jitter levels reJournal of Voice, Vol. 10, No. 2, 1996

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flect perceived roughness, then this evidence suggests that vocal roughness is not a particularly salient cue to vocal age in women. However, it is possible that shimmer is a more sensitive indicator of perceived roughness than jitter. In addition, there is evidence that the perceptual effects of jitter and shimmer are additive (47,49). Therefore, a definitive conclusion as to the significance of roughness as a perceptual marker of perceived age awaits further study. There is evidence that F0 SD is significantly associated with perceived age in women. Specifically, higher F 0 SD values in women's voices are associated with oidel age estimates by listeners (1). Similarly, F 0 SD has been shown to be significantly higher in men perceived as old, in comparison with men perceived as young (I0). It appears, therefore, that listeners may respond to F o SD differences when judging age from voices of both men and women. Just what is the perceptual phenomenon that listeners are responding to when Fo SD values are high? How might that phenomenon be different from perceived roughness, associated with high jitter/shimmer values? One possibility is that listeners are responding to relatively long-term, systematic variations in frequency, as opposed to random, cycle-to-cycle variations in frequency (I). Segments perceived as old might display progressive increases in frequency followed by progressive decreases. Such a segment might be heard as tremulous or "wobbling" (I). VOCAL CORD CLOSURE CHANGES WITH AGING Vocal cord closure assessed from visual examination An increase in the incidence of glottal gaps with aging might be predicted as a result of age-related changes in the laryngeal mechanism. Specifically, changes such as atrophy of the intrinsic laryngeal musculature or atrophy of connective tissue (16-19) might result in glottal gaps. The configuration of the glottal gaps observed with aging might be expected to vary as a function of the muscles affected. Weakening of the thyroarytenoid might result in incomplete closure from the vocal processes to the anterior commissure, or a spindle configuration. Weakness of the interarytenoids would result in posterior chink. Generalized weakening of adductor muscles may produce incomplete closure along the length of the glottis. Journal of Voice, Vol. 10, No. 2, 1996

As seen in Fig. 3, a high incidence of glottal gaps has been reported both in elderly men and elderly women from visual inspection of the larynx with use of either indirect laryngoscopy or videostroboscopy (22,46,50-53). The aging pattern for men is what one might predict given anatomical and physiological changes with aging. Young men display a fairly low incidence of glottal gap, with estimates ranging from 20 to 38% (51,52). Elderly men, on the other hand, display a significantly higher incidence of glottal gap. One study involving a fairly small number of speakers placed the incidence of glottal gap in elderly men at 67% (22). An increased incidence in glottal gap in elderly men might be predicted given reports of atrophy of laryngeal muscles in aged speakers (16,31). Although the cause of muscle atrophy in the elderly larynx has yet to be determined, it is possible that wear and tear factors contribute to muscle weakening. A more interesting pattern is seen in the data for women (Fig. 3). Both young and elderly women demonstrate glottal gaps frequently and these two groups do not appear to differ significantly in overall incidence. In young women, glottal gaps have 100 i I

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Elderly

RELATIVE AGE Men

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FIG. 3. Incidence of glottal gap in men and w o m e n at different age levels.

SOUND OF SENESCENCE

been reported in 70-95% of observations (46,5053), whereas in elderly women the incidence ranges from 58 to 90% (22,46,50). There is evidence, however, that young and elderly women do display differences in the configuration of the gaps observed and in the phonatory conditions under which gaps are observed. The data in Table 4 are from a study of 10 young and 10 elderly women (46). These data indicate that elderly women actually achieved complete closure more frequently than did young women. Anterior gap was the most commonly observed gap in elderly women, with a spindle shape also occurring significantly more frequently in elderly women. In young women, posterior chink was the most frequently occurring gap, supporting findings of earlier studies (50,52,54). The young women also demonstrated incomplete closure significantly more frequently than did elderly women, although rarely demonstrating anterior gap or a spindle-shaped glottis. The difference in incidence of posterior chink in young and elderly women is evident in Table 4. It is surprising that young women would demonstrate a higher incidence of posterior chink than would elderly women, given what is known concerning anatomical changes in the larynx with aging. Agerelated anatomical changes such as atrophy of muscle and connective tissue would work against closure of the posterior glottis rather than promote increased closure. Edema, on the other hand, might increase glottal closure. However, medical examination of videostroboscopic images revealed no apparent evidence of edema in any subject. Although a definitive explanation for this finding is not possible, some speculation as to possible explanations has been entertained. First, it is possible that some as yet undiscovered age-related alteration in the larynx supraglottally altered the superior view of the

T A B L E 4. Incidence o f various glottal configurations (%) f o r young and elderly women across nine pitch and loudness conditions

Complete closure Posterior chink Incomplete closure Anterior-posterior gap Anterior gap Spindle Irregular

Young women (n = 10)

Elderly women (n = 10)

17 42 18 19 2 0 I

26 13 5 II 27 Il 7

Data are from Linville, 1992 (46).

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posterior larynx. There is some evidence that a portion of the posterior glottis remains unclosed normally during vocal cord adduction (46). It is also possible that young women are physiologically capable of achieving vocal cord closure but fail to do so for functional reasons. Perhaps this adjustment is an economy measure or a means to achieve a desired voice quality such as breathiness. This adjustment, then, would be abandoned in elderly women as gaps in the anterior glottis begin to appear. Whereas this explanation also is speculative, there is evidence that young women display a significantly greater degree of perceived breathiness than do young men (52). No data are currently available on differences in perceived breathiness in young adult women and elderly women. Young and elderly women also differed in the incidence of posterior chink across loudness levels (46). In young women, posterior chink occurred fairly frequently across all loudness levels, whereas in elderly women posterior chink appeared to be particularly rare during loud phonation. It is possible that elderly women, upon experiencing agerelated glottal gaps more anteriorly in the glottis, need to close the posterior glottis in order to phonate loudly. Young women, on the other hand, having the advantage of full muscular capability anteriorly, might be able to keep the posterior glottis open and still achieve adequate loudness (46). Some support for this hypothesis comes from another study in which a correlation was noted between bowing of the vocal cords and maximum intensity of phonation in glottal gap (44). Vocal cord closure inferred from aerodynamic and electroglottography (EGG) measures Inverse-filtered air flow waveforms provide an estimate of the pattern of air flow through the glottis during consecutive vocal cord vibrations (55,56). One of the measures that can be derived from inverse-filtered air flow waveforms is air flow duty cycle, which is defined as the ratio of the time above a set baseline divided by the glottal period (57). Similarly, EGG duty cycle can be derived from EGG waveforms and represents the ratio of the time above a set baseline to the glottal period (57). Duty cycle measures are associated with less vocal cord contact and a shorter period of contact. That is, increased duty cycle equals decreased vocal cord contact and shorter time period of contact (5861). Journal of Voice, Vol. 10, No. 2, 1996

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Possible implications of vocal cord closure changes for the speaker An increased incidence of glottal gaps in elderly speakers, particularly elderly men, may result in use of increased laryngeal adductory forces to compensate for the closure deficit (57). Such an adjustment may be perceived by listeners as strained voice quality. It is of interest that significantly higher estimated subglottal pressure values have been reported for elderly male speakers, in comparison with young men (57). Such an increase in subglottal pressure may be indicative of vocal cord stiffening (62). Fewer syllables per breath group also could be a consequence of vocal cord closure changes with aging. Data have been gathered indicating that elderly men and women require more intrasentence breaths than do their younger counterparts (63). There also are data indicating that maximum phonation time in both men and women is reduced with aging (64,65). Maximum phonation time in elderly women has been associated both with measures of vocal intensity and with pitch range measures (44). This finding suggests that both laryngeal valving factors and respiratory control factors are operating in elderly

When air flow and EGG duty cycle measures were obtained on men and women of varying ages, interesting age-related patterns emerged, particularly in women (57). As shown in Table 5, with the exception of EGG duty cycle in the high-pitch condition, elderly men demonstrated longer duty cycles than did young men, indicating less complete vocal cord closure for men with aging. This pattern is expected given what is known about anatomical changes in the larynx with aging (16-19,22). However, duty cycle measurements in women decreased slightly with age (Table 5), suggesting slightly increased vocal cord contact and increased time of contact in elderly women. This pattern would not be predicted given age-related changes in the larynx with aging. However, these findings do correspond with findings of stroboscopic studies (46,50-53) and provide further evidence that elderly women do not display a higher incidence of glottal gaps than do young women. In fact, elderly women may tend to close the glottis more completely than would young women. It is possible that this agerelated pattern in women is associated with a shift from a larger posterior gap in the young adult years to a smaller anterior gap with advanced age.

T A B L E 5. Group means (M) and standard deviations ( S D ) f o r airflow duty cycle and electroglottograph duty cycle

obtained during/btep/and ~re~productions across four conditions Air flow duty cycle (%) Women

Men

Elderly Condition Syllable ([b~ep)] production Normal Soft Loud High Vowel ([ae]) prolongation Normal Soft Loud High

Young

Elderly

Young

M

SD

M

SD

M

SD

M

SD

57.75 63.88 53.12 66.71

6.50 6.28 8.78 3.72

60.21 66.66 57.02 69.28

8.32 8.54 7.71 4.92

62.80 68.68 61.02 63.42

9.84 10.92 8.47 9.47

51.94 57.36 49.32 58.64

6.40 5.72 4.19 10.26

59.11 65.89 58.09 67.34

6.73 4.27 10.50 5.87

63.00 69.34 61.93 73.49

9.71 5.33 10.33 6.00

62.23 65.67 62.65 63.53

9.08 9.24 9.75 9.98

56.99 61.94 49.71 61.89

10.65 7.39 6.20 10.20

Electroglottograph duty cycle (%) Syllable ([baep]) production Normal Soft Loud High Vowel ([ae]) prolongation Normal Soft Loud High

47.73 52.19 45.26 54.29

6.91 5.21 6.72 9.01

52.38 53.10 50.93 57.51

5.44 6.64 4.22 5.96

54.47 57.49 51.01 50.15

6.06 7.27 6.05 7.31

46.65 52.82 45.27 51.99

4.62 5.29 5.19 8.88

48.20 54.52 43.64 55.56

5.52 6.87 4.83 10.42

53.92 56.41 55.00 62.28

5.46 9.25 6.78 6.90

54.80 59.17 50.35 48.50

5.64 6.50 7.98 9.27

48.26 52.44 45.96 50.90

5.14 6.05 5.05 10.77

Data are from Higgins and Saxman, 1991 (57). (Reprinted by permission of the American Speech-Language-Heating Association.)

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women to reduce the duration of time elderly women can phonate. Respiratory factors also may be involved in findings of reduced maximum phonation time. Both decreased vital capacity and decreased maximum expiratory flow rate have been reported in elderly speakers (34,63,66--68). CHANGES IN VOCAL RESONANCE WITH AGING Changes in vocal resonance also have been investigated as a function of speaker age (1,69,70). Such changes might be predicted given the substantial evidence that has been gathered on changes in the supraglottic vocal tract from young adulthood to old age. Such changes include 3-5% growth of the facial skeleton (71-73), atrophy/hypertrophy of tongue musculature (74-76), tooth loss (77), weakening/ atrophy of pharyngeal musculature (78), and restricted movement of the temporomandibular joint (79). It also has been hypothesized that elderly speakers may systematically alter their articulatory positioning and in so doing alter the resonance characteristics of their speech (70). Thus, speakers might learn an "elderly speech" pattern as the socially expected pattern (80). Studies examining vocal resonance changes with aging have been limited in number, and findings have been conflicting. A longitudinal study of four male and two female speakers over periods of up to 29 years indicated that the formant frequencies of seven vowels and two diphthongs from contentcontrolled running speech samples lowered with age in both men and women (81). These findings were supported in a later cross-sectional study looking at sustained /ae/ vowel productions of 75 women (1). In that study, F t frequencies from sustained/ae/vowel productions lowered significantly with aging in women. A more recent cross-sectional study investigated formant frequencies of five vowels from sustained vowel productions of 20 men and 20 women (70). Results suggested that elderly speakers may tend to centralize their tongue position during vowel production. Specifically, F~ frequencies for front and mid vowels were higher in elderly speakers than in young speakers. Ft frequencies for back vowels were lower for elderly speakers than for young speakers. Taken together, these studies suggest that resonance characteristics of voices do change with aging, although the precise nature of the change is

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open to some question. A pattern of consistent formant frequency lowering across all vowels might indicate vocal tract lengthening with aging. It has been hypothesized, although no data were reported, that the larynx may lower in the neck with advanced age as a result of stretching of ligaments and atrophy of the strap muscles of the neck (82). A pattern of variations in formant frequency change in different vowels might indicate variations in articulatory positioning with aging. More definitive conclusions regarding the nature and extent of resonance changes in voices with aging will follow studies directly relating vocal tract configurations to acoustic variables. In addition, a study looking at variations in long-time average speech spectra with aging might shed further light on the issue of agerelated changes in vocal tract resonance characteristics. Relationship of r e s o n a n c e m e a s u r e s to perceived age estimates

There are indications that vocal resonance characteristics can provide cues to listeners as to speaker age. Some association of formant frequency measurements to perceived age estimates from whispered vowels produced by women has been reported (1), although the perceptual significance of resonance cues appears to be limited. Resonance information is not correlated with perceived age estimates if F0 information is also available in the signal (1), at least when sustained vowel productions are used as stimuli. It is interesting to speculate as to the association of resonance information to perceptual age from running speech. Although no data are available currently to address this question, judges of speaker age did mention "imprecise articulation" as a feature of speech that marked speakers as elderly. CHANGES IN SPEECH RATE WITH AGING Slower speech rate in elderly speakers has been well documented (4,83-86). The following have been mentioned as possible explanations for the observed slowing of speech rate: neuromuscular slowing (83,86), changes in the respiratory system (87,88), physiological condition (88), increased cautiousness/expectations of society (84,85), and fatigue (13). It is interesting that slower reading rates in elderly speakers were found to be correlated with reductions in F o stability in one study (44). This finding might suggest that a generalized loss of Journal of Voice, Vol. 10, No. 2, 1996

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physiological control with aging is reflected both in slower reading rates and in greater F0 instability. Slower reading rates in elderly speakers also were found to be correlated with reductions in maximum intensity level (44), providing support for the notion that changes in the respiratory system with aging, and/or inadequate laryngeal valving with aging, result in slower reading rates. Reduced elastic recoil of lung tissue with aging (36,89,90) might result in difficulties producing loud speech and also affect an elderly individual's ability to maintain phonation for a long period without pausing to breathe. Inadequate laryngeal valving would result in excessive air escape during phonation, necessitating more frequent pauses and reducing maximum intensity level. Relationship of speech rate to perceived age estimates Slower speech rate has been associated with older perceived age estimates in male speakers (I0). Breath management factors also have been associated with perceived age estimates in men. Specifically, a larger number of breaths and longer breath pause durations were associated with older age estimates (10). SUMMARY Listeners are able to make reasonably good estimates of speaker age from voice samples. Speaking fundamental frequency, measures of F0 stability, temporal aspects of speech, and resonance features of voice have been found to vary as a function of speaker chronological age. Elderly men have been observed to have a significantly higher incidence of glottal gaps than do young men. Elderly women, on the other hand, do not demonstrate a significantly higher incidence of glottal gaps than do young women. Indeed, elderly women may tend to close the glottis more completely than young women. Acoustic/temporal measures that have been demonstrated to correlate with perceived age estimates by listeners include speaking fundamental frequency, fundamental frequency standard deviation, formant frequency measures from whispered vowel productions, and speech rate/breath management factors. REFERENCES 1. Linville SE, Fisher H. Acoustic characteristics of perceived versus actual vocal age in controlled phonation by adult females. J Acoust Soc A m 1985;78:40-8. Journal of Voice, Vol. 10, No. 2, 1996

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