A fundamental frequency investigation of children ages 6–10 years old

.I. COMMUN. DISORD. 22 (1989), 115-123

A FUNDAMENTAL FREQUENCY INVESTIGATION OF CHILDREN AGES 6-10 YEARS OLD DAVID N. SORENSON Department

of Speech

Pathology and Audiology,

Idaho State University, Pocatello

The fundamental frequency characteristics of 30 children between the ages of 6 and 10 years were investigated in a variety of speech tasks. The results indicated that average fundamental frequency across tasks for the boys is approximately 262 Hz, and for girls approximately 281 Hz. Statistical analysis indicated that there was no significant difference in the fundamental frequency of boys and girls in this age range. High vowels were found to have higher fundamental frequency values than low vowels. Sustained vowels had higher fundamental frequency values than either spontaneous speech or reading for both groups of speakers. The results of this investigation are discussed in terms of maturational processes, and in comparison to corresponding adult information.

INTRODUCTION Over the years much research effort has been spent in determining the fundamental frequency characteristics of preadolescent children. The results of this research, with few exceptions, indicate that prior to puberty there is no significant difference in the fundamental frequency characteristics of male and female children (Murphy, 1964; Luchsinger and Arnold, 1965; Kaplan, 1971). However, these studies are limited in that the data are based on a restricted set of tasks. Hasek, Singh, and Murry (1980) reviewed 24 studies of fundamental frequency of males and females in the age range 5-10 years. They found that 18 studies used either reading passages or repeated sentences. The remaining studies involved spontaneous speech (2), production of long vowers (3), or responses to pictures (1). In none of the 24 studies reviewed were subjects required to complete more than a single phonatory task. Fundamental frequency investigations of adult speakers indicate that there are substantial differences in fundamental frequency depending on the task used to elicit voice production. For instance, it is consistently Address correspondence to David N. Sorensen, Ph.D., Department of Speech Pathology and Audiology, Campus Box 8116, Idaho State University, Pocatello, ID 832094009. 0 1989 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010

115 0021~9924189/$3.50

116

D. N. SORENSEN

found that spontaneous speech yields the lowest fundamental frequency values and sustained vowel production yields the highest fundamental frequency values, with reading yielding values somewhere in between those two points. Furthermore, it has been noted that vowel height influences the fundamental frequency of a sustained vowel production (Peterson and Barney, 1952; House and Fairbanks, 1959; Lehiste and Peterson, 1961). Corresponding information for preadolescent speakers is conspicuously absent. The purpose of the present investigation was to study the fundamental frequency characteristics of a group of male and female preadolescent speakers as they participated in three phonatory tasks-sustained vowel production, spontaneous speech, and reading. Since the speakers produced a number of different vowel productions, it was possible to look at the effect that differing vowels have on fundamental frequency. The provision of this information will give us a greater understanding of the dynamics of voice production in the preadolescent. METHOD Subjects Three boys and three girls from each of the age levels 6, 7, 8, 9, and 10 years were selected as participants for this study. Female ages ranged from 6;l years to IO;5 years. Male subjects ranged in age from 6;3 years to 10;ll years. Individuals with a history of respiratory, laryngeal, language, and/or articulation problems were excluded from the subject population. In addition, potential subjects with hearing acuity poorer than 25 dB (ANSI, 1969) at 500, 1000, and 2000 Hz in either ear were screened out of the subject population since such alterations of auditory sensitivity are known to affect vocal fundamental frequency characteristics.

Recording Procedures and Phonatory Tasks Each subject was seated in a sound-treated booth and fitted with a headholder from which was suspended a condenser microphone (Sony AD38) on an adjustable arm. The microphone was placed so that it was 10 cm from the subject’s lips. The voice samples of the subject picked up by the microphone were recorded at a transport speed of 7.5 lps on a highquality tape recorder (Sony TC399) located oustide the booth. There were three different phonatory tasks: (1) Oral reading of factual prose in which the subjects were required to read two pages from a firstgrade level reader (Robinson, Monroe, and Artley, 1962): All subjects read the same two pages (pages 36 and 37). (2) Spontaneous speech in which the subjects were asked to talk about a picture placed in front of

CHILDREN’S

FUNDAMENTAL

FREQUENCY

VALUES

117

them: The picture selected for this task was W-3 from the Peabody Language Development Kit, Level 3. Subjects were instructed to talk for at least 30 seconds as timed by the examiner. (3) Sustained vowel production in which the subjects were asked to phonate the vowels /i, I, E, a, A, a, u/ for about 5 seconds as steadily as possible: Each vowel was repeated three times with rest periods between vowels, and between trials. The examiner explained and demonstrated each of the phonatory tasks. Subjects were given the opportunity to practice the tasks prior to recording. Demonstration and practice were essential in the sustained vowel productions in order to ensure that the desired vowel token was produced. The sustained vowel task was repeated until the examiner judged that three acceptable tokens of each vowel were produced. Acoustic Analysis Following the recording of the phonatory tasks, intensity x time tracings were made of the sustained vowel productions using a graphic level recorder (B&K Type 2305). By examining the intensity x time tracings, as well as by listening to the samples, the most stable production of each vowel for each subject was determined. From the midportion of the selected samples, a segment of approximately 3 seconds was chosen for further analysis. Measures of fundamental frequency were obtained using an automatic fundamental frequency analysis program (Horii, 1975, 1979, 1980). In this procedure the voice samples are digitized at the rate of 20000 times-persecond. Following sampling the computer program automatically analyzes the digitized data and outputs a fundamental frequency histogram and mean fundamental frequency values. RESULTS The results of this study are presented in terms of three separate analyses. In the first the fundamental frequency differences between the male and the female subjects are examined through a three-factor repeated-measures analysis of variance (sex-by-age-by-task) (Winer, 1971). In the second analysis, differences in the vowel task are examined to determine the pattern of fundamental frequency as a function of vowel production (vowel height). Finally, age-by-task differences are examined for male and female groups separately through a two-factor repeated measures analysis of variance. The average fundamental frequency of the male and female subjects at each of the five age levels are reported in Tables 1 and 2, respectively. A three-factor analysis of variance was performed to test for the main effects of sex, age, and phonatory task. The main effect of sex was found

Mean

10

9

8

274.60

280.26 (4.77) 303.78 (7.37) 262.82 (4.98) 273.25 (6.48) 252.89 (5.36)

6

7

/iI

Age

267.99

285.33 (17.32) 302.63 (7.06) 255.93 (10.86) 237.60 (11.14) 258.44 (15.47)

Ill

lael 253.43 (13.61) 273.29 (13.44) 252.77 (17.62) 230.55 (16.29) 246.38 (16.95) 251.28

258.71 (15.15) 291.89 (21.05) 255.82 (8.72) 236.06 (10.64) 248.67 (18.13)

258.39

284.81

298.69 (8.15) 310.22 (6.35) 270.99 (9.43) 271.03 (22.57) 273.12 (9.16)

lul

262.77

276.91 (18.35) 290.17 (10.54) 258.27 (13.72) 241.10 (29.29) 247.40 (17.65)

Id

258.06

263.70 (20.00) 302.82 (25.56) 256.61 (14.45) 228.00 (15.24) 239.15 (18.00)

la/

Values for the Boys in Each of the Three Phonatory

/El

Table 1. The Mean Fundamental Frequency Each Age Level are in Parentheses

241.99

250.81 (25.10) 288.04 (22.04) 229.35 (25.37) 221.45 (52.29) 220.31 (44.31)

Speech

254.42

255.86 (23.14) 292.72 (31.86) 239.21 (24.68) 236.81 (48.93) 247.54 (28.54)

Reading

Mean

for

261.59

248.21

241.76

253.53

295.06

269.30

Tasks. Standard Deviations

Mean

10

9

8

291.09

323.06 (5.21) 291.00 (6.12) 281.27 (4.84) 299.62 (5.39) 260.50 (4.24)

6

7

Ii/

Age

287.19

309.24 (20.01) 286.75 (11.14) 266.25 (9.90) 291.67 (12.08) 276.02 (16.59)

Ill

276.74

293.98 (9.66) 283.24 (21.54) 265.64 (20.23) 274.92 (11.11) 265.92 (16.19)

/El

Table 2. The Mean Fundamental Frequency Each Age Level are in Parentheses

297.73

272.79

Id

325.33 (6.72) 284.11 (9.02) 291.65 (7.70) 300.92 (15.34) 286.64 (6.21)

ICI

285.33

315.93 (9.14) 273.76 (14.47) 266.06 (17.76) 281.78 (16.29) 289.10 (11.08)

/Al

for the Girls in Each of the Three

286.18 (22.67) 276.70 (15.71) 265.45 (16.27) 268.90 (11.31) 266.71 (11.70)

Values

260.26

296.45 (36.89) 257.98 (38.24) 251.28 (30.19) 266.11 (38.53) 229.47 (40.59)

316.41 (34.03) 281.90 (19.02) 262.63 (15.58) 281.49 (6.43) 292.25 (20.79) 286.94

Speech

Tasks.

Id

Phonatory

214.74

281.42

269.32

283.38

267.59

278.85

307.98

305.20 (32.19) 274.12 (33.92) 258.08 (28.12) 279.07 (36.66) 257.23 (30.22)

for Mean

Deviations

Reading

Standard

120

D. N. SORENSEN

not to be significant (F = 2.37, & = 1, 20, p = .OS) indicating that the average fundamental frequency of female children aged six to ten was not significantly different from the average fundamental frequency of male children of the same age. The main effect of age was not significant (F = 1.08, & = 4, 20, p = .OS) either, indicating that the fundamental frequency values of the various age groups did not differ from each other. The main effect for task was not significant (F = 1.47, & = 8, 160, p = .05). This result indicated that, unlike adults where fundamental frequency is task dependent, there was no difference in the average fundamental frequency of spontaneous speech, oral reading, and sustained vowel production. There is an indication from previous research on adult fundamental frequency characteristics that vowel height may have an effect on a vowel’s inherent fundamental frequency. For this reason, the vowel task was visually inspected to determine if there were systematic variations in fundamental frequency as a function of vowel height. Examination of the group mean data from Table 1 indicates that the /i/ and the /u/ have the highest fundamental frequencies among the vowels. In fact, as the productions progress from /i/ to /aA there is a continual lowering of the fundamental frequency. The /A/ and /al have fundamental frequency values that are relatively close, followed by a large increase in fundamental frequency for the /u/. These trends are evident for both the male and the female subjects. Though the three-factor analysis of variance indicated that neither the main effect of age nor the sex-by-age interaction was significant, an examination of the data in Table 1 suggested that developmental trends for the two sexes may differ. For this reason, a second series of analyses of variance was performed. In these analyses male and female children were analyzed separately in a two-factor repeated measures analysis of variance (age-by-task) (Winer, 1971). For the male subjects the main effect of age was significant (F = 5.41, df = 4, 70, p < .OOl), indicating that the average fundamental frequency of at least two age groups differed significantly. This result was further analyzed with a Newman-Keuls test, which showed that the average fundamental frequency at ages 6 and 7 differed significantly from the average fundamental frequency which occurred at ages 8-10. The main effect of age for the female subjects was not significant (F = 3.45, Q!! = 4, 70, p > .Ol). These two results indicate that the male fundamental frequency lowers in the age range 6 to 7 years, then remains relatively stable. No such developmental trend is noted for the female children. The task main effect in both male (F = 7.68, & = 8, 80, p < .OOl) and female (F = 6.81, & = 8, 80, p < .OOl) analyses was significant, which indicated that spontaneous speech has a lower fundamental frequency than either reading or sustained vowel production.

CHILDREN’S

FUNDAMENTAL

FREQUENCY VALUES

121

DISCUSSION The present investigation was motivated by a desire to determine the differences in fundamental frequency in a group of children aged 6 to 10 years. Previous research on the fundamental frequency characteristics of this group has dealt with a single phonatory task, either sustained vowels or spontaneous speech. There is, however, a paucity of information on the fundamental frequency characteristics of children across tasks. In addition, this investigation provided an opportunity to reexamine the sexrelated and age-related differences in fundamental frequency in male and female children. The results of this research are in agreement with previous research that indicates no significant difference in the fundamental frequency of males and females in the age range 6-10 years (Eguchi and Hirsh, 1969; Fairbanks, Herbert, and Hammond, 1949; Fairbanks, Wiley, and Lassman, 1949; Van Oordt and Drost, 1963). Kent (1976) indicates that the average fundamental frequency of males and females in this age range is between 200 Hz and 325 Hz. The overall average fundamental frequency of the male and female subjects in the present investigation fell within that range. Hasek, Singh, and Murry (1980) found a systematic lowering of fundamental frequency in a similar age. The present investigation did not find a systematic lowering of the fundamental, although there was a tendency for the fundamental to drop. Previous research has also indicated that female speakers in this age range have a lower fundamental frequency than male speakers [see Wilson (1979) for a complete review of those studies]. The results of the present investigation do not confirm that observation. At ages 6,8,9, and 10, the male speakers have the lower fundamental frequency values, while at age 7, the female speakers have the lower fundamental frequency values. The analysis of variance of the male and female data demonstrated a near significant age effect. Further probing of this result in age-by-task analyses of variance for male and female groups separately indicates that there is a significant difference in the fundamental frequency at the various age levels for the males but not for the females. Explanations for this finding can only be speculative. Crelin (1973) conjectures that sex related changes in the larynx begin to appear as early as the third or fourth year. These structural modifications may be greater in the preadolescent male than the preadolescent female and may result in the age-related fundamental frequency lowering which was noted. It is also possible that there is a cultural factor involved, which encourages male children to assume a lower fundamental frequency. The highest fundamental frequency values were associated with the high vowels and the lowest fundamental frequency values with the low vowel /a/. Observations of this heightened fundamental frequency for high

122

D. N. SORENSEN

vowels has been previously noted for American English (Peterson and Barney, 1952; House and Fairbanks, 1953; Lehiste and Peterson, 1961). Lehiste (1970) notes that when the tongue is raised to produce a high vowel, the larynx tends to be pulled upwards and the laryngeal muscles stretched. This increases the tension in the vocal folds and causes an increase in their rate of vibration. Likewise, Lehiste and Peterson (l%l) found that among the cardinal vowels, ld had the lowest fundamental frequency. With the tongue in a lower position, tension in the laryngeal muscles is reduced, and the fundamental frequency is lowered. The results of this investigation indicate that, in the age range studied, there is no significant difference in the mean fundamental frequency of male and female preadolescents. Though there is no sex-related difference, it was noted that the male fundamental frequency lowers between ages 6 and 7, then stabilizes from 7 to 10 years. The female fundamental frequency, however, does not follow this pattern. The principal finding of this study relates to the across-task differences. Spontaneous speech and oral reading have the lowest fundamental frequency values, and sustained vowel productions have the highest fundamental frequency values. These task differences are the result of the physiological setting of the larynx. During sustained vowel production there is a greater and a constant tension in both the intrinsic and the extrinsic laryngeal muscles, which causes the vocal folds to vibrate at a higher rate. During oral reading and spontaneous speech the tension in the laryngeal muscles is reduced, resulting in lower fundamental frequency values. The fact that oral reading has a higher fundamental frequency than spontaneous speech would seem to indicate that oral reading sets laryngeal tension to a level somewhat higher than for spontaneous speech. This higher level of laryngeal tension is reflected in a slightly elevated fundamental frequency. This research was supported by a Biomedical Research Grant from the Department of Health and Human Services, Public Health Service. Portions of this paper were presented at the 1983 annual convention of the American Speech-Language and Hearing Association, Cincinnati. Special thanks is given to Dr. Yuki Horii, who provided the computer programs for the acoustic analysis.

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