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Maximum phonation time for children with normal voices
J. COMMUN. DISORD. 17(1984), 309-317
MAXIMUM PHONATION TIME FOR CHILDREN WITH NORMAL VOICES DENIS E. FINNEGAN Speech Pathology and Audiology Department James Madison University, Harrisonburg, Virginia
Maximum phonation time (MPT) data were collected for 286 male and female children between the ages 3-6 and 17-11. Subjects sustained phonation of the vowel /a/ for 14 consecutive trials. The influence of sex, age, and multiple trials on MPT was studied. The group mean MPT for the male subjects was significantly longer than for the female subjects. Generally, phonation time increased with age for both sexes. A definite monotonic increase in length of sustained phonation was not apparent across all age levels. Optimum MPT performance can be enhanced by using repeated trials, and by providing visual feedback and encouragement regarding depth of inhalation, verbal instructions and encouragement regarding increased phonation time, and visual feedback regarding length of sustained phonation prior to and during each trial. The large intra- and intersubject variability in MPT performance reported in this study prevents valid individual-group mean MPT comparisons. A more discriminatory clinical interpretation of MPT is necessary.
INTRODUCTION The present study was conducted to investigate the influence of sex, age, and multiple trials on maximum phonation time (MPT) for a large group of children with normal voices. For the purpose of this study, MPT was defined as the length of time that an individual could sustain an isolated vowel without the appearance of glottal fry or a substantial decrease in loudness (Launer, 1971). The measure of MPT reflected the mean of the three longest trials. Investigations of MPT for young children and adolescents have been numerous (McQueen and Saxman, 1970; Launer, 1971; Harris, 1971; Platt et al., 1975; Coombs, 1976; Lewis, 1977; Tait and Michel, 1977; Looney and Harden, 1980). Researchers agree that a wide range of variability exists in MPT both between and within children across trials. Children with normal voices produce longer phonation times than children with vocal pathologies, and children sustain certain vowels, such as /i/ for l2 set longer than others, such as /a/. Address correspondence to: Denis E. Finnegan, Ph.D., Speech Pathology and Audiology Department, New Education Building, James Madison University, Harrisonburg, VA 22807. 0 1984 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017
309 002 I-9924/84/$03.00
310
D. E. FINNEGAN
Conflicting results exist involving the influence of sex and age on MPT. Launer (1971), Harris (1971), Platt et al. (1975), and Lewis (1977) reported that males sustained phonation longer than females, while McQueen and Saxman (1970), Tait and Michel (1977), and Looney and Harden (1980) found that the main effect of sex was not significant. Launer (1971), Coombs (1976). and Tait and Michel (1977) indicated that phonation time tended to increase with age; however, a definite linear trend was not found. Conversely, Lewis (1977) demonstrated that age was not a significant factor in relation to phonation time. Lewis (1977) was the only investigator to study the influence of repeated trials on MPT for children. Subjects sustained production of la/ for 20 consecutive trials. Lewis found that only 2% of the children produced their longest phonation by the third trial. Lewis’ study was incomplete, however, because the influence of repeated trials was measured for only two different age groups. Normative MPT for children is important to serve as a valid indicator of phonatory function, Present normative data is both invalid and incomplete. Children were not allowed a sufficient number of trials to achieve their “maximum phonation,” and most investigators sampled an age range of fewer than 5 yr. The largest age range sampled in a single study was 9 yr (Launer, 1971). The methodology for measuring MPT must be revised, and the age range sampled must be expanded to provide valid and complete normative standards. These data can then be used as a meaningful measure for screening voice disorders in children. A refined methodology was devised and MPT was sampled across a 14.5yr range. The influence of sex, age, and repeated trials on length of phonation was investigated.
METHODS Subjects Subjects for the study came from northwestern Virginia. Fifteen schools were randomly selected from a total of 56 possible preschool, primary, and secondary schools within a three-county area. Five of the schools were preschool, seven were primary, and three were secondary. With the exception of the preschools, each school had between two and four different classes at each grade level. An equal number of children were selected randomly from each class, at each grade level, from each primary and secondary school. Data were collected for 286 children ranging in age from 3-6 to 17-l I. Ten male and ten female children were grouped at each 12-mo interval. All children were considered by their classroom teacher to be of normal intelligence and to be emotionally stable. Caucasian, Afro-American, and
MAXIMUM
PHONATION
TIME
311
Oriental children residing in urban and rural environments were included in the sample. Subjects represented low, middle, and upper income families. No child who was physically handicapped or currently enrolled in speech therapy was selected for inclusion in the study. All children were judged by the experimenter (a speech pathologist with 9 yr of experience) to have age-appropriate articulation, normal structure and function of the oral peripheral mechanism, a habitual pitch and modal loudness level appropriate for their age, sex, and body size, and fluent speech. In addition, all subjects passed a pure tone hearing screening. Procedure MPT data were recorded on an individual basis. All testing was conducted in a quiet, familiar room within each child’s school. The experimental task consisted of sustaining phonation of the vowel /a/ for 14 trials. Each phonation was tape recorded. Pitch was controlled through the repeated use of a carrier phrase preceding the production of the isolated vowel /a/. Children were instructed to say the carrier phrase, “I call my mother Ma,” in their normal voice. Then, they were instructed to repeat the phrase, prolonging the vowel in the final word for several seconds. Loudness was controlled by self-monitoring the needle indicator deflection on the VU meter of the tape recorder. Each child was instructed to maintain a zero reading as he/she prolonged the /a/ vowel. Immediately prior to each trial, subjects were instructed to visually monitor their inhalation by inhaling through the plastic connection tube in the Triflo II - Incentive Deep-Breathing Exerciser (Chesebrough Ponds, Inc., model 5-7173). Visual feedback provided by the Triflo II motivated the children to inhale maximally before each phonation. Immediately following inhalation, subjects were instructed to sustain the vowel /a/ for as long as possible, using the previous carrier phrase as a reference point for maintaining a habitual pitch level. Subjects received visual feedback regarding the duration of phonation continuously by self-monitoring on a digital readout device (Coulbourn Electronic Counter, model R 11-25). They were encouraged to increase the duration on the succeeding trial. A 30-set rest period was inserted between each trial. No child was recorded following participation in a vigorous physical activity, such as gym, band, or recess. A stop watch was used to measure phonation time live voice. Following data collection, the tape recorded production of each child’s phonation was played into a graphic-level recorder (General Radio model 1521-B) to produce a permanent record and to provide a graphic indication of the rise and fall of intensity, hence, the onset and cessation of phonation time. Measurements of MPT produced by each subject were also obtained from this record.
312
D. E. FINNEGAN
RESULTS Intrajudge reliability of measuring MPT using the stop watch was completed 12 wk following data collection for a random sample of 25 children. The correlation between the two stopwatch measurements was statistically significant (r = +0.96; t(23) = 3.06; p < 0.01). All live stop watch measurements were compared with their countermeasurements derived from the graphic-level recorder. The two measurements were highly related (r = +0.89; ~(285) = 15.06; p < 0.01). The mean and standard deviation of the three longest sustained phonations, measured in seconds and categorized according to sex and age level, are presented in Table 1. The group mean of the three longest sustained phonations for the male children was 18.23 set; the total sample standard deviation was 7.20 set, and 15.79 and 5.72 set, respectively, for the female children. The group mean MPT for the males was significantly longer than for the females [t(284) = 3.26; p < 0.011. Males phonated longer than females in 12 of 15 age groups. The only age levels where females sustained phonation longer than males were: 5-O to 5-1 I, 8-O to 8-11, and 16-O to 16-11. The mean of the three longest phonations for males increased from 7.92 set for the 3.5-yr-olds to 28.70 set for the 17.5-yr-olds, and those for the females increased from 6.28 set for the 3.5-yr-olds to 21.99 set for the 17.5-yr-olds. A definite monotonic increase in length of sustained phonation was not apparent across all age levels for either sex. Table 1. Mean and SD of the Three Longest in Seconds (n = 286)
Sustained
Phonations
Female subjects Age 3-6 to 4-oto 5-o to 6-Oto 7-o to 8-O to 9-o to 10-O to II-0 to 12-o to 13-o to 14.0 to 15-O to 16-O to 17-O to
3-11 4-11 5-11 6-11 7-11 8-11 9-11 IO-1 I 11-11 12-11 13-t I 14-11 15-11 16-I 1 17-11
Grouo totals
n
Measured
Male subjects M
SD
5 10 10 9 9 IO 10 10 IO 9 10 10 10 10 10
7.92 9.99 10.12 13.90 14.63 16.81 16.83 22.20 19.85 20.23 22.34 22.34 20.74 21.04 28.70
1.81 2.51 3.05 2.98 2.82 4.51 6.07 4.74 3.79 5.72 8.19 6.89 5.32 4.40 7.08
142
18.23
7.20
M
SD
n
5 10 IO 9 10 10 10 10 10 10 10 10 10 10 10
6.28 8.86 10.47 13.81 13.68 17.12 14.47 15.88 14.76 15.16 19.24 18.85 19.53 21.85 21.99
1.76 1.84 2.57 3.65 2.45 4.62 3.78 5.99 2.06 3.87 4.58 5.15 4.66 4.47 6.30
144
15.79
5.72
MAXIMUM
PHONATION
TIME
313
Ninety-five percent confidence intervals were calculated for the MPT data at each age level. An inspection of these data (Table 2) verifies the large differences in individual MFT performance among children within a given age group in both sexes. Special interest is directed to the lower limits of the confidence intervals because of its potential clinical importance. The influence of repeated trials on MPT was studied to determine the minimum number of trials necessary to reach a subject’s longest sustained phonation. The criterion variable measured for each subject reflected the first trial that was equal to or greater than the mean of the three longest phonations. See Table 3 for the mean and SD for these data, reported for each sex and age level. Males tended to w_ork at the task of increasing the length of phonation for more trials (X = 8.6) than females (x = 7.6). Variability of the effect of repeated trials was great for both sexes. A cumulative frequency distribution was completed for these data. An examination of the frequency distribution (Table 4) revealed that only 16.2% of the males and 23% of the females achieved their longest sustained phonation by the third trial. The majority of the children did not reach MPT until the ninth trial. A x2 test was computed on the frequency distribution data. Sex and the number of trials needed to reach MPT were not significantly related (x2 (13) = 12.39, p > 0.05). MPT data were averaged over the last five trials (TIO-T14) for each age group, and these data were compared with the mean of the three longest
Table 2. Ninety-Five
Percent
Confidence
Intervals
for MPT Data
Males
Age
Lower
3 4 5
4.38 5.08
6 7 8 9 10 11 12 13 14 I5 16 17
4.15 8.06 9.11 7.98 4.94 12.91 12.43 9.02 6.29 8.84 10.32 12.43 14.83
Females
M
Wer limit/ set
Ane
Lower
M
Upper limit/ set
7.92 9.99 10.12 13.90 14.63 16.81 16.83 22.20 19.85 20.23 22.34 22.34 20.74 21.04 28.70
11.46 14.90 16.09 19.74 20.15 25.64 28.72 31.49 27.27 31.44 38.29 35.84 31.16 29.66 42.57
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
2.84 5.26 5.44 6.66 8.88 8.07 7.07 4.14 10.73 7.58 10.27 8.76 10.40 13.09 9.65
6.28 8.86 10.47 13.81 13.68 17.12 14.47 15.88 14.76 15.16 19.24 18.85 19.53 21.85 21.99
9.72 12.46 15.50 20.96 18.48 26.17 21.87 27.62 18.79 22.74 28.21 28.94 29.93 30.61 34.33
314
D. E. FINNEGAN
Table 3. Mean and SD of the Minimum
Number
Needed to Reach a
of Trials
Subject’s Longest Sustained Phonation Female n
Age 3-6 to 4-O to 5-o to 6-O to 7-o to 8-oto 9-o to 10-O to 11-o lo 12-O to 13-O to 14.0 to 15-o to 16-O to 17-O to
SD
9 10 IO 10 10 IO IO 10 10 10 10 IO
4.6 6.6 6.4 7.6 10.1 10.1 7.9 10.7 6.3 7.1 7.2 8.6 6.2 6.5 7.6
3.97 4.03 2.36 4.55 3.63 3.84 2.99 3.77 4.64 3.78 5.20 4.78 4.87 4.19 4.83
144
7.6
4.26
5
3-11 4- I1 5-11 6-11 7-11 8-11 9-11 10-I 1 II-11 12-11 13-11 14-11 15-I 1 16-l 1 17-11
10 10
Group totals
Male
M
n
M
SD
10 9 9 10 10 10 IO 9 10 10 IO 10 10
8.4 6. I 8.9 7.5 8.8 9. I 10.4 8.8 9. I 7.4 9.0 7.8 7.0 IO. I 10.6
4.27 4.62 4.53 2.40 4.51 4.55 4.14 4.13 4.48 4.77 2.86 5.15 4.78 4.17 2.91
142
8.6
4.20
5 10
sustained phonations to examine MPT after the practice effect (Table 5). Visual comparison of the data in Table 1 and Table 5 indicated a definite fatigue effect at each age level for both sexes. The group mean MFT, after the practice effect (T10-T14), was 15.84 and 13.42 set for males and females, respectively. Males sustained phonation significantly longer than females after the practice effect (t (28) = 2.627; p < 0.05). Table 4. Cumulative Frequency Distribution Indicating Number of Trials Needed to Reach the Mean of the Three Longest Sustained Phonations Male trials
f
%
14
18
12.7
142
13 12 11 10 9 8 I 6 5 4 3 2 1
13 12 II 14 11 9 8 11 7 5 5 8 10
9.1 8.4 7.7 9.8 7.7 6.3 5.6 7.7 4.9 3.5 3.5 5.6 7.0
124 111 99 88 74 63 54 46 35 28 23 18 10
CF
Female trials
.f
100.0
14
87.3 78.2 69.7 62.0 52.1 43.4 38.0 32.4 24.6 19.7 16.2 12.6 7.0
13 12 I1 10 9 8 I 6 5 4 3 2 1
Cumulative %
%
CF
12
8.3
144
16 7 8 14 7 13 9 7 6 12 8 14 II
11.1 4.9 5.5 9.7 4.9 9.0 6.2 4.9 4.2 8.3 5.5 9.7 7.6
132 116 109 101 87 80 67 58 51 45 33 25 II
Cumulative % 100.0 91.7 80.5 75.7 70.1 60.4 55.5 46.5 40.3 35.4 31.2 23.0 17.4 8.0
MAXIMUM
PHONATION
TIME
315
Table 5. MFT Averaged for the Last Five Trials (TIO-T14). MPT After the Practice Effect Males Age/Yr 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Females
Mlsec
SD
Age/Y r
Mlsec
SD
6.37 7.83 8.89 12.07 12.92 15.57 15.32 20.28 18.01 17.56 19.94 18.99 18.86 18.92 26.15
1.80 2.13 3.18 3.25 2.64 4.59 5.49 4.49 3.35 4.91 7.47 6.24 4.90 4.23 6.85
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
5.18 6.62 9.08 11.77 12.55 14.49 13.16 14.60 12.77 13.77 16.47 16.94 16.72 19.47 18.71
1.66 1.62 2.57 3.28 2.60 3.00 3.60 6.16 1.86 3.61 4.06 4.61 4.50 4.68 5.23
DISCUSSION A revised methodology for measuring MPT was devised and data collected from 286 male and female children between the ages of 3-6 and 17-11 years. The influence of sex, age, and repeated trials on MPT was investigated. Male phonated significantly longer than females, both before (pre-10th trial) and after the practice effect (post-10th trial). On the average, males sustained phonation 2 set longer than females. These findings are consistent with those reported in the literature and need no further explanation (Launer, 1971; Harris, 1971; Platt et al., 1975; Lewis, 1977; Tait and Michel, 1977). In addition, males tended to be more motivated to increase the length of phonation over repeated trials than females. MPT increased as a function of age. A definite monotonic trend in the data across all age levels was not observed for either sex. Similar findings were reported by Launer (1971), Coombs (1976), Lewis (1977), and Tait and Michel (1977). The extent of the difference in MPT for the youngest and oldest subjects in the study, approximately 21 and 16 set for males and females, respectively, was larger than the differences previously reported in the literature. Launer (1971) noted a range of only 5-6 set between phonation times for 9- and 17-yr-olds. Tait and Michel (1977) observed a difference of 9 and 6 set in the length of sustained phonation for 5- and 9-yr-old males and females. The revised methodology used in this study is offered as an explanation for these differences. Optimum performance for MPT can be enhanced by following these data collection
316
D. E. FINNEGAN
techniques: (a) visual feedback and encouragement regarding depth of inhalation provided prior to each trial; (b) verbal instructions and encouragement regarding increased phonation time provided prior to and during each trial; (c) visual feedback of performance continuously provided by self-monitoring on a digital readout device; and (d) repeated trials. The average 95% critical region of MPT for males and females was between 9-27 and 8-23 set, respectively. The lower limit of the critical region is clinically more important. Traditionally, it has served as a benchmark figure for determining normalcy of MPT. Continuing this standard clinical interpretation, using group data from the present study, a female child’s MPT is considered abnormal if it is less than 8 set, and a male child’s MPT is considered abnormal if it is less that 9 sec. Repeated trials are necessary to obtain optimum performance during motor tasks similar to the MPT task, because children frequently do not exert early maximum efforts. Lewis (1977) found that only 2% of children produced their longest phonation by the third trial. In the present study, only 20% of the children reached MPT by trial three. The majority of the subjects did not reach MPT until the ninth trial. The use of repeated trials is not clinically unfeasible. The average amount of time needed to repeat nine trials involves 6-7 min (average MPT = 17 set, plus a 30-set rest period inserted between each trial). A serious limitation in interpretation of MPT, inter- and intrasubject variability, is present in this and previously reported studies of MPT for children. Possible factors contributing to the intersubject variability within similar age groups include differences in body height and weight, competiveness, motivation, and degree of maximum effort exerted. Factors contributing to intrasubject variability include differences in practice effect and consistency of exerting maximum effort. The large intra- and intersubject variability prevent valid individual to group mean comparison of MPT. The traditional technique of interpreting MPT needs further revision. A more discriminating clinical interpretation, one that would be more sensitive to individual differences in MPT, is warranted. Bless and Hirano (1982a,b) have designed such a methodology for adults. The next step is to use this methodology with children. REFERENCES Bless, D. and Hirano, M. (1982a). Verbal instructions: A critical variable in obtaining optimal performance for maximum phonation time. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Toronto, Canada.) Bless, D. and Hirano, M. (1982b). Estimation of glottal air flow and maximum phonation time as a clinical tool. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Toronto, Canada.)
MAXIMUM
PHONATION
TIME
317
Coombs, J. (1976). The maximum duration of phonation of /a/ in normal and hoarse-voiced children. (Unpublished Master’s thesis, Portland State University.) Harris, T. (1971). Aerodynamic and perceptual characteristics of normal and dysphonic children. (Unpublished Master’s thesis, Purdue University.) Launer, P. (1971). Maximum phonation time in children. thesis, University of New York at Buffalo.)
(Unpublished
Master’s
Lewis, J. (1977). The maximum duration of phonation of /a/ in normal-voiced 8and lo-year-old children. (Unpublished Master’s thesis, Portland State University.) Looney, N. and Harden, J. (1980). Duration of sustained phonation in kindergarten children. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Detroit.) McQueen, D. and Saxman, J. (1970). Maximum phonation time, air flow rate, and air volume during phonation: Normative information on third grade children. (Paper presented at the Annual Convention of the American SpeechLanguage-Hearing Association, New York.) Platt, L., Harris, T., Burk, K., Perez, D., and Grizzel, B. (1975). Maximum phonation time and air flow rate of children with and without vocal nodules. .I. Kansas Speech Hear. Assoc. 15~45-55. Tait, N. and Michel, J. (1977). Maximum duration of sustained /s/ and /z/ in children. (Paper presented at the Annual Convention of the American SpeechLanguage-Hearing Association, San Francisco.)
MAXIMUM PHONATION TIME FOR CHILDREN WITH NORMAL VOICES DENIS E. FINNEGAN Speech Pathology and Audiology Department James Madison University, Harrisonburg, Virginia
Maximum phonation time (MPT) data were collected for 286 male and female children between the ages 3-6 and 17-11. Subjects sustained phonation of the vowel /a/ for 14 consecutive trials. The influence of sex, age, and multiple trials on MPT was studied. The group mean MPT for the male subjects was significantly longer than for the female subjects. Generally, phonation time increased with age for both sexes. A definite monotonic increase in length of sustained phonation was not apparent across all age levels. Optimum MPT performance can be enhanced by using repeated trials, and by providing visual feedback and encouragement regarding depth of inhalation, verbal instructions and encouragement regarding increased phonation time, and visual feedback regarding length of sustained phonation prior to and during each trial. The large intra- and intersubject variability in MPT performance reported in this study prevents valid individual-group mean MPT comparisons. A more discriminatory clinical interpretation of MPT is necessary.
INTRODUCTION The present study was conducted to investigate the influence of sex, age, and multiple trials on maximum phonation time (MPT) for a large group of children with normal voices. For the purpose of this study, MPT was defined as the length of time that an individual could sustain an isolated vowel without the appearance of glottal fry or a substantial decrease in loudness (Launer, 1971). The measure of MPT reflected the mean of the three longest trials. Investigations of MPT for young children and adolescents have been numerous (McQueen and Saxman, 1970; Launer, 1971; Harris, 1971; Platt et al., 1975; Coombs, 1976; Lewis, 1977; Tait and Michel, 1977; Looney and Harden, 1980). Researchers agree that a wide range of variability exists in MPT both between and within children across trials. Children with normal voices produce longer phonation times than children with vocal pathologies, and children sustain certain vowels, such as /i/ for l2 set longer than others, such as /a/. Address correspondence to: Denis E. Finnegan, Ph.D., Speech Pathology and Audiology Department, New Education Building, James Madison University, Harrisonburg, VA 22807. 0 1984 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017
309 002 I-9924/84/$03.00
310
D. E. FINNEGAN
Conflicting results exist involving the influence of sex and age on MPT. Launer (1971), Harris (1971), Platt et al. (1975), and Lewis (1977) reported that males sustained phonation longer than females, while McQueen and Saxman (1970), Tait and Michel (1977), and Looney and Harden (1980) found that the main effect of sex was not significant. Launer (1971), Coombs (1976). and Tait and Michel (1977) indicated that phonation time tended to increase with age; however, a definite linear trend was not found. Conversely, Lewis (1977) demonstrated that age was not a significant factor in relation to phonation time. Lewis (1977) was the only investigator to study the influence of repeated trials on MPT for children. Subjects sustained production of la/ for 20 consecutive trials. Lewis found that only 2% of the children produced their longest phonation by the third trial. Lewis’ study was incomplete, however, because the influence of repeated trials was measured for only two different age groups. Normative MPT for children is important to serve as a valid indicator of phonatory function, Present normative data is both invalid and incomplete. Children were not allowed a sufficient number of trials to achieve their “maximum phonation,” and most investigators sampled an age range of fewer than 5 yr. The largest age range sampled in a single study was 9 yr (Launer, 1971). The methodology for measuring MPT must be revised, and the age range sampled must be expanded to provide valid and complete normative standards. These data can then be used as a meaningful measure for screening voice disorders in children. A refined methodology was devised and MPT was sampled across a 14.5yr range. The influence of sex, age, and repeated trials on length of phonation was investigated.
METHODS Subjects Subjects for the study came from northwestern Virginia. Fifteen schools were randomly selected from a total of 56 possible preschool, primary, and secondary schools within a three-county area. Five of the schools were preschool, seven were primary, and three were secondary. With the exception of the preschools, each school had between two and four different classes at each grade level. An equal number of children were selected randomly from each class, at each grade level, from each primary and secondary school. Data were collected for 286 children ranging in age from 3-6 to 17-l I. Ten male and ten female children were grouped at each 12-mo interval. All children were considered by their classroom teacher to be of normal intelligence and to be emotionally stable. Caucasian, Afro-American, and
MAXIMUM
PHONATION
TIME
311
Oriental children residing in urban and rural environments were included in the sample. Subjects represented low, middle, and upper income families. No child who was physically handicapped or currently enrolled in speech therapy was selected for inclusion in the study. All children were judged by the experimenter (a speech pathologist with 9 yr of experience) to have age-appropriate articulation, normal structure and function of the oral peripheral mechanism, a habitual pitch and modal loudness level appropriate for their age, sex, and body size, and fluent speech. In addition, all subjects passed a pure tone hearing screening. Procedure MPT data were recorded on an individual basis. All testing was conducted in a quiet, familiar room within each child’s school. The experimental task consisted of sustaining phonation of the vowel /a/ for 14 trials. Each phonation was tape recorded. Pitch was controlled through the repeated use of a carrier phrase preceding the production of the isolated vowel /a/. Children were instructed to say the carrier phrase, “I call my mother Ma,” in their normal voice. Then, they were instructed to repeat the phrase, prolonging the vowel in the final word for several seconds. Loudness was controlled by self-monitoring the needle indicator deflection on the VU meter of the tape recorder. Each child was instructed to maintain a zero reading as he/she prolonged the /a/ vowel. Immediately prior to each trial, subjects were instructed to visually monitor their inhalation by inhaling through the plastic connection tube in the Triflo II - Incentive Deep-Breathing Exerciser (Chesebrough Ponds, Inc., model 5-7173). Visual feedback provided by the Triflo II motivated the children to inhale maximally before each phonation. Immediately following inhalation, subjects were instructed to sustain the vowel /a/ for as long as possible, using the previous carrier phrase as a reference point for maintaining a habitual pitch level. Subjects received visual feedback regarding the duration of phonation continuously by self-monitoring on a digital readout device (Coulbourn Electronic Counter, model R 11-25). They were encouraged to increase the duration on the succeeding trial. A 30-set rest period was inserted between each trial. No child was recorded following participation in a vigorous physical activity, such as gym, band, or recess. A stop watch was used to measure phonation time live voice. Following data collection, the tape recorded production of each child’s phonation was played into a graphic-level recorder (General Radio model 1521-B) to produce a permanent record and to provide a graphic indication of the rise and fall of intensity, hence, the onset and cessation of phonation time. Measurements of MPT produced by each subject were also obtained from this record.
312
D. E. FINNEGAN
RESULTS Intrajudge reliability of measuring MPT using the stop watch was completed 12 wk following data collection for a random sample of 25 children. The correlation between the two stopwatch measurements was statistically significant (r = +0.96; t(23) = 3.06; p < 0.01). All live stop watch measurements were compared with their countermeasurements derived from the graphic-level recorder. The two measurements were highly related (r = +0.89; ~(285) = 15.06; p < 0.01). The mean and standard deviation of the three longest sustained phonations, measured in seconds and categorized according to sex and age level, are presented in Table 1. The group mean of the three longest sustained phonations for the male children was 18.23 set; the total sample standard deviation was 7.20 set, and 15.79 and 5.72 set, respectively, for the female children. The group mean MPT for the males was significantly longer than for the females [t(284) = 3.26; p < 0.011. Males phonated longer than females in 12 of 15 age groups. The only age levels where females sustained phonation longer than males were: 5-O to 5-1 I, 8-O to 8-11, and 16-O to 16-11. The mean of the three longest phonations for males increased from 7.92 set for the 3.5-yr-olds to 28.70 set for the 17.5-yr-olds, and those for the females increased from 6.28 set for the 3.5-yr-olds to 21.99 set for the 17.5-yr-olds. A definite monotonic increase in length of sustained phonation was not apparent across all age levels for either sex. Table 1. Mean and SD of the Three Longest in Seconds (n = 286)
Sustained
Phonations
Female subjects Age 3-6 to 4-oto 5-o to 6-Oto 7-o to 8-O to 9-o to 10-O to II-0 to 12-o to 13-o to 14.0 to 15-O to 16-O to 17-O to
3-11 4-11 5-11 6-11 7-11 8-11 9-11 IO-1 I 11-11 12-11 13-t I 14-11 15-11 16-I 1 17-11
Grouo totals
n
Measured
Male subjects M
SD
5 10 10 9 9 IO 10 10 IO 9 10 10 10 10 10
7.92 9.99 10.12 13.90 14.63 16.81 16.83 22.20 19.85 20.23 22.34 22.34 20.74 21.04 28.70
1.81 2.51 3.05 2.98 2.82 4.51 6.07 4.74 3.79 5.72 8.19 6.89 5.32 4.40 7.08
142
18.23
7.20
M
SD
n
5 10 IO 9 10 10 10 10 10 10 10 10 10 10 10
6.28 8.86 10.47 13.81 13.68 17.12 14.47 15.88 14.76 15.16 19.24 18.85 19.53 21.85 21.99
1.76 1.84 2.57 3.65 2.45 4.62 3.78 5.99 2.06 3.87 4.58 5.15 4.66 4.47 6.30
144
15.79
5.72
MAXIMUM
PHONATION
TIME
313
Ninety-five percent confidence intervals were calculated for the MPT data at each age level. An inspection of these data (Table 2) verifies the large differences in individual MFT performance among children within a given age group in both sexes. Special interest is directed to the lower limits of the confidence intervals because of its potential clinical importance. The influence of repeated trials on MPT was studied to determine the minimum number of trials necessary to reach a subject’s longest sustained phonation. The criterion variable measured for each subject reflected the first trial that was equal to or greater than the mean of the three longest phonations. See Table 3 for the mean and SD for these data, reported for each sex and age level. Males tended to w_ork at the task of increasing the length of phonation for more trials (X = 8.6) than females (x = 7.6). Variability of the effect of repeated trials was great for both sexes. A cumulative frequency distribution was completed for these data. An examination of the frequency distribution (Table 4) revealed that only 16.2% of the males and 23% of the females achieved their longest sustained phonation by the third trial. The majority of the children did not reach MPT until the ninth trial. A x2 test was computed on the frequency distribution data. Sex and the number of trials needed to reach MPT were not significantly related (x2 (13) = 12.39, p > 0.05). MPT data were averaged over the last five trials (TIO-T14) for each age group, and these data were compared with the mean of the three longest
Table 2. Ninety-Five
Percent
Confidence
Intervals
for MPT Data
Males
Age
Lower
3 4 5
4.38 5.08
6 7 8 9 10 11 12 13 14 I5 16 17
4.15 8.06 9.11 7.98 4.94 12.91 12.43 9.02 6.29 8.84 10.32 12.43 14.83
Females
M
Wer limit/ set
Ane
Lower
M
Upper limit/ set
7.92 9.99 10.12 13.90 14.63 16.81 16.83 22.20 19.85 20.23 22.34 22.34 20.74 21.04 28.70
11.46 14.90 16.09 19.74 20.15 25.64 28.72 31.49 27.27 31.44 38.29 35.84 31.16 29.66 42.57
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
2.84 5.26 5.44 6.66 8.88 8.07 7.07 4.14 10.73 7.58 10.27 8.76 10.40 13.09 9.65
6.28 8.86 10.47 13.81 13.68 17.12 14.47 15.88 14.76 15.16 19.24 18.85 19.53 21.85 21.99
9.72 12.46 15.50 20.96 18.48 26.17 21.87 27.62 18.79 22.74 28.21 28.94 29.93 30.61 34.33
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D. E. FINNEGAN
Table 3. Mean and SD of the Minimum
Number
Needed to Reach a
of Trials
Subject’s Longest Sustained Phonation Female n
Age 3-6 to 4-O to 5-o to 6-O to 7-o to 8-oto 9-o to 10-O to 11-o lo 12-O to 13-O to 14.0 to 15-o to 16-O to 17-O to
SD
9 10 IO 10 10 IO IO 10 10 10 10 IO
4.6 6.6 6.4 7.6 10.1 10.1 7.9 10.7 6.3 7.1 7.2 8.6 6.2 6.5 7.6
3.97 4.03 2.36 4.55 3.63 3.84 2.99 3.77 4.64 3.78 5.20 4.78 4.87 4.19 4.83
144
7.6
4.26
5
3-11 4- I1 5-11 6-11 7-11 8-11 9-11 10-I 1 II-11 12-11 13-11 14-11 15-I 1 16-l 1 17-11
10 10
Group totals
Male
M
n
M
SD
10 9 9 10 10 10 IO 9 10 10 IO 10 10
8.4 6. I 8.9 7.5 8.8 9. I 10.4 8.8 9. I 7.4 9.0 7.8 7.0 IO. I 10.6
4.27 4.62 4.53 2.40 4.51 4.55 4.14 4.13 4.48 4.77 2.86 5.15 4.78 4.17 2.91
142
8.6
4.20
5 10
sustained phonations to examine MPT after the practice effect (Table 5). Visual comparison of the data in Table 1 and Table 5 indicated a definite fatigue effect at each age level for both sexes. The group mean MFT, after the practice effect (T10-T14), was 15.84 and 13.42 set for males and females, respectively. Males sustained phonation significantly longer than females after the practice effect (t (28) = 2.627; p < 0.05). Table 4. Cumulative Frequency Distribution Indicating Number of Trials Needed to Reach the Mean of the Three Longest Sustained Phonations Male trials
f
%
14
18
12.7
142
13 12 11 10 9 8 I 6 5 4 3 2 1
13 12 II 14 11 9 8 11 7 5 5 8 10
9.1 8.4 7.7 9.8 7.7 6.3 5.6 7.7 4.9 3.5 3.5 5.6 7.0
124 111 99 88 74 63 54 46 35 28 23 18 10
CF
Female trials
.f
100.0
14
87.3 78.2 69.7 62.0 52.1 43.4 38.0 32.4 24.6 19.7 16.2 12.6 7.0
13 12 I1 10 9 8 I 6 5 4 3 2 1
Cumulative %
%
CF
12
8.3
144
16 7 8 14 7 13 9 7 6 12 8 14 II
11.1 4.9 5.5 9.7 4.9 9.0 6.2 4.9 4.2 8.3 5.5 9.7 7.6
132 116 109 101 87 80 67 58 51 45 33 25 II
Cumulative % 100.0 91.7 80.5 75.7 70.1 60.4 55.5 46.5 40.3 35.4 31.2 23.0 17.4 8.0
MAXIMUM
PHONATION
TIME
315
Table 5. MFT Averaged for the Last Five Trials (TIO-T14). MPT After the Practice Effect Males Age/Yr 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Females
Mlsec
SD
Age/Y r
Mlsec
SD
6.37 7.83 8.89 12.07 12.92 15.57 15.32 20.28 18.01 17.56 19.94 18.99 18.86 18.92 26.15
1.80 2.13 3.18 3.25 2.64 4.59 5.49 4.49 3.35 4.91 7.47 6.24 4.90 4.23 6.85
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
5.18 6.62 9.08 11.77 12.55 14.49 13.16 14.60 12.77 13.77 16.47 16.94 16.72 19.47 18.71
1.66 1.62 2.57 3.28 2.60 3.00 3.60 6.16 1.86 3.61 4.06 4.61 4.50 4.68 5.23
DISCUSSION A revised methodology for measuring MPT was devised and data collected from 286 male and female children between the ages of 3-6 and 17-11 years. The influence of sex, age, and repeated trials on MPT was investigated. Male phonated significantly longer than females, both before (pre-10th trial) and after the practice effect (post-10th trial). On the average, males sustained phonation 2 set longer than females. These findings are consistent with those reported in the literature and need no further explanation (Launer, 1971; Harris, 1971; Platt et al., 1975; Lewis, 1977; Tait and Michel, 1977). In addition, males tended to be more motivated to increase the length of phonation over repeated trials than females. MPT increased as a function of age. A definite monotonic trend in the data across all age levels was not observed for either sex. Similar findings were reported by Launer (1971), Coombs (1976), Lewis (1977), and Tait and Michel (1977). The extent of the difference in MPT for the youngest and oldest subjects in the study, approximately 21 and 16 set for males and females, respectively, was larger than the differences previously reported in the literature. Launer (1971) noted a range of only 5-6 set between phonation times for 9- and 17-yr-olds. Tait and Michel (1977) observed a difference of 9 and 6 set in the length of sustained phonation for 5- and 9-yr-old males and females. The revised methodology used in this study is offered as an explanation for these differences. Optimum performance for MPT can be enhanced by following these data collection
316
D. E. FINNEGAN
techniques: (a) visual feedback and encouragement regarding depth of inhalation provided prior to each trial; (b) verbal instructions and encouragement regarding increased phonation time provided prior to and during each trial; (c) visual feedback of performance continuously provided by self-monitoring on a digital readout device; and (d) repeated trials. The average 95% critical region of MPT for males and females was between 9-27 and 8-23 set, respectively. The lower limit of the critical region is clinically more important. Traditionally, it has served as a benchmark figure for determining normalcy of MPT. Continuing this standard clinical interpretation, using group data from the present study, a female child’s MPT is considered abnormal if it is less than 8 set, and a male child’s MPT is considered abnormal if it is less that 9 sec. Repeated trials are necessary to obtain optimum performance during motor tasks similar to the MPT task, because children frequently do not exert early maximum efforts. Lewis (1977) found that only 2% of children produced their longest phonation by the third trial. In the present study, only 20% of the children reached MPT by trial three. The majority of the subjects did not reach MPT until the ninth trial. The use of repeated trials is not clinically unfeasible. The average amount of time needed to repeat nine trials involves 6-7 min (average MPT = 17 set, plus a 30-set rest period inserted between each trial). A serious limitation in interpretation of MPT, inter- and intrasubject variability, is present in this and previously reported studies of MPT for children. Possible factors contributing to the intersubject variability within similar age groups include differences in body height and weight, competiveness, motivation, and degree of maximum effort exerted. Factors contributing to intrasubject variability include differences in practice effect and consistency of exerting maximum effort. The large intra- and intersubject variability prevent valid individual to group mean comparison of MPT. The traditional technique of interpreting MPT needs further revision. A more discriminating clinical interpretation, one that would be more sensitive to individual differences in MPT, is warranted. Bless and Hirano (1982a,b) have designed such a methodology for adults. The next step is to use this methodology with children. REFERENCES Bless, D. and Hirano, M. (1982a). Verbal instructions: A critical variable in obtaining optimal performance for maximum phonation time. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Toronto, Canada.) Bless, D. and Hirano, M. (1982b). Estimation of glottal air flow and maximum phonation time as a clinical tool. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Toronto, Canada.)
MAXIMUM
PHONATION
TIME
317
Coombs, J. (1976). The maximum duration of phonation of /a/ in normal and hoarse-voiced children. (Unpublished Master’s thesis, Portland State University.) Harris, T. (1971). Aerodynamic and perceptual characteristics of normal and dysphonic children. (Unpublished Master’s thesis, Purdue University.) Launer, P. (1971). Maximum phonation time in children. thesis, University of New York at Buffalo.)
(Unpublished
Master’s
Lewis, J. (1977). The maximum duration of phonation of /a/ in normal-voiced 8and lo-year-old children. (Unpublished Master’s thesis, Portland State University.) Looney, N. and Harden, J. (1980). Duration of sustained phonation in kindergarten children. (Paper presented at the Annual Convention of the American Speech-Language-Hearing Association, Detroit.) McQueen, D. and Saxman, J. (1970). Maximum phonation time, air flow rate, and air volume during phonation: Normative information on third grade children. (Paper presented at the Annual Convention of the American SpeechLanguage-Hearing Association, New York.) Platt, L., Harris, T., Burk, K., Perez, D., and Grizzel, B. (1975). Maximum phonation time and air flow rate of children with and without vocal nodules. .I. Kansas Speech Hear. Assoc. 15~45-55. Tait, N. and Michel, J. (1977). Maximum duration of sustained /s/ and /z/ in children. (Paper presented at the Annual Convention of the American SpeechLanguage-Hearing Association, San Francisco.)