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Comfortable effort level revisited
Journal of Voice
V~I. 10, No. 3, pp. 299-305 © 1996 Lippincott-Raven Publishers, Philadelphia
Comfortable Effort Level Revisited W. S. Brown, Jr., *Richard J. Morris, and tThomas Murry Institute for Advanced Study of the Communication Processes, University of Florida, Gainesville, Florida; *Department of Communication Disorders, Florida State University, Tallahassee, Florida; and "~Department of Otolaryngology, University of Tennessee, College of Medicine, Memphis, Tennessee, U.S.A.
Summary: The purpose of this study was to measure the variability of frequency and intensity of speech, using multiple voice samples obtained over a period of time at a speaker's "comfortable effort level." Variability in vocal output within and across several experimental sessions was assessed from measures of speaking fundamental frequency (SFF) and vocal intensity for utterances repeated three times a day over a 3-day period. Three distinct age groups of men and women--young, middle-aged and elderly--repeated the vowel/o/, read a standard passage, and spoke extemporaneously during each experimental session. Results indicated that variability in SFF and intensity were present across experimental sessions, age groups, gender, and speaking samples. Generally, group means indicated that ---+1 semitone of variability for SFF and - 2 db sound pressure level (SPL) variation in vocal intensity from any one experimental session to the next could be expected; individual variations within any group may reach two semitones and 6 db SPL. Key Words: Comfortable effort--Comfortable effort level--Effort level--Vocal effort.
In an effort to examine laryngeal behavior under normal speaking conditions, experimenters often ask subjects to repeat vocal utterances at a " c o m fortable effort level." When experimenters refer to " c o m f o r t a b l e " , they are usually specifying, operationally, the level of effort that is expended by a speaker as reflected by such vocal parameters as fundamental f r e q u e n c y and/or intensity. The term " c o m f o r t a b l e effort l e v e l " and analogous terms such as " h a b i t u a l " and " n a t u r a l " , imply that there is a level of vocal or speech output, or " e f f o r t " , which, for a speaker, is typical when repeating an utterance. It may be hypothesized that instructions to produce a sample o f speech in a comfortable
manner do not place regulations on a subject's vocal output as do external controls, for which the speaker's output is monitored according to the experimenter's specifications. When external controls are placed on the s p e a k e r ' s output, the experimenter uses specific instrumentation to be assured that the subject is producing the particularly desired response. When speakers set their own level of vocal output at their " c o m f o r t a b l e " or " n a t u r a l " mode, there is no assurance that the subjects will use the same frequency/intensity parameters o v e r repeated sampling periods. The present authors, nearly 20 years ago, presented data directly related to the vocal variability associated with experimental instructions to produce s p e e c h samples at a " c o m f o r t a b l e e f f o r t level" (1). Since that time, several other reports of vocal variability have appeared in the research literature (2-4). Results of the reported studies indicated, generally, that vocal output did vary from one experimental session to the next when subjects were instructed to produce the vocal samples in a
Accepted March 23, 1995. Address correspondence and reprint requests to Dr. W. S. Brown, Jr. at Institute for Advanced Study of the Communication Processes, 63 Dauer Hall, University of Florida, Gainesville, FL 32611, U.S.A. Results of this study were presented at the 22nd Annual Symposium, Care of the Professional Voice, Philadelphia, PA, U.S.A. June 9, 1993.
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W. S. B R O W N ET AL.
comfortable manner. More importantly, given that variability of vocal output at comfortable effort does exist, it remains to be determined if this variability represents a significant compromise to voice sampling or whether sampling one's comfortable effort should be eliminated from single sampling studies. Results of the present investigators' study reported in 1976 (1) revealed that across 5 successive days, for the production of sustained vowels and short phrases, the majority of speakers were relatively stable in their utterances across sessions. However, individual speakers were found to vary as much as 4 semitones, or - 2 0 Hz, across the 5-day period. More recently, in 1987, Garrett and Healey (2) reported that a group of men exhibited significant within-speaker changes in speaking fundamental frequency (SFF) from morning to noon to late afternoon, whereas their female counterparts revealed no significant changes across recording sessions. Contrarily, in 1990, Nittrouer et al. (3) reported that SFF was not affected by the time of day in which the measures are taken. They reported no significant differences in SFF for either men or women when vocal utterances were compared for the early morning versus late afternoon. In 1991, Coleman and Markham (4) concluded that, in adult talkers, habitual pitch appears to be a stable measurement that varies a relatively small amount over a month, a year, or, even a decade. They viewed their finding of a 2.74 semitone average variation in SFF for a group of normal young women over a 30-day period to be clinically acceptable. Coleman and Markham also pointed out that this average variation may or may not be acceptable for other, nonclinical purposes. PURPOSE The use of comfortable effort level has relevance to voice scientists, speech pathologists, physicians, and voice teachers alike, as each has specific interests in knowing the variability that exists in a speaker's vocal utterances. This study was designed to revisit the issue of vocal variability. The purpose was to obtain measures of SFF and vocal intensity at the comfortable effort level in order to assess the degree of variability in vocal output across utterance types and recording sessions. Unlike previous studies, which have focused either on the speech material or the variation across sessions, the present study includes measures of SFF and vocal Journal of Voice, Vol. I0, No. 3, 1996
intensity for utterances repeated over a 3-day period and at three different time periods of each day. Moreover, this study expands the speaker population to include men and women representing three distinct age groups-young, middle-aged, and old. METHODS The subjects of this study were 50 untrained speakers divided into three age groups: nine men (range, 21-33 years of age) and 10 women (range, 20-22 years) in the 20-35 year age range (young); nine men (range, 40-54 years of age) and nine women (range, 42-50 years of age) in the 40-55 year age range (middle-aged); and six men (range, 69-87 years of age) and seven women (range, 65-89 years of age) who were/>65 years (old). All subjects were in good health and it was agreed by both subjects and experimenters that subjects had normal speech and hearing for their age group. None of the subjects reported any neurological or respiratory problems or diseases, nor did they report any common illnesses (i.e., colds or flu) during the week of recording which may have had a temporary effect on vocal output. Each subject was seated in a noise-free environment at a constant mouth-to-microphone distance of I0 in. For each experimental session, subjects were asked to phonate the v o w e l / a / f o r 10 s, read the first paragraph of the Rainbow Passage (5), and speak extemporaneously for 30 s, prompted by a picture that was different for each experimental session. The only prior instruction given to subjects for each of the three speaking samples was to produce the sample at a comfortable effort level. Each subject's utterances were recorded on audio tape (Shure Microphone, 545SD coupled to a Teac X300R tape recorder). Speech samples were produced three times during a l-week time frame three times daily: once in the morning between 8:00 and 10:00 a.m., once in the early afternoon between 12:00 and 2:00 p.m., and once in the late afternoon between 4:00 and 6:00 p.m. Prior to each recording session, a calibration tone of I000 Hz at 74 db, via a Wavetek 133 function generator and presented through a loudspeaker placed 10 in from the microphone, was recorded on the tape. This calibration tone served as the reference from which to calculate vocal intensity in relative db. The calibration tone was also used to verify playback tape speed for each recording session. To determine average SFF, tape recorded utter-
COMFORTABLE EFFORT LEVEL REVISITED ances were analyzed by means of FFI-8, the current version of the IASCP Fundamental Frequency Indicator (6). Processing by this method yielded the mean SFF in Hz and semitones (reference = 16.35159). Relative vocal intensity was determined by playing the tape recorded utterances of the vowel, the second sentence of the Rainbow Passage and - 3 s of the extemporaneous speech sample through a Bruel and Kjaer graphic level recorder at a writing speed (slew rate) of 250 mm/s and paper speed of 30 mm/s. Each reading and speaking sample produced 14-16 energy peaks, which were measured in relative db and averaged. The average value represented mean (relative) vocal intensity for each sample utterance. And, finally, a repeated measures analysis of variance (ANOVA) (by sex by day by time) was applied to the data to determine statistical significance at the 0.05 confidence level. Separate ANOVAs were determined for each task--sustained vowel, oral reading, and spontaneous speaking, as well as for SFF and intensity--resulting in a total of six ANOVAs. RESULTS Tables 1 and 2 have been simplified by collapsing the data over days and times of day, presenting group means and standard deviations for each age group and speaking condition. The data in these two tables are exemplary of some of the more obvious trends associated with the variability exhibited by these groups of speakers. Even though Table 1 presents the SFF data in both Hz and semitones, the semitone data will prevail as the primary indicator of group variability. This treatment of the data is more traditional as fundamental frequency is logarithmic and, thus, the use of the semitone measure
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allows for a more valid comparison of male and female voices, which tend to be an octave apart on the musical scale. Tables 3 and 4 present the reader with the mean SFF and average vocal intensity data for men and women, associated with the three speaking conditions for each of the 3 days and for each of the times of day across the three age groups. The data in these two tables give the reader a broader view of the overall distribution of within- and betweengroup variabilities and also can be referred to in relation to the statistical treatment of the data. SFF Overall, statistical analysis revealed that for all tasks, women, as would be expected, spoke at significantly higher levels than did men. As can be seen in Table 1, in most cases the highest variability in SFF occurred for the vowel productions, with standard deviations ranging from 1.0 to 1.7 semitones. In comparison, reading and speaking productions generally exhibited smaller standard deviations, ranging from 0.6 to 1.3 semitones. Moreover, the 65-89 year old group, especially the women, demonstrated somewhat more variability in vowel productions in comparison to that associated with their younger counterparts. This was not the case for reading and speaking conditions, however, in which the semitone standard deviations were essentially comparable within gender groups. Across age groups and across all speaking conditions, men appeared to be somewhat more variable than women. Several interactions for all three speaking conditions are worth noting. For sustained productions, analysis revealed a significant age by sex by day interaction [F(6,82) = 2.74, p < 0.05]. The data indicated that older women spoke at significantly
T A B L E 1. Group means (M) and standard deviations (SD) collapsed across days and times of day associated with
SFF reported in Hz (and semitones) for each of the three age groups and speaking samples Vowel Subjects
Reading
Speaking
M
SD
M
SD
M
SD
Women Young Middle-aged Old
209 (44) 198 (43) 189 (42)
12 (I.0) 14 (!.2) 18 (I.7)
195 (43) 194 (43) 170 (41)
10 (0.9) 10 (0.9) 9 (0.6)
189 (42) 186 (42) 175 (41)
9 (0.8) 9 (0.9) 9 (0.8)
Men Young Middle-aged Old
123 (35) 124 (35) 142 (37)
I1 (I.4) 9 (I.3) 15 (I.5)
137 (37) 135 (36) 139 (37)
6 (1.3) 7 (1.0) 7 (0.9)
136 (37) 128 (36) 134 (36)
9 (1.1) 7 (0.9) 8 (1.1)
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W. S. B R O W N E T A L .
TABLE 2. Group means (M) and standard deviations (SD) collapsed across days and times of day associated with
vocal intensity (in relative db) for each of the three age groups and speaking samples Vowel Su~ects Women Young Middle-aged Old Men Young Middle-aged Old
Reading
Speaking
M
SD
M
SD
M
SD
63 66 66
2.7 2.3 3.8
65 67 70
1.9 1.7 2.2
63 66 68
2.3 2.3 2.4
66 68 75
3.5 2.8 3.2
68 68 75
1.9 2. I 2.3
67 67 74
2.5 2.4 2.6
l o w e r S F F levels t h a n did the y o u n g a n d m i d d l e aged w o m e n o n d a y 3 (Table 3), while o l d e r m e n s p o k e at s i g n i f i c a n t l y h i g h e r S F F levels t h a n did y o u n g a n d m i d d l e aged m e n o n all 3 d a y s (Table 4). A m o n g the w o m e n , a significant age by d a y intera c t i o n [F(4,40) = 5.04, p < 0.05] o c c u r r e d . M i d d l e aged w o m e n s p o k e at h i g h e r S F F levels o n d a y 3, while y o u n g e r a n d o l d e r w o m e n e x h i b i t e d no sign i f i c a n t d i f f e r e n c e a c r o s s d a y s (Table 3). F o r the m e n , n o significant d i f f e r e n c e s o c c u r r e d for S F F a c r o s s d a y s w i t h i n the age g r o u p s . F o r r e a d i n g , a significant age b y sex S F F inter-
a c t i o n o c c u r r e d [F(2,43) = 3.85, p < 0.05]. O l d e r w o m e n read at s i g n i f i c a n t l y l o w e r f r e q u e n c i e s t h a n did y o u n g e r a n d m i d d l e - a g e d w o m e n for all s e s s i o n s ( T a b l e 3), while m e n did n o t differ s i g n i f i c a n t l y a m o n g age g r o u p s ( T a b l e 4). M o r e o v e r , a s i g n i f i c a n t age b y d a y i n t e r a c t i o n was f o u n d a m o n g the w o m e n [F(4,44) = 4.17, p < 0.05]. Y o u n g e r w o m e n read at significantly higher S F F levels o n d a y 2 t h a n o n d a y s I a n d 3 (Table 3). A m o n g the m e n , n o significant differences were found for this variable [F(4,42) = 0.88, p > 0.05]. F o r the s p e a k i n g task, m e n e x h i b i t e d n o signifi-
TABLE 3. Means (M) and standard deviations (SD) for SFF (in Hz) and vocal intensity (in relative db) associated
with female speakers in with the three age groups across 3 days, three times a day for vowel production, reading, and speaking SFF Young Day Vowel ! 2 3 Time a.m. Noon p.m. Reading I 2 3 Time a.m. Noon p.m. Speaking 1 2 3 Time a.m. Noon p.m.
db
Middle-aged
Old
Young
Middle-aged
Old
M
SD
M
SD
M
SD
M
SD
M
SD
M
SD
206.74 210.13 206.74
25.88 32. I I 25.68
191.30 194.06 209.31
19.98 22.84 23.59
187.44 194.85 184.86
23.52 26.16 27.05
61.60 63.30 62.97
4.48 4.75 5.46
65.33 66.07 65.33
5.59 5.43 4.88
64.63 65.95 66.81
6.25 5.1 ! 4.63
203.46 207.97 215.37
29.93 27.52 29.65
194.00 200.59 200.09
21.90 24.57 23.56
190.68 191.26 185.09
25.88 24.57 22.79
61.90 62.77 63.20
4.94 4.95 4.93
64.85 65.67 66.22
4.66 5.88 5.26
64.50 65.48 67.55
5.89 5.88 3.69
194.91 196.96 190.26
19.42 21.18 18.05
190.50 197.07 194.64
17.13 15.77 15.12
164.31 172.29 172.79
25.58 15.74 16.26
64.57 65.07 64.37
2.54 2.78 2.73
67.07 67.30 66.48
3.67 3.57 3.06
69.80 69.05 71.19
4.25 3.15 4.80
194.17 193.33 196.64
22.38 19.17 17.73
194.56 192.78 194.87
16.90 15.98 15.79
170.09 167.39 172.30
14.30 25.48 18.14
63.87 64.93 65.20
2.58 2.84 2.48
66.93 67.00 66.93
3.48 3.21 3.67
69.57 69.86 70.65
4.15 4.17 4.27
189.96 188.64 187.00
21.59 20.34 21.57
183.83 186.66 188.24
12.97 13.05 13.13
173.78 176.53 174.54
14.91 14.54 15.39
63.83 63.53 63.00
2.81 2.45 3.04
66.30 66.81 65.96
3.55 3.55 3.45
67.50 67.33 68.76
3.68 3.30 5.28
186.33 186.63 192.64
21.16 20.46 21.40
183.11 185.83 189.80
14.97 12.41 10.95
171.68 177.97 175.28
13.70 16.24 14.22
63.37 64.17 62.83
2.78 2.53 2.92
68.48 66.70 65.89
4.18 2.77 3.74
67.95 67.33 68.35
4.76 4.14 3.64
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T A B L E 4. Means (M) and standard deviations (SD) f o r S F F (in Hz) and vocal intensity (in relative db) associated with male speakers in with the three age groups across 3 days and three times a day f o r vowel prodaction, reading, and speaking SFF Young Day
db
Middle-aged
Old
Young
Middle-aged
Old
M
SD
M
SD
M
SD
M
SD
M
SD
M
SD
Vowel 1 2 3
122.97 123.47 121.92
17.38 20.56 22.91
124.36 126.09 121.45
22.32 23.28 20.73
144.32 143.46 139.42
15.41 18.53 22.24
68.22 69.81 69.37
6.71 7.00 7.46
68.74 67.93 67.26
6.95 7.30 7.56
74.72 75.72 76.00
3.23 5.71 3.90
Time a.m. Noon p.m.
121.76 124.55 122.05
21.92 23.24 15.02
120.34 124.17 127.38
19.84 21.03 24.87
140.64 146.24 140.32
19.68 20.51 16.06
68.33 69.67 69.41
7.65 6.71 7.01
66.81 68.65 68.26
7.39 7.26 7.10
74.72 76.17 75.56
4.50 4.61 4.49
Reading I 2 3
137.31 137.43 136.91
9.52 7.64 16.65
134.28 135.07 135.19
17.09 30.41 17.20
140.13 136.17 141.01
10.89 6.73 10.04
67.74 67.70 67.85
3.85 3.04 3.60
68.74 67.59 67.67
3.73 3.50 2.97
74.94 75.83 75.39
3.15 2.67 3.93
Time a.m. Noon p.m.
137.86 136.77 136.99
10.45 6.22 7.47
133.78 135.01 135.73
16.63 16.59 18.90
135.69 141.67 139.76
8.92 9.89 8.90
66.89 68. I 1 68.30
3.31 3.41 3.63
67.26 68.48 68.26
3.32 3.49 3.43
74.78 75.89 75.50
3.12 3.89 2.73
Speaking 1 2 3
136.09 135.96 137.16
10.60 11.72 12.44
128.67 129.56 126.55
17.21 16.19 16.85
134.12 135.51 131.22
10.17 7.42 9.06
66.70 66.44 66.41
2.97 3.94 3.43
68.11 66.52 67.15
4.43 3.83 3.35
73.22 73.58 74.28
3.61 3.18 4.33
Time a.m. Noon p.m.
138.88 135.14 135.20
13.36 12.39 8.00
125.79 129.18 129.80
14.84 17.26 17.87
131.40 135.86 133.78
8.05 9.11 9.65
65.85 66.93 66.78
4.09 2.57 3.49
66.56 67.22 68.00
4.05 4.07 3.59
73.17 74.56 73.33
3.82 3.85 3.46
cant differences by day or time [F(4,84) = 0.63, p > 0.05]. However, women exhibited a significant day by time interaction [F(4,86) = 2.68, p < 0.05]. Women spoke the final speaking samples at higher SFF levels than they did initial ones on days 1 and 2, while on day 3, there were no significant differences among the sessions. Vocal intensity Overall, statistical analysis revealed that for all speech intensity tasks, the men spoke at significantly higher levels than did the women. When viewing variability of the vocal intensity data, as portrayed in Table 2, it can be seen that, for the most part, standard deviations are relatively small in comparison to the large values associated with the relative db. Whereas the mean vocal intensity across all three speaking conditions for both men and women ranged from 63 to 75 db, standard deviations ranged only from 1.7 to 3.8 db, with most (12 of 18) falling within the 2.0-3.0 db range. Moreover, the variability associated with the/a/productions, with the possible exception of the old women
(3.8 db) and young men (3.5 db), was generally similar to that associated with the reading and speaking samples, i.e., most falling in the 2.0 and 2.82 db range. As for statistically significant interactions associated with intensity data, several of note occurred for all three speaking conditions. For the vowel/o/, analysis revealed that men sustained the vowel at significantly louder levels than did women [F(1,42) = 14.91, p < 0.05]. As can be seen in Table 4, among the men, a significant time of recording effect [F(2,42) = 6.68, p < 0.05] occurred with the sound pressure level (SPL) of the second recording being higher than that of the first. Analysis of each recording session on each day revealed a significant age by day by time interaction [F(8,84) = 3.76, p < 0.05] among the women. Younger women exhibited significantly lower SPLs than did middle-aged and older women on day 3 and during the late afternoon recording. In addition, older women exhibited significant increases in SPLs across recording sessions on days 1 and 2; younger women also exhibited this pattern on day 1. Journal of Voice, Vol. 10, No. 3,
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W. S. B R O W N ET AL.
For reading samples, significant sex [F(1,43) = 12.49, p < 0.05], age [F(2,43) = 18.02, p < 0.05], and time [F(2,86) = 10.60, p < 0.05] main effects occurred. When comparing the data in Tables 3 and 4, it can be seen that men generally used significantly greater SPLs than did women. In addition, for both men and women, older subjects read at higher SPLs than did middle-aged and younger subjects (Tables 3 and 4). Finally, subjects used significantly greater SPLs during the last recording sessions of the days than they did during the first one. For speaking tasks, significant sex [F(1,43) = 13.38, p < 0.05] and age [F(2,43) = 16.74, p < 0.05] effects occurred. Younger women used significantly lower SPLs than the other subjects (Table 3), while older men used significantly greater SPLs than the other subjects (Table 4). As shown in Table 4, among the men, a significant time effect [F(2,42) = 3.26, p < 0.05] occurred. The second speaking samples, similar to reading samples, were spoken at greater SPLs than were the first ones. Analysis of each recording session from each day revealed a significant day by time of day interaction among the women [F(4,88) samples 2.57, p < 0.05]. The first and third speaking tasks were spoken with significantly greater SPLs than the second ones of the first day; however, this pattern was reversed on the second day. DISCUSSION AND CONCLUSIONS Previous investigators have suspected that when subjects are asked to set their own levels of oral output, they may be introducing an experimental variable--a variable that has received only little attention and one that has not been well documented. Thus, many investigators control the output of their experimental speakers with appropriate instrumentation, while others may simply accept this source of variability when they instruct their speakers to set their own vocal output, i.e., "comfortable" or "natural" level of speaking. When the present data associated with repeated utterances within and across days were analyzed statistically, both SFF and vocal intensity demonstrated the presence of significant variability (at the 0.05 level of confidence) as related to the sex and age of the speaker, and the type of speech sample. Some of this variability can be explained rather easily, as there are sufficient reports in the experimental literature to support such variability. For example, the fact that the women spoke at significantly Journal of Voice, Vol. 10, No. 3, 1996
higher levels for the SFF tasks than did the men was not at all surprising, as it has been well documented that such would be the case for any normal vocalized task (7-12). Moreover, it was found that, generally, the men spoke at significantly higher intensity levels in comparison to the women--a finding supported by some (13,14), but not others (1,15,16). Even certain of the within sex variability can be accounted for, as substantiated by experimental evidence. The fact that older women spoke at significantly lower SFF levels in comparison to young and middle-aged subjects has received recent verification (13), as has the present finding that the older men spoke at significantly higher SFF levels than their younger counterparts (14). And, finally, the finding that vowel data were substantially more variable in comparison to data for reading and speaking samples also has a reasonable explanation. Measurement of the fundamental frequency of a sustained vowel yields, basically, only one datum point, i.e., the average fundamental frequency over the time sampled. Measurement of connected speech, on the other hand, entails a "running" average of the variations that would be associated with "naturally" produced speech. In other words, since "running" speech leads to a measure of central tendency, one would expect single samples of vowels to vary more than multiple samples from speech. Some of the more isolated interactions are not as easy to explain, i.e., why on certain trials within days or across days were some subjects found to be higher or lower (SFF) or louder or softer? Many of these significant variations may be, simply, normal variations that were caught in the statistical manipulations. Yet, even with the complexity of the above statistical manipulations and significant outcomes of the data, when simply describing trends from group means and standard deviations, the variability that these normal speakers exhibited within days and across days for three types of vocal samples did not appear extensive and may represent tolerable limits of variation depending on the purpose of the measures. However, it must be noted that while variability in one or both measures may occur, group trends obtained at one sampling period may not reflect individual changes over multiple sampling periods. Indeed, the question becomes one of the amount of variability in SFF and vocal intensity the investigator is willing to tolerate before deciding whether
C O M F O R T A B L E E F F O R T L E V E L REVISITED
to use external devices to control such parameters or to simply instruct subjects to produce speech samples in a "comfortable" manner. Not only will normal speakers vary in their vocal production of these vocal parameters from one experimental session to the next, but also the observed patterns of variation tend to be idiosyncratic to each individual speaker. Moreover, as was seen in the present data, this variability will also fluctuate in association with the type of speaking, i.e., sustained vowel productions are more variable within as well as across sessions in comparison to reading or speaking. In reviewing these data, as well as the results of the previous investigations (1-4), differences that occur across experimental sessions reflect statistically significant differences despite small absolute differences. Thus, future experimenters must expect some variability to occcur and design their experiments accordingly. With this in mind, since vowel productions appear to be the most variable in comparison to reading and extended speaking, the present authors recommend that, for determining SFF, investigators use a standard reading passage or extemporaneous speaking, where the instructions permit the speaker to set his/her own "comfortable" level. Sustained phonation should be reserved for conditions in which the investigator desires to examine the mucal wave pattern, identify tremor rates, or measure maximum phonation time. Based on the present results, one can expect ----10 Hz of variability in SFF for group reading samples, which translates to ----I semitone. One can expect -+--2 db SPL group variation in vocal intensity from any one experimental session to the next. This group variability agrees with that reported by Brown et al. (1) and Garrett and Healey (2) for both SFF and vocal intensity and is somewhat <2.74 semitone average variation over a 30-day period reported by Coleman and Markham (4). For reading or speaking samples, elderly speakers appear to be only slightly more variable than younger speakers, with no appreciable difference related to gender. Whereas these data were derived from healthy, normal speakers, generalization to clinical populations for whom little is known with regard to frequency or intensity variations may not be valid. The fact remains that variability in vocal output in abnormal populations cannot be assumed to be more,
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less, or the same as that of normals. Rather, variability should be examined with relation to the pathophysiology of abnormal speaking populations. Even among the normal groups examined herein, there were individuals who exhibited extensive variation, a factor that may warrant consideration when large subject groups are sampled or when sampling is done across voice disorders and diseases. REFERENCES I. Brown WS, Murry T, Hughes D. Comfortable effort level: an experimental variable. J Acoust Soc Am 1976;60:696-700. 2. Garrett KL, Healey EC. An acoustic analysis of fluctuations in the voices of normal adult speakers across three times a day. J Acoust Soc Am 1987;82:58--62. 3. Nittrouer S, McGowan RS, Milenkovic P, Beehler D. Acoustic measurements of men's and women's voices: a study of context effects and covariation. J Speech Hearing Res 1990;33:761-75. 4. Coleman RF, Markham IW. Normal variations in habitual pitch. J Voice 1991 ;5:173-7. 5. Fairbanks G. Voice and articulated drill book. New York: Harper and Brothers, 1960. 6. Hollien H. Analog instrumentation for acoustic speech analysis. In: John K. Darby, ed. Speech evaluation in psychiatO'. New York: Grune and Stratton, 1981. 7. Fairbanks G, Wiley J, Lassman F. An acoustical study of vocal pitch in seven- and eight-year old boys. Child Dev 1949;20:63-9. 8. Fairbanks G, Herbert E, Hammond J. An acoustic study of vocal pitch in seven- and eight-year old girls. Child Dev 1949;20:71-8. 9. Hollien H, Malcik E. Evaluation of cross-sectional studies of adolescent voice change in males. Speech Monogr 1967;34: 80--4. 10. Hollien H, Paul P. A second evaluation of the speaking fundamental characteristics of post-adolescent girls. Lang Speech 1969; 12:119-24. I1. Snidicor J. A comparative study of the pitch and duration characteristics of impromptu speaking and oral reading. Speech Monogr 1943;10:50--6. 12. Brown WS, Morris R, Hollien H, Howell E. Speaking fundamental frequency characteristics as a function of age and professional singing. J Voice 1991;5:310-5. 13. Brown WS, Morris R, Hicks D, Howell E. Phonational profiles of female professional singers and nonsingers. J Voice 1993;7:21%26. 14. Morris R, Brown WS, Hicks D, Howell E. Phonational profiles of male professional singers and nonsingers. J Voice (in press). 15. Brown WS, McGlone R. Aerodynamic and acoustic study of stress in sentence productions. J Acoust Soc Am 1974;56: 971-4. 16. Murry T, Brown WS. Short term consistency of vocal utterances. Transcripts o f the Eleventh Symposium on the Care o f the Professional Voice. New York City, NY: The Voice Foundation, 1982:16-24.
Journal of Voice, I/ol. 10. No. 3, 1996
V~I. 10, No. 3, pp. 299-305 © 1996 Lippincott-Raven Publishers, Philadelphia
Comfortable Effort Level Revisited W. S. Brown, Jr., *Richard J. Morris, and tThomas Murry Institute for Advanced Study of the Communication Processes, University of Florida, Gainesville, Florida; *Department of Communication Disorders, Florida State University, Tallahassee, Florida; and "~Department of Otolaryngology, University of Tennessee, College of Medicine, Memphis, Tennessee, U.S.A.
Summary: The purpose of this study was to measure the variability of frequency and intensity of speech, using multiple voice samples obtained over a period of time at a speaker's "comfortable effort level." Variability in vocal output within and across several experimental sessions was assessed from measures of speaking fundamental frequency (SFF) and vocal intensity for utterances repeated three times a day over a 3-day period. Three distinct age groups of men and women--young, middle-aged and elderly--repeated the vowel/o/, read a standard passage, and spoke extemporaneously during each experimental session. Results indicated that variability in SFF and intensity were present across experimental sessions, age groups, gender, and speaking samples. Generally, group means indicated that ---+1 semitone of variability for SFF and - 2 db sound pressure level (SPL) variation in vocal intensity from any one experimental session to the next could be expected; individual variations within any group may reach two semitones and 6 db SPL. Key Words: Comfortable effort--Comfortable effort level--Effort level--Vocal effort.
In an effort to examine laryngeal behavior under normal speaking conditions, experimenters often ask subjects to repeat vocal utterances at a " c o m fortable effort level." When experimenters refer to " c o m f o r t a b l e " , they are usually specifying, operationally, the level of effort that is expended by a speaker as reflected by such vocal parameters as fundamental f r e q u e n c y and/or intensity. The term " c o m f o r t a b l e effort l e v e l " and analogous terms such as " h a b i t u a l " and " n a t u r a l " , imply that there is a level of vocal or speech output, or " e f f o r t " , which, for a speaker, is typical when repeating an utterance. It may be hypothesized that instructions to produce a sample o f speech in a comfortable
manner do not place regulations on a subject's vocal output as do external controls, for which the speaker's output is monitored according to the experimenter's specifications. When external controls are placed on the s p e a k e r ' s output, the experimenter uses specific instrumentation to be assured that the subject is producing the particularly desired response. When speakers set their own level of vocal output at their " c o m f o r t a b l e " or " n a t u r a l " mode, there is no assurance that the subjects will use the same frequency/intensity parameters o v e r repeated sampling periods. The present authors, nearly 20 years ago, presented data directly related to the vocal variability associated with experimental instructions to produce s p e e c h samples at a " c o m f o r t a b l e e f f o r t level" (1). Since that time, several other reports of vocal variability have appeared in the research literature (2-4). Results of the reported studies indicated, generally, that vocal output did vary from one experimental session to the next when subjects were instructed to produce the vocal samples in a
Accepted March 23, 1995. Address correspondence and reprint requests to Dr. W. S. Brown, Jr. at Institute for Advanced Study of the Communication Processes, 63 Dauer Hall, University of Florida, Gainesville, FL 32611, U.S.A. Results of this study were presented at the 22nd Annual Symposium, Care of the Professional Voice, Philadelphia, PA, U.S.A. June 9, 1993.
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W. S. B R O W N ET AL.
comfortable manner. More importantly, given that variability of vocal output at comfortable effort does exist, it remains to be determined if this variability represents a significant compromise to voice sampling or whether sampling one's comfortable effort should be eliminated from single sampling studies. Results of the present investigators' study reported in 1976 (1) revealed that across 5 successive days, for the production of sustained vowels and short phrases, the majority of speakers were relatively stable in their utterances across sessions. However, individual speakers were found to vary as much as 4 semitones, or - 2 0 Hz, across the 5-day period. More recently, in 1987, Garrett and Healey (2) reported that a group of men exhibited significant within-speaker changes in speaking fundamental frequency (SFF) from morning to noon to late afternoon, whereas their female counterparts revealed no significant changes across recording sessions. Contrarily, in 1990, Nittrouer et al. (3) reported that SFF was not affected by the time of day in which the measures are taken. They reported no significant differences in SFF for either men or women when vocal utterances were compared for the early morning versus late afternoon. In 1991, Coleman and Markham (4) concluded that, in adult talkers, habitual pitch appears to be a stable measurement that varies a relatively small amount over a month, a year, or, even a decade. They viewed their finding of a 2.74 semitone average variation in SFF for a group of normal young women over a 30-day period to be clinically acceptable. Coleman and Markham also pointed out that this average variation may or may not be acceptable for other, nonclinical purposes. PURPOSE The use of comfortable effort level has relevance to voice scientists, speech pathologists, physicians, and voice teachers alike, as each has specific interests in knowing the variability that exists in a speaker's vocal utterances. This study was designed to revisit the issue of vocal variability. The purpose was to obtain measures of SFF and vocal intensity at the comfortable effort level in order to assess the degree of variability in vocal output across utterance types and recording sessions. Unlike previous studies, which have focused either on the speech material or the variation across sessions, the present study includes measures of SFF and vocal Journal of Voice, Vol. I0, No. 3, 1996
intensity for utterances repeated over a 3-day period and at three different time periods of each day. Moreover, this study expands the speaker population to include men and women representing three distinct age groups-young, middle-aged, and old. METHODS The subjects of this study were 50 untrained speakers divided into three age groups: nine men (range, 21-33 years of age) and 10 women (range, 20-22 years) in the 20-35 year age range (young); nine men (range, 40-54 years of age) and nine women (range, 42-50 years of age) in the 40-55 year age range (middle-aged); and six men (range, 69-87 years of age) and seven women (range, 65-89 years of age) who were/>65 years (old). All subjects were in good health and it was agreed by both subjects and experimenters that subjects had normal speech and hearing for their age group. None of the subjects reported any neurological or respiratory problems or diseases, nor did they report any common illnesses (i.e., colds or flu) during the week of recording which may have had a temporary effect on vocal output. Each subject was seated in a noise-free environment at a constant mouth-to-microphone distance of I0 in. For each experimental session, subjects were asked to phonate the v o w e l / a / f o r 10 s, read the first paragraph of the Rainbow Passage (5), and speak extemporaneously for 30 s, prompted by a picture that was different for each experimental session. The only prior instruction given to subjects for each of the three speaking samples was to produce the sample at a comfortable effort level. Each subject's utterances were recorded on audio tape (Shure Microphone, 545SD coupled to a Teac X300R tape recorder). Speech samples were produced three times during a l-week time frame three times daily: once in the morning between 8:00 and 10:00 a.m., once in the early afternoon between 12:00 and 2:00 p.m., and once in the late afternoon between 4:00 and 6:00 p.m. Prior to each recording session, a calibration tone of I000 Hz at 74 db, via a Wavetek 133 function generator and presented through a loudspeaker placed 10 in from the microphone, was recorded on the tape. This calibration tone served as the reference from which to calculate vocal intensity in relative db. The calibration tone was also used to verify playback tape speed for each recording session. To determine average SFF, tape recorded utter-
COMFORTABLE EFFORT LEVEL REVISITED ances were analyzed by means of FFI-8, the current version of the IASCP Fundamental Frequency Indicator (6). Processing by this method yielded the mean SFF in Hz and semitones (reference = 16.35159). Relative vocal intensity was determined by playing the tape recorded utterances of the vowel, the second sentence of the Rainbow Passage and - 3 s of the extemporaneous speech sample through a Bruel and Kjaer graphic level recorder at a writing speed (slew rate) of 250 mm/s and paper speed of 30 mm/s. Each reading and speaking sample produced 14-16 energy peaks, which were measured in relative db and averaged. The average value represented mean (relative) vocal intensity for each sample utterance. And, finally, a repeated measures analysis of variance (ANOVA) (by sex by day by time) was applied to the data to determine statistical significance at the 0.05 confidence level. Separate ANOVAs were determined for each task--sustained vowel, oral reading, and spontaneous speaking, as well as for SFF and intensity--resulting in a total of six ANOVAs. RESULTS Tables 1 and 2 have been simplified by collapsing the data over days and times of day, presenting group means and standard deviations for each age group and speaking condition. The data in these two tables are exemplary of some of the more obvious trends associated with the variability exhibited by these groups of speakers. Even though Table 1 presents the SFF data in both Hz and semitones, the semitone data will prevail as the primary indicator of group variability. This treatment of the data is more traditional as fundamental frequency is logarithmic and, thus, the use of the semitone measure
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allows for a more valid comparison of male and female voices, which tend to be an octave apart on the musical scale. Tables 3 and 4 present the reader with the mean SFF and average vocal intensity data for men and women, associated with the three speaking conditions for each of the 3 days and for each of the times of day across the three age groups. The data in these two tables give the reader a broader view of the overall distribution of within- and betweengroup variabilities and also can be referred to in relation to the statistical treatment of the data. SFF Overall, statistical analysis revealed that for all tasks, women, as would be expected, spoke at significantly higher levels than did men. As can be seen in Table 1, in most cases the highest variability in SFF occurred for the vowel productions, with standard deviations ranging from 1.0 to 1.7 semitones. In comparison, reading and speaking productions generally exhibited smaller standard deviations, ranging from 0.6 to 1.3 semitones. Moreover, the 65-89 year old group, especially the women, demonstrated somewhat more variability in vowel productions in comparison to that associated with their younger counterparts. This was not the case for reading and speaking conditions, however, in which the semitone standard deviations were essentially comparable within gender groups. Across age groups and across all speaking conditions, men appeared to be somewhat more variable than women. Several interactions for all three speaking conditions are worth noting. For sustained productions, analysis revealed a significant age by sex by day interaction [F(6,82) = 2.74, p < 0.05]. The data indicated that older women spoke at significantly
T A B L E 1. Group means (M) and standard deviations (SD) collapsed across days and times of day associated with
SFF reported in Hz (and semitones) for each of the three age groups and speaking samples Vowel Subjects
Reading
Speaking
M
SD
M
SD
M
SD
Women Young Middle-aged Old
209 (44) 198 (43) 189 (42)
12 (I.0) 14 (!.2) 18 (I.7)
195 (43) 194 (43) 170 (41)
10 (0.9) 10 (0.9) 9 (0.6)
189 (42) 186 (42) 175 (41)
9 (0.8) 9 (0.9) 9 (0.8)
Men Young Middle-aged Old
123 (35) 124 (35) 142 (37)
I1 (I.4) 9 (I.3) 15 (I.5)
137 (37) 135 (36) 139 (37)
6 (1.3) 7 (1.0) 7 (0.9)
136 (37) 128 (36) 134 (36)
9 (1.1) 7 (0.9) 8 (1.1)
Journal of Voice, Vol. 10, No. 3, 1996
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W. S. B R O W N E T A L .
TABLE 2. Group means (M) and standard deviations (SD) collapsed across days and times of day associated with
vocal intensity (in relative db) for each of the three age groups and speaking samples Vowel Su~ects Women Young Middle-aged Old Men Young Middle-aged Old
Reading
Speaking
M
SD
M
SD
M
SD
63 66 66
2.7 2.3 3.8
65 67 70
1.9 1.7 2.2
63 66 68
2.3 2.3 2.4
66 68 75
3.5 2.8 3.2
68 68 75
1.9 2. I 2.3
67 67 74
2.5 2.4 2.6
l o w e r S F F levels t h a n did the y o u n g a n d m i d d l e aged w o m e n o n d a y 3 (Table 3), while o l d e r m e n s p o k e at s i g n i f i c a n t l y h i g h e r S F F levels t h a n did y o u n g a n d m i d d l e aged m e n o n all 3 d a y s (Table 4). A m o n g the w o m e n , a significant age by d a y intera c t i o n [F(4,40) = 5.04, p < 0.05] o c c u r r e d . M i d d l e aged w o m e n s p o k e at h i g h e r S F F levels o n d a y 3, while y o u n g e r a n d o l d e r w o m e n e x h i b i t e d no sign i f i c a n t d i f f e r e n c e a c r o s s d a y s (Table 3). F o r the m e n , n o significant d i f f e r e n c e s o c c u r r e d for S F F a c r o s s d a y s w i t h i n the age g r o u p s . F o r r e a d i n g , a significant age b y sex S F F inter-
a c t i o n o c c u r r e d [F(2,43) = 3.85, p < 0.05]. O l d e r w o m e n read at s i g n i f i c a n t l y l o w e r f r e q u e n c i e s t h a n did y o u n g e r a n d m i d d l e - a g e d w o m e n for all s e s s i o n s ( T a b l e 3), while m e n did n o t differ s i g n i f i c a n t l y a m o n g age g r o u p s ( T a b l e 4). M o r e o v e r , a s i g n i f i c a n t age b y d a y i n t e r a c t i o n was f o u n d a m o n g the w o m e n [F(4,44) = 4.17, p < 0.05]. Y o u n g e r w o m e n read at significantly higher S F F levels o n d a y 2 t h a n o n d a y s I a n d 3 (Table 3). A m o n g the m e n , n o significant differences were found for this variable [F(4,42) = 0.88, p > 0.05]. F o r the s p e a k i n g task, m e n e x h i b i t e d n o signifi-
TABLE 3. Means (M) and standard deviations (SD) for SFF (in Hz) and vocal intensity (in relative db) associated
with female speakers in with the three age groups across 3 days, three times a day for vowel production, reading, and speaking SFF Young Day Vowel ! 2 3 Time a.m. Noon p.m. Reading I 2 3 Time a.m. Noon p.m. Speaking 1 2 3 Time a.m. Noon p.m.
db
Middle-aged
Old
Young
Middle-aged
Old
M
SD
M
SD
M
SD
M
SD
M
SD
M
SD
206.74 210.13 206.74
25.88 32. I I 25.68
191.30 194.06 209.31
19.98 22.84 23.59
187.44 194.85 184.86
23.52 26.16 27.05
61.60 63.30 62.97
4.48 4.75 5.46
65.33 66.07 65.33
5.59 5.43 4.88
64.63 65.95 66.81
6.25 5.1 ! 4.63
203.46 207.97 215.37
29.93 27.52 29.65
194.00 200.59 200.09
21.90 24.57 23.56
190.68 191.26 185.09
25.88 24.57 22.79
61.90 62.77 63.20
4.94 4.95 4.93
64.85 65.67 66.22
4.66 5.88 5.26
64.50 65.48 67.55
5.89 5.88 3.69
194.91 196.96 190.26
19.42 21.18 18.05
190.50 197.07 194.64
17.13 15.77 15.12
164.31 172.29 172.79
25.58 15.74 16.26
64.57 65.07 64.37
2.54 2.78 2.73
67.07 67.30 66.48
3.67 3.57 3.06
69.80 69.05 71.19
4.25 3.15 4.80
194.17 193.33 196.64
22.38 19.17 17.73
194.56 192.78 194.87
16.90 15.98 15.79
170.09 167.39 172.30
14.30 25.48 18.14
63.87 64.93 65.20
2.58 2.84 2.48
66.93 67.00 66.93
3.48 3.21 3.67
69.57 69.86 70.65
4.15 4.17 4.27
189.96 188.64 187.00
21.59 20.34 21.57
183.83 186.66 188.24
12.97 13.05 13.13
173.78 176.53 174.54
14.91 14.54 15.39
63.83 63.53 63.00
2.81 2.45 3.04
66.30 66.81 65.96
3.55 3.55 3.45
67.50 67.33 68.76
3.68 3.30 5.28
186.33 186.63 192.64
21.16 20.46 21.40
183.11 185.83 189.80
14.97 12.41 10.95
171.68 177.97 175.28
13.70 16.24 14.22
63.37 64.17 62.83
2.78 2.53 2.92
68.48 66.70 65.89
4.18 2.77 3.74
67.95 67.33 68.35
4.76 4.14 3.64
Journal of Voice, Vol. 10, No. 3. 1996
C O M F O R T A B L E E F F O R T L E V E L REVISITED
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T A B L E 4. Means (M) and standard deviations (SD) f o r S F F (in Hz) and vocal intensity (in relative db) associated with male speakers in with the three age groups across 3 days and three times a day f o r vowel prodaction, reading, and speaking SFF Young Day
db
Middle-aged
Old
Young
Middle-aged
Old
M
SD
M
SD
M
SD
M
SD
M
SD
M
SD
Vowel 1 2 3
122.97 123.47 121.92
17.38 20.56 22.91
124.36 126.09 121.45
22.32 23.28 20.73
144.32 143.46 139.42
15.41 18.53 22.24
68.22 69.81 69.37
6.71 7.00 7.46
68.74 67.93 67.26
6.95 7.30 7.56
74.72 75.72 76.00
3.23 5.71 3.90
Time a.m. Noon p.m.
121.76 124.55 122.05
21.92 23.24 15.02
120.34 124.17 127.38
19.84 21.03 24.87
140.64 146.24 140.32
19.68 20.51 16.06
68.33 69.67 69.41
7.65 6.71 7.01
66.81 68.65 68.26
7.39 7.26 7.10
74.72 76.17 75.56
4.50 4.61 4.49
Reading I 2 3
137.31 137.43 136.91
9.52 7.64 16.65
134.28 135.07 135.19
17.09 30.41 17.20
140.13 136.17 141.01
10.89 6.73 10.04
67.74 67.70 67.85
3.85 3.04 3.60
68.74 67.59 67.67
3.73 3.50 2.97
74.94 75.83 75.39
3.15 2.67 3.93
Time a.m. Noon p.m.
137.86 136.77 136.99
10.45 6.22 7.47
133.78 135.01 135.73
16.63 16.59 18.90
135.69 141.67 139.76
8.92 9.89 8.90
66.89 68. I 1 68.30
3.31 3.41 3.63
67.26 68.48 68.26
3.32 3.49 3.43
74.78 75.89 75.50
3.12 3.89 2.73
Speaking 1 2 3
136.09 135.96 137.16
10.60 11.72 12.44
128.67 129.56 126.55
17.21 16.19 16.85
134.12 135.51 131.22
10.17 7.42 9.06
66.70 66.44 66.41
2.97 3.94 3.43
68.11 66.52 67.15
4.43 3.83 3.35
73.22 73.58 74.28
3.61 3.18 4.33
Time a.m. Noon p.m.
138.88 135.14 135.20
13.36 12.39 8.00
125.79 129.18 129.80
14.84 17.26 17.87
131.40 135.86 133.78
8.05 9.11 9.65
65.85 66.93 66.78
4.09 2.57 3.49
66.56 67.22 68.00
4.05 4.07 3.59
73.17 74.56 73.33
3.82 3.85 3.46
cant differences by day or time [F(4,84) = 0.63, p > 0.05]. However, women exhibited a significant day by time interaction [F(4,86) = 2.68, p < 0.05]. Women spoke the final speaking samples at higher SFF levels than they did initial ones on days 1 and 2, while on day 3, there were no significant differences among the sessions. Vocal intensity Overall, statistical analysis revealed that for all speech intensity tasks, the men spoke at significantly higher levels than did the women. When viewing variability of the vocal intensity data, as portrayed in Table 2, it can be seen that, for the most part, standard deviations are relatively small in comparison to the large values associated with the relative db. Whereas the mean vocal intensity across all three speaking conditions for both men and women ranged from 63 to 75 db, standard deviations ranged only from 1.7 to 3.8 db, with most (12 of 18) falling within the 2.0-3.0 db range. Moreover, the variability associated with the/a/productions, with the possible exception of the old women
(3.8 db) and young men (3.5 db), was generally similar to that associated with the reading and speaking samples, i.e., most falling in the 2.0 and 2.82 db range. As for statistically significant interactions associated with intensity data, several of note occurred for all three speaking conditions. For the vowel/o/, analysis revealed that men sustained the vowel at significantly louder levels than did women [F(1,42) = 14.91, p < 0.05]. As can be seen in Table 4, among the men, a significant time of recording effect [F(2,42) = 6.68, p < 0.05] occurred with the sound pressure level (SPL) of the second recording being higher than that of the first. Analysis of each recording session on each day revealed a significant age by day by time interaction [F(8,84) = 3.76, p < 0.05] among the women. Younger women exhibited significantly lower SPLs than did middle-aged and older women on day 3 and during the late afternoon recording. In addition, older women exhibited significant increases in SPLs across recording sessions on days 1 and 2; younger women also exhibited this pattern on day 1. Journal of Voice, Vol. 10, No. 3,
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W. S. B R O W N ET AL.
For reading samples, significant sex [F(1,43) = 12.49, p < 0.05], age [F(2,43) = 18.02, p < 0.05], and time [F(2,86) = 10.60, p < 0.05] main effects occurred. When comparing the data in Tables 3 and 4, it can be seen that men generally used significantly greater SPLs than did women. In addition, for both men and women, older subjects read at higher SPLs than did middle-aged and younger subjects (Tables 3 and 4). Finally, subjects used significantly greater SPLs during the last recording sessions of the days than they did during the first one. For speaking tasks, significant sex [F(1,43) = 13.38, p < 0.05] and age [F(2,43) = 16.74, p < 0.05] effects occurred. Younger women used significantly lower SPLs than the other subjects (Table 3), while older men used significantly greater SPLs than the other subjects (Table 4). As shown in Table 4, among the men, a significant time effect [F(2,42) = 3.26, p < 0.05] occurred. The second speaking samples, similar to reading samples, were spoken at greater SPLs than were the first ones. Analysis of each recording session from each day revealed a significant day by time of day interaction among the women [F(4,88) samples 2.57, p < 0.05]. The first and third speaking tasks were spoken with significantly greater SPLs than the second ones of the first day; however, this pattern was reversed on the second day. DISCUSSION AND CONCLUSIONS Previous investigators have suspected that when subjects are asked to set their own levels of oral output, they may be introducing an experimental variable--a variable that has received only little attention and one that has not been well documented. Thus, many investigators control the output of their experimental speakers with appropriate instrumentation, while others may simply accept this source of variability when they instruct their speakers to set their own vocal output, i.e., "comfortable" or "natural" level of speaking. When the present data associated with repeated utterances within and across days were analyzed statistically, both SFF and vocal intensity demonstrated the presence of significant variability (at the 0.05 level of confidence) as related to the sex and age of the speaker, and the type of speech sample. Some of this variability can be explained rather easily, as there are sufficient reports in the experimental literature to support such variability. For example, the fact that the women spoke at significantly Journal of Voice, Vol. 10, No. 3, 1996
higher levels for the SFF tasks than did the men was not at all surprising, as it has been well documented that such would be the case for any normal vocalized task (7-12). Moreover, it was found that, generally, the men spoke at significantly higher intensity levels in comparison to the women--a finding supported by some (13,14), but not others (1,15,16). Even certain of the within sex variability can be accounted for, as substantiated by experimental evidence. The fact that older women spoke at significantly lower SFF levels in comparison to young and middle-aged subjects has received recent verification (13), as has the present finding that the older men spoke at significantly higher SFF levels than their younger counterparts (14). And, finally, the finding that vowel data were substantially more variable in comparison to data for reading and speaking samples also has a reasonable explanation. Measurement of the fundamental frequency of a sustained vowel yields, basically, only one datum point, i.e., the average fundamental frequency over the time sampled. Measurement of connected speech, on the other hand, entails a "running" average of the variations that would be associated with "naturally" produced speech. In other words, since "running" speech leads to a measure of central tendency, one would expect single samples of vowels to vary more than multiple samples from speech. Some of the more isolated interactions are not as easy to explain, i.e., why on certain trials within days or across days were some subjects found to be higher or lower (SFF) or louder or softer? Many of these significant variations may be, simply, normal variations that were caught in the statistical manipulations. Yet, even with the complexity of the above statistical manipulations and significant outcomes of the data, when simply describing trends from group means and standard deviations, the variability that these normal speakers exhibited within days and across days for three types of vocal samples did not appear extensive and may represent tolerable limits of variation depending on the purpose of the measures. However, it must be noted that while variability in one or both measures may occur, group trends obtained at one sampling period may not reflect individual changes over multiple sampling periods. Indeed, the question becomes one of the amount of variability in SFF and vocal intensity the investigator is willing to tolerate before deciding whether
C O M F O R T A B L E E F F O R T L E V E L REVISITED
to use external devices to control such parameters or to simply instruct subjects to produce speech samples in a "comfortable" manner. Not only will normal speakers vary in their vocal production of these vocal parameters from one experimental session to the next, but also the observed patterns of variation tend to be idiosyncratic to each individual speaker. Moreover, as was seen in the present data, this variability will also fluctuate in association with the type of speaking, i.e., sustained vowel productions are more variable within as well as across sessions in comparison to reading or speaking. In reviewing these data, as well as the results of the previous investigations (1-4), differences that occur across experimental sessions reflect statistically significant differences despite small absolute differences. Thus, future experimenters must expect some variability to occcur and design their experiments accordingly. With this in mind, since vowel productions appear to be the most variable in comparison to reading and extended speaking, the present authors recommend that, for determining SFF, investigators use a standard reading passage or extemporaneous speaking, where the instructions permit the speaker to set his/her own "comfortable" level. Sustained phonation should be reserved for conditions in which the investigator desires to examine the mucal wave pattern, identify tremor rates, or measure maximum phonation time. Based on the present results, one can expect ----10 Hz of variability in SFF for group reading samples, which translates to ----I semitone. One can expect -+--2 db SPL group variation in vocal intensity from any one experimental session to the next. This group variability agrees with that reported by Brown et al. (1) and Garrett and Healey (2) for both SFF and vocal intensity and is somewhat <2.74 semitone average variation over a 30-day period reported by Coleman and Markham (4). For reading or speaking samples, elderly speakers appear to be only slightly more variable than younger speakers, with no appreciable difference related to gender. Whereas these data were derived from healthy, normal speakers, generalization to clinical populations for whom little is known with regard to frequency or intensity variations may not be valid. The fact remains that variability in vocal output in abnormal populations cannot be assumed to be more,
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less, or the same as that of normals. Rather, variability should be examined with relation to the pathophysiology of abnormal speaking populations. Even among the normal groups examined herein, there were individuals who exhibited extensive variation, a factor that may warrant consideration when large subject groups are sampled or when sampling is done across voice disorders and diseases. REFERENCES I. Brown WS, Murry T, Hughes D. Comfortable effort level: an experimental variable. J Acoust Soc Am 1976;60:696-700. 2. Garrett KL, Healey EC. An acoustic analysis of fluctuations in the voices of normal adult speakers across three times a day. J Acoust Soc Am 1987;82:58--62. 3. Nittrouer S, McGowan RS, Milenkovic P, Beehler D. Acoustic measurements of men's and women's voices: a study of context effects and covariation. J Speech Hearing Res 1990;33:761-75. 4. Coleman RF, Markham IW. Normal variations in habitual pitch. J Voice 1991 ;5:173-7. 5. Fairbanks G. Voice and articulated drill book. New York: Harper and Brothers, 1960. 6. Hollien H. Analog instrumentation for acoustic speech analysis. In: John K. Darby, ed. Speech evaluation in psychiatO'. New York: Grune and Stratton, 1981. 7. Fairbanks G, Wiley J, Lassman F. An acoustical study of vocal pitch in seven- and eight-year old boys. Child Dev 1949;20:63-9. 8. Fairbanks G, Herbert E, Hammond J. An acoustic study of vocal pitch in seven- and eight-year old girls. Child Dev 1949;20:71-8. 9. Hollien H, Malcik E. Evaluation of cross-sectional studies of adolescent voice change in males. Speech Monogr 1967;34: 80--4. 10. Hollien H, Paul P. A second evaluation of the speaking fundamental characteristics of post-adolescent girls. Lang Speech 1969; 12:119-24. I1. Snidicor J. A comparative study of the pitch and duration characteristics of impromptu speaking and oral reading. Speech Monogr 1943;10:50--6. 12. Brown WS, Morris R, Hollien H, Howell E. Speaking fundamental frequency characteristics as a function of age and professional singing. J Voice 1991;5:310-5. 13. Brown WS, Morris R, Hicks D, Howell E. Phonational profiles of female professional singers and nonsingers. J Voice 1993;7:21%26. 14. Morris R, Brown WS, Hicks D, Howell E. Phonational profiles of male professional singers and nonsingers. J Voice (in press). 15. Brown WS, McGlone R. Aerodynamic and acoustic study of stress in sentence productions. J Acoust Soc Am 1974;56: 971-4. 16. Murry T, Brown WS. Short term consistency of vocal utterances. Transcripts o f the Eleventh Symposium on the Care o f the Professional Voice. New York City, NY: The Voice Foundation, 1982:16-24.
Journal of Voice, I/ol. 10. No. 3, 1996