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Speaking Fundamental Frequency in Monozygotic and Dizygotic Twins
Journal of Voice Vol. 16, No. 4, pp. 466–471 © 2002 The Voice Foundation
Speaking Fundamental Frequency in Monozygotic and Dizygotic Twins Frans Debruyne, Wivine Decoster, Annemie Van Gijsel, and Julie Vercammen Experimental Otorhinolaryngology, University of Leuven, Belgium
Summary: The speaking fundamental frequency (SFF) and the intraindividual variation of the SFF during the reading of a Dutch standard text were measured in 30 female monozygotic twins (MT) and 30 dizygotic twins (DT), aged 15–29 years. A control group was created that consisted of 30 nonrelated paired individuals of equal age. Studying the intrapair correlation coefficients it seemed that the SFF was similar to a greater degree in MT and to a lesser degree in DT, while there was no correlation at all in nonrelated peers. These results are compatible with a genetic basis for the SFF. On the other hand, the intraindividual variation of the SFF was highly similar in MT and in DT (but not in nonrelated peers), so that for this parameter it was not possible to discern the influences of genetic disposition and shared environment. Key Words: Twin voice—Speaking fundamental frequency.
not genetically related to the twin; they obtained a correct identification of 82%, which is significantly more than by chance (33%). Besides these perceptive studies, investigators have measured and compared various acoustic characteristics of twin voices. One of the first parameters reported in this context was the vocal range in semitones, which was found to be very similar, especially in monozygotic twins.4,5 Flach6 measured the vocal range in 10 monozygotic twins and reported an identical range in eight pairs and a difference of one semitone in two pairs. Later, various objective acoustic measures in the frequency and time domain were studied. Similarities of the speaking fundamental frequency (SFF) in MT have been reported by Schilling,5 Gedda1 and Cornut.2 Przybyla7 examined the SFF of monozygotic and dizygotic twins and found an intrapair correlation coefficient of 0.539 for monozygotic twins and 0.338 for dizygotic twins, after correction for age and weight. More recently, Fuchs8 performed a statistical
INTRODUCTION Because twins resemble each other in many aspects, one expects that their voices also may sound similar at least to a certain degree. This expectation seems verified in daily life, when it can be hard to determine which member of a twin is speaking on the telephone. Studies with listeners have confirmed this perceptive similarity. It has been observed that twins themselves have difficulties identifying their own voices when presented recordings, in random order, of their own voice and the voice of their twin.1,2 Decoster et al 3 asked listeners to identify twin voices within voice trios. Each of these trios was randomly assembled by the two voices of a female twin and a third voice of another, age-matched woman who was Accepted for publication June 11, 2002 Address correspondence and reprint requests to Prof. F. Debruyne, Otorhinolaryngology—Head and Neck Surgery, U.Z. St. Rafaël, Kapucijnenvoer 33, 3000 Leuven, Belgium e-mail: [email protected]
466
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS study in a larger group of subjects (31 monozygotic twins) and found that the SFF is an acoustic feature which is significantly more similar in monozygotic twins than in nonrelated persons. Furthermore, various studies also concerned resonance-related characteristics. It was found that the number of harmonics and the general form of the frequency spectrum may be more similar in monozygotic twins compared with dizygotic twins1,6 or with pairs of nonrelated persons.8 Also Forrai and Gordos9 reported a positive correlation between similarity of spectral characteristics and monozygosy versus dizygosy. In contrast, Ostwald10 found no significant similarity when examining spectograms of the infant cry of 16 twin pairs (during the first month of life). In our investigation we studied two characteristics of the vocal fundamental frequency: the average fundamental frequency (speaking fundamental frequency, or “SFF”) and the intraindividual variation of the fundamental frequency (“varSFF”), both during the reading of a standard text. The aim of the investigation was (1) to study if twin voices are similar to each other concerning this parameters (if positive, one can speculate that these parameters could contribute to the fact that listeners perceive twin voices as similar), and (2) to study to what extent the observed similarity is genetically determined, by comparing the results in monozygotic twins (MT) with the results in dizygotic twins (DT). MT have a completely identical genotype, while in DT the genetic material is partially identical as is the case between brothers or sisters. Thus, when a feature is more similar in MT than in DT, this is an argument in favor of a genetic influence. The study was done with 30 pairs of MT and 30 pairs of DT. The number of participants was thus rather large and equally distributed over MT and DT, which is advantageous for the statistical analysis (in the literature, especially, DT are often poorly represented). METHOD Subjects The voices of 30 female MT (ranging in age from 15;6 to 29;7 years;months) and 30 DT (ranging from 15;9 to 29;6 years;months) were analyzed. They were randomly selected from a larger series of twins that participated in a study on the speech characteristics of twins. Some of them were members of the East Flan-
467
ders Prospective Twin Survey and had been invited by the Centre of Human Genetics of Leuven to participate in a longitudinal study on the anthropometric features of twins. However, the greater part were personnally invited or responded to an advertisement in the local weekly paper for students. Addresses were gathered from schools, or from participating twins (the so-called snowball sampling method). The participants selected had no chronic or upper airway problems; they did not smoke intensively nor did they use alcohol on a daily basis; they did not take daily medication; and they did not suffer from heavy vocal load. This information was collected by means of a questionnaire. The twins completed a second questionnaire about the similarity of the twin pair. Based on this information the classification into monozygotic or dizygotic can be made with a certainty of 95%.11 A control group of nonrelated, equally-aged pairs (nonrelated peers, NP) was created in the following way. First, the MT pairs were arranged in order of ascending age. Then this arrangement was maintained for the first members of the pairs, but the second members were exchanged within two successive pairs. Doing so we obtained new voice pairs, with quasi-identical age but without familial relationship. Procedure The subjects read a Dutch standard text (“Papa en Marloes,” 69 words in 8 sentences) at a comfortable loudness and pitch. The voices were recorded on a digital audiotape recorder (DAT, Sony 55ES, Sony Belgium, Brussels, Belgium) connected with a unidirectional microphone (Sennheiser, type MNZ 16T, Sennheiser, Zellik, Belgium); the mouth–microphone distance was 30 cm. Acoustic analysis For acoustic analysis, we used the software MDVP (Multi-Dimensional Voice Program, Kay Elemetrics, Lincoln Park, NJ) model 4305. The signals were captured with a sampling rate of 48.000 and submitted to an F0-analysis for running speech. For each speech sample, the values were calculated from the onset of the first word to the offset of the last word of the text. Two parameters were measured: the mean fundamental frequency (speaking fundamental frequency, “SFF,” in Hz) and the standard deviation of the fundamental frequency (further called “varSFF,” in Hz), during the reading of the text. Journal of Voice, Vol. 16, No. 4, 2002
468
FRANS DEBRUYNE ET AL
Compared with other acoustic variables, the SFF is a stable, robust and well-standardized acoustic measure, less susceptible to procedural and instrumental conditions, and has a relatively low interindividual variability, making it suitable for statistical analysis. The varSFF can be considered as a measure of the vocal pitch variation, which is related by intonation, degree of monotony versus liveliness, and so forth.
TABLE 1. Individual Values of SFF, varSFF and Age in the Monozygotic Twins (MT). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” SFF
varSFF
cotwin1
cotwin2
204
190
80
103
23;06
221
198
107
69
17;05
243
248
105
91
17;03
274
227
99
93
18;05
191
196
64
64
22;01
196
184
68
78
17;10
231
219
135
120
28;04
RESULTS
215
223
85
89
16;00
The individual values of the SFF and the varSF in the different groups (MT, DT, and NP) are seen in Tables 1, 2 and 3. The intrapair correlation coefficients are shown on Table 4. For the SFF there was a highly significant correlation (p < 0.001) in the MT, a weaker correlation (p = 0.036) in the DT and no correlation in the NP (p > 0.05). This means that the similarity of the SFF was most pronounced in MT, less high in DT, and nonexisting in NP. For the varSFF the results were somewhat different. There was no significant intrapair correlation in the NP (p > 0.05) but the correlation was high in the DT as well as in the MT (both p < 0.001). Looking at the individual values, some remarkable results were seen. The dizygotic twin pair no 22, aged 15 years, showed a SFF of 156 Hz and 218 Hz. This means a very low pitch for one twin member, and a rather normal pitch for the other “cotwin.” It corresponded with the subjective pitch impression when listening to the tape. The low voice was maintained during the entire text and did not sound dysphonic. When we omit this result from Table 2, then the correlation coefficient for SFF in DT rises to 0.467 (p = 0.011).
251
235
54
41
23;03
192
193
44
21
15;06
191
212
43
22
21;05
206
180
35
37
23;06
195
200
34
30
19;10
210
193
38
39
22;01
190
204
93
114
19;00
173
179
32
28
21;01
183
181
45
35
20;10
231
209
122
81
29;07
207
194
50
54
19;08
199
199
102
73
23;02
200
187
44
31
22;07
199
192
40
49
22;07
224
215
109
116
22;01
256
243
47
59
21;04
203
214
48
55
21;09
206
203
49
51
21;05
197
199
41
48
21;03
203
204
109
101
18;01
207
223
39
57
17;08
247
220
134
80
28;03
Statistical analysis Individual values of the SFF and varSFF were obtained. To evaluate the intrapair correlation the Pearson’s correlation coefficients (and associated p-values) were calculated for each group (MT, DT, NP), using the software program SPSS (Statistical Package for the Social Sciences, Leuven, Belgium).
cotwin1
cotwin2
age
DISCUSSION Theoretically, the similarity between twin voices found in this study can have three causes. First there can be genetic factors, such as the similar anatomy of the larynx, but also inherited psychological elements Journal of Voice, Vol. 16, No. 4, 2002
which help to determine vocal behaviour. Second, the same environmental factors have influenced the development of the voice since birth. We mention
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS TABLE 2. Individual Values of SFF, varSFF and Age in the Dizygotic Twins (DT). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” SFF
varSFF
cotwin1
cotwin2
cotwin1
cotwin2
age
223
256
154
111
20;01
225
183
80
57
21;09
209
221
95
77
20;05
233
212
94
94
22;01
213
213
90
75
16;03
206
242
92
103
24;00
181
188
66
63
18;04
209
189
107
103
16;04
237
234
101
85
17;11
193
202
46
75
22;02
193
226
75
122
23;01
237
249
108
128
18;11
211
215
61
107
29;06
201
192
45
39
18;05
197
222
42
20
17;07
176
186
23
24
23;08
206
205
95
72
23;06
200
189
26
42
23;01
199
235
49
47
18;11
212
228
36
48
22;06
191
189
52
48
21;00
156
218
44
32
15;09
183
188
51
70
21;06
209
180
46
24
28;00
183
182
33
30
23;02
197
196
35
36
29;03
163
222
39
56
23;05
180
177
33
43
22;02
211
195
90
48
16;01
182
189
46
34
18;06
home and school education, vocal demands, imitation and intratwin mimetism. A third possible factor
469
is the same age of the subjects. In our group (15 to 29 years) a small decrease of SFF with age could be present and lead to a positive intrapair correlation. Thus, a correction for age was necessary. This study clearly shows the stronger similarity of the measured parameters in all twins compared to the results in nontwins. The correlation coefficients were indeed much higher in MT and in DT than in pairs of nonrelated but identically-aged persons. Age is thus not a sufficient explanation. The vocal pitch (SFF and varSFF) of twins is more similar than one could expect on the basis of chance or age. Comparing MT with DT, the results lead to the following conclusions. The SFF was more similar in MT than in DT. This is an argument in favor of a genetic basis. The varSFF, however, was highly correlated in MT ánd in DT. On the basis of this observation it is not possible to separate the share of genetic factors from environmental factors. It is known that the SFF of the voice is dependent on various organic elements such as the length and mass of the vocal folds, while personality and character traits also play a role. For these constituents a genetic basis is supposed to exist. Structural similarity on a genetic basis is reported not only for major anatomic features such as the volume and morphology of larynx and vocal tract,4–6,12 but also for microscopic features such as the ultrastructure of the basal membrane of the vocal fold epithelium.13,14 On the other hand, one could imagine that the varSFF (as a measure of pitch variation and intonation) is highly determined by behavioral and adaptive elements (influenced by environment), thus having an impact on both DT and MT. In this way genetic factors may be overwhelmed and may no longer cause a difference between MT and DT. This explanation may be an oversimplification, but it remains that our results concerning the varSFF do not allow a distinction between genetic and nongenetic causes. In fact, there is always a complex interaction between genotype and environment, as demonstrated by the individual results of the DT where very different SFF’s were found: a very low voice (for a 15-year-old female) versus a normal pitch in her twin sister. It is clear that the individual voice is determined by much more than genetic constitution alone. Journal of Voice, Vol. 16, No. 4, 2002
470
FRANS DEBRUYNE ET AL
TABLE 3. Individual Values of SFF, varSFF and Age in the Nonrelated peers (NP). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” age
SFF
SFF
age
age
varSFF
varSFF
age
15;06
192
223
16;00
15;06
44
89
16;00
16;00
215
193
15;06
16;00
85
21
15;06
17;03
243
198
17;05
17;03
105
69
17;05
17;05
221
248
17;03
17;05
107
91
17;03
17;08
207
184
17;10
17;08
39
78
17;10
17;10
196
223
17;08
17;10
68
57
17;08
18;01
203
227
18;05
18;01
109
93
18;05
18;05
274
204
18;01
18;05
99
101
18;01
19;00
190
194
19;08
19;00
93
54
19;08
19;08
207
204
19;00
19;08
50
114
19;00
19;10
195
181
20;10
19;10
34
35
20;10
20;10
183
200
19;10
20;10
45
30
19;10
21;01
173
199
21;03
21;01
32
48
21;03
21;03
197
179
21;01
21;03
41
28
21;01
21;04
256
212
21;05
21;04
47
22
21;05
21;05
191
243
21;04
21;05
43
59
21;04
21;05
206
214
21;09
21;05
49
55
21;09
21;09
203
203
21;05
21;09
48
51
21;05
22;01
191
193
22;01
22;01
64
39
22;01
22;01
210
196
22;01
22;01
38
64
22;01
22;01
224
187
22;07
22;01
109
31
22;07
22;07
200
215
22;01
22;07
44
116
22;01
22;07
199
199
23;02
22;07
40
73
23;02
23;02
199
192
22;07
23;02
102
49
22;07
23;03
251
190
23;06
23;03
54
103
23;06
23;06
204
235
23;03
23;06
80
41
23;03
23;06
206
220
28;03
23;06
35
80
28;03
28;03
247
180
23;06
28;03
134
37
23;06
28;04
231
209
29;07
28;04
135
81
29;07
29;07
231
219
28;04
29;07
122
120
28;04
Journal of Voice, Vol. 16, No. 4, 2002
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS
471
TABLE 4. Correlation Coefficients r (with p value) for SFF and varSFF in Monozygotic Twins (MT), Dizygotic Twins (DT) and Nonrelated Peers (NP) monozygotic twins n = 30
dizygotic twins n = 30
r
p
r
SFF
0.777
< 0.001
varSFF
0.837
< 0.001
REFERENCES 1. Gedda L, Fiori-Ratti L, Bruno G. La voix chez les jumeaux monozygotiques. Folia Phoniatr. 1960; 12: 81–94. 2. Cornut G. Génèse de la voix de l’enfant. J Fr Otorhinolaryngol-Audiophonol-Chir-Maxillofac. 1971; 20 (2): 411–416. 3. Decoster W, Van Gijsel A, Vercammen J, Debruyne F. Voice similarity in identical twins. Acta Otorhinolaryngol Belg. 2001; 55: 49–55. 4. Luchsinger R. Die erbbiologischen Untersuchungen der Stimme und Sprache. Archiv für die gesamte Phonetik. 1941; 5: 41–45. 5. Schilling R. Uber die Stimme erbgleicher Zwillinge. Folia Phoniatr. 1950; 2: 98–112. 6. Flach M, Schwickardt H, Steinert R. Zur Frage des Einflusses erblicher Faktoren auf den Stimmklang (Zwillingsuntersuchungen). Folia Phoniatr. 1968; 20: 369–378. 7. Przybyla B, Horii Y, Crawford M. Vocal fundamental frequency in a twin sample: looking for a genetic effect. J Voice. 1992; 6: 261–266.
non-related peers n = 30
p
r
p
0.385
0.036
-0.084
> 0.05
0.761
< 0.001
0.114
> 0.05
8. Fuchs M, Oeken J, Hotopp T; Taschner R, Hentschel B, Behrendt W. Die Ahnlichkeit monozygoter Zwillinge hinsichtlich Stimmleistungen und akustischer Merkmale und ihre mogliche klinische Bedeutung. HNO. 2000; 48: 462– 469. 9. Forrai G, Gordos G. A new acoustic method for the discrimination of monozygotic and dizygotic twins. Acta Paediatrica Hungarica. 1983; 24: 315–321. 10. Ostwald PF, Freedman DG, Kurtz. Vocalization of infant twins. Folia Phoniatr. 1962; 14:37–50. 11. Peeters H, Van Gestel S, Vlietinck R, Derom C, Derom R. Validation of a telephone zygosity questionnaire in twins of known zygosity. Behav Genet. 1998; 28: 159–163. 12. Sataloff RT. Genetics of the voice. J Voice. 1995; 9: 16–19. 13. Gray S, Pignatari S, Harding P. Morphologic ultrastructure of anchoring fibers in normal fold basement membrane zone. J Voice. 1994; 8: 48–52. 14. Rubin JS, Sataloff RT. Voice new horizons. In: Sataloff RT. Professional Voice. The Science and Art of Clinical Care. 2nd ed. San Diego, Calif: Singular Publishing Group; 1997: 801–808.
Journal of Voice, Vol. 16, No. 4, 2002
Speaking Fundamental Frequency in Monozygotic and Dizygotic Twins Frans Debruyne, Wivine Decoster, Annemie Van Gijsel, and Julie Vercammen Experimental Otorhinolaryngology, University of Leuven, Belgium
Summary: The speaking fundamental frequency (SFF) and the intraindividual variation of the SFF during the reading of a Dutch standard text were measured in 30 female monozygotic twins (MT) and 30 dizygotic twins (DT), aged 15–29 years. A control group was created that consisted of 30 nonrelated paired individuals of equal age. Studying the intrapair correlation coefficients it seemed that the SFF was similar to a greater degree in MT and to a lesser degree in DT, while there was no correlation at all in nonrelated peers. These results are compatible with a genetic basis for the SFF. On the other hand, the intraindividual variation of the SFF was highly similar in MT and in DT (but not in nonrelated peers), so that for this parameter it was not possible to discern the influences of genetic disposition and shared environment. Key Words: Twin voice—Speaking fundamental frequency.
not genetically related to the twin; they obtained a correct identification of 82%, which is significantly more than by chance (33%). Besides these perceptive studies, investigators have measured and compared various acoustic characteristics of twin voices. One of the first parameters reported in this context was the vocal range in semitones, which was found to be very similar, especially in monozygotic twins.4,5 Flach6 measured the vocal range in 10 monozygotic twins and reported an identical range in eight pairs and a difference of one semitone in two pairs. Later, various objective acoustic measures in the frequency and time domain were studied. Similarities of the speaking fundamental frequency (SFF) in MT have been reported by Schilling,5 Gedda1 and Cornut.2 Przybyla7 examined the SFF of monozygotic and dizygotic twins and found an intrapair correlation coefficient of 0.539 for monozygotic twins and 0.338 for dizygotic twins, after correction for age and weight. More recently, Fuchs8 performed a statistical
INTRODUCTION Because twins resemble each other in many aspects, one expects that their voices also may sound similar at least to a certain degree. This expectation seems verified in daily life, when it can be hard to determine which member of a twin is speaking on the telephone. Studies with listeners have confirmed this perceptive similarity. It has been observed that twins themselves have difficulties identifying their own voices when presented recordings, in random order, of their own voice and the voice of their twin.1,2 Decoster et al 3 asked listeners to identify twin voices within voice trios. Each of these trios was randomly assembled by the two voices of a female twin and a third voice of another, age-matched woman who was Accepted for publication June 11, 2002 Address correspondence and reprint requests to Prof. F. Debruyne, Otorhinolaryngology—Head and Neck Surgery, U.Z. St. Rafaël, Kapucijnenvoer 33, 3000 Leuven, Belgium e-mail: [email protected]
466
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS study in a larger group of subjects (31 monozygotic twins) and found that the SFF is an acoustic feature which is significantly more similar in monozygotic twins than in nonrelated persons. Furthermore, various studies also concerned resonance-related characteristics. It was found that the number of harmonics and the general form of the frequency spectrum may be more similar in monozygotic twins compared with dizygotic twins1,6 or with pairs of nonrelated persons.8 Also Forrai and Gordos9 reported a positive correlation between similarity of spectral characteristics and monozygosy versus dizygosy. In contrast, Ostwald10 found no significant similarity when examining spectograms of the infant cry of 16 twin pairs (during the first month of life). In our investigation we studied two characteristics of the vocal fundamental frequency: the average fundamental frequency (speaking fundamental frequency, or “SFF”) and the intraindividual variation of the fundamental frequency (“varSFF”), both during the reading of a standard text. The aim of the investigation was (1) to study if twin voices are similar to each other concerning this parameters (if positive, one can speculate that these parameters could contribute to the fact that listeners perceive twin voices as similar), and (2) to study to what extent the observed similarity is genetically determined, by comparing the results in monozygotic twins (MT) with the results in dizygotic twins (DT). MT have a completely identical genotype, while in DT the genetic material is partially identical as is the case between brothers or sisters. Thus, when a feature is more similar in MT than in DT, this is an argument in favor of a genetic influence. The study was done with 30 pairs of MT and 30 pairs of DT. The number of participants was thus rather large and equally distributed over MT and DT, which is advantageous for the statistical analysis (in the literature, especially, DT are often poorly represented). METHOD Subjects The voices of 30 female MT (ranging in age from 15;6 to 29;7 years;months) and 30 DT (ranging from 15;9 to 29;6 years;months) were analyzed. They were randomly selected from a larger series of twins that participated in a study on the speech characteristics of twins. Some of them were members of the East Flan-
467
ders Prospective Twin Survey and had been invited by the Centre of Human Genetics of Leuven to participate in a longitudinal study on the anthropometric features of twins. However, the greater part were personnally invited or responded to an advertisement in the local weekly paper for students. Addresses were gathered from schools, or from participating twins (the so-called snowball sampling method). The participants selected had no chronic or upper airway problems; they did not smoke intensively nor did they use alcohol on a daily basis; they did not take daily medication; and they did not suffer from heavy vocal load. This information was collected by means of a questionnaire. The twins completed a second questionnaire about the similarity of the twin pair. Based on this information the classification into monozygotic or dizygotic can be made with a certainty of 95%.11 A control group of nonrelated, equally-aged pairs (nonrelated peers, NP) was created in the following way. First, the MT pairs were arranged in order of ascending age. Then this arrangement was maintained for the first members of the pairs, but the second members were exchanged within two successive pairs. Doing so we obtained new voice pairs, with quasi-identical age but without familial relationship. Procedure The subjects read a Dutch standard text (“Papa en Marloes,” 69 words in 8 sentences) at a comfortable loudness and pitch. The voices were recorded on a digital audiotape recorder (DAT, Sony 55ES, Sony Belgium, Brussels, Belgium) connected with a unidirectional microphone (Sennheiser, type MNZ 16T, Sennheiser, Zellik, Belgium); the mouth–microphone distance was 30 cm. Acoustic analysis For acoustic analysis, we used the software MDVP (Multi-Dimensional Voice Program, Kay Elemetrics, Lincoln Park, NJ) model 4305. The signals were captured with a sampling rate of 48.000 and submitted to an F0-analysis for running speech. For each speech sample, the values were calculated from the onset of the first word to the offset of the last word of the text. Two parameters were measured: the mean fundamental frequency (speaking fundamental frequency, “SFF,” in Hz) and the standard deviation of the fundamental frequency (further called “varSFF,” in Hz), during the reading of the text. Journal of Voice, Vol. 16, No. 4, 2002
468
FRANS DEBRUYNE ET AL
Compared with other acoustic variables, the SFF is a stable, robust and well-standardized acoustic measure, less susceptible to procedural and instrumental conditions, and has a relatively low interindividual variability, making it suitable for statistical analysis. The varSFF can be considered as a measure of the vocal pitch variation, which is related by intonation, degree of monotony versus liveliness, and so forth.
TABLE 1. Individual Values of SFF, varSFF and Age in the Monozygotic Twins (MT). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” SFF
varSFF
cotwin1
cotwin2
204
190
80
103
23;06
221
198
107
69
17;05
243
248
105
91
17;03
274
227
99
93
18;05
191
196
64
64
22;01
196
184
68
78
17;10
231
219
135
120
28;04
RESULTS
215
223
85
89
16;00
The individual values of the SFF and the varSF in the different groups (MT, DT, and NP) are seen in Tables 1, 2 and 3. The intrapair correlation coefficients are shown on Table 4. For the SFF there was a highly significant correlation (p < 0.001) in the MT, a weaker correlation (p = 0.036) in the DT and no correlation in the NP (p > 0.05). This means that the similarity of the SFF was most pronounced in MT, less high in DT, and nonexisting in NP. For the varSFF the results were somewhat different. There was no significant intrapair correlation in the NP (p > 0.05) but the correlation was high in the DT as well as in the MT (both p < 0.001). Looking at the individual values, some remarkable results were seen. The dizygotic twin pair no 22, aged 15 years, showed a SFF of 156 Hz and 218 Hz. This means a very low pitch for one twin member, and a rather normal pitch for the other “cotwin.” It corresponded with the subjective pitch impression when listening to the tape. The low voice was maintained during the entire text and did not sound dysphonic. When we omit this result from Table 2, then the correlation coefficient for SFF in DT rises to 0.467 (p = 0.011).
251
235
54
41
23;03
192
193
44
21
15;06
191
212
43
22
21;05
206
180
35
37
23;06
195
200
34
30
19;10
210
193
38
39
22;01
190
204
93
114
19;00
173
179
32
28
21;01
183
181
45
35
20;10
231
209
122
81
29;07
207
194
50
54
19;08
199
199
102
73
23;02
200
187
44
31
22;07
199
192
40
49
22;07
224
215
109
116
22;01
256
243
47
59
21;04
203
214
48
55
21;09
206
203
49
51
21;05
197
199
41
48
21;03
203
204
109
101
18;01
207
223
39
57
17;08
247
220
134
80
28;03
Statistical analysis Individual values of the SFF and varSFF were obtained. To evaluate the intrapair correlation the Pearson’s correlation coefficients (and associated p-values) were calculated for each group (MT, DT, NP), using the software program SPSS (Statistical Package for the Social Sciences, Leuven, Belgium).
cotwin1
cotwin2
age
DISCUSSION Theoretically, the similarity between twin voices found in this study can have three causes. First there can be genetic factors, such as the similar anatomy of the larynx, but also inherited psychological elements Journal of Voice, Vol. 16, No. 4, 2002
which help to determine vocal behaviour. Second, the same environmental factors have influenced the development of the voice since birth. We mention
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS TABLE 2. Individual Values of SFF, varSFF and Age in the Dizygotic Twins (DT). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” SFF
varSFF
cotwin1
cotwin2
cotwin1
cotwin2
age
223
256
154
111
20;01
225
183
80
57
21;09
209
221
95
77
20;05
233
212
94
94
22;01
213
213
90
75
16;03
206
242
92
103
24;00
181
188
66
63
18;04
209
189
107
103
16;04
237
234
101
85
17;11
193
202
46
75
22;02
193
226
75
122
23;01
237
249
108
128
18;11
211
215
61
107
29;06
201
192
45
39
18;05
197
222
42
20
17;07
176
186
23
24
23;08
206
205
95
72
23;06
200
189
26
42
23;01
199
235
49
47
18;11
212
228
36
48
22;06
191
189
52
48
21;00
156
218
44
32
15;09
183
188
51
70
21;06
209
180
46
24
28;00
183
182
33
30
23;02
197
196
35
36
29;03
163
222
39
56
23;05
180
177
33
43
22;02
211
195
90
48
16;01
182
189
46
34
18;06
home and school education, vocal demands, imitation and intratwin mimetism. A third possible factor
469
is the same age of the subjects. In our group (15 to 29 years) a small decrease of SFF with age could be present and lead to a positive intrapair correlation. Thus, a correction for age was necessary. This study clearly shows the stronger similarity of the measured parameters in all twins compared to the results in nontwins. The correlation coefficients were indeed much higher in MT and in DT than in pairs of nonrelated but identically-aged persons. Age is thus not a sufficient explanation. The vocal pitch (SFF and varSFF) of twins is more similar than one could expect on the basis of chance or age. Comparing MT with DT, the results lead to the following conclusions. The SFF was more similar in MT than in DT. This is an argument in favor of a genetic basis. The varSFF, however, was highly correlated in MT ánd in DT. On the basis of this observation it is not possible to separate the share of genetic factors from environmental factors. It is known that the SFF of the voice is dependent on various organic elements such as the length and mass of the vocal folds, while personality and character traits also play a role. For these constituents a genetic basis is supposed to exist. Structural similarity on a genetic basis is reported not only for major anatomic features such as the volume and morphology of larynx and vocal tract,4–6,12 but also for microscopic features such as the ultrastructure of the basal membrane of the vocal fold epithelium.13,14 On the other hand, one could imagine that the varSFF (as a measure of pitch variation and intonation) is highly determined by behavioral and adaptive elements (influenced by environment), thus having an impact on both DT and MT. In this way genetic factors may be overwhelmed and may no longer cause a difference between MT and DT. This explanation may be an oversimplification, but it remains that our results concerning the varSFF do not allow a distinction between genetic and nongenetic causes. In fact, there is always a complex interaction between genotype and environment, as demonstrated by the individual results of the DT where very different SFF’s were found: a very low voice (for a 15-year-old female) versus a normal pitch in her twin sister. It is clear that the individual voice is determined by much more than genetic constitution alone. Journal of Voice, Vol. 16, No. 4, 2002
470
FRANS DEBRUYNE ET AL
TABLE 3. Individual Values of SFF, varSFF and Age in the Nonrelated peers (NP). The SFF and varSFF are expressed in Hz (three decimal places being used in the statistical calculations but omitted in the table for purpose of clarity). Age in “years;months.” age
SFF
SFF
age
age
varSFF
varSFF
age
15;06
192
223
16;00
15;06
44
89
16;00
16;00
215
193
15;06
16;00
85
21
15;06
17;03
243
198
17;05
17;03
105
69
17;05
17;05
221
248
17;03
17;05
107
91
17;03
17;08
207
184
17;10
17;08
39
78
17;10
17;10
196
223
17;08
17;10
68
57
17;08
18;01
203
227
18;05
18;01
109
93
18;05
18;05
274
204
18;01
18;05
99
101
18;01
19;00
190
194
19;08
19;00
93
54
19;08
19;08
207
204
19;00
19;08
50
114
19;00
19;10
195
181
20;10
19;10
34
35
20;10
20;10
183
200
19;10
20;10
45
30
19;10
21;01
173
199
21;03
21;01
32
48
21;03
21;03
197
179
21;01
21;03
41
28
21;01
21;04
256
212
21;05
21;04
47
22
21;05
21;05
191
243
21;04
21;05
43
59
21;04
21;05
206
214
21;09
21;05
49
55
21;09
21;09
203
203
21;05
21;09
48
51
21;05
22;01
191
193
22;01
22;01
64
39
22;01
22;01
210
196
22;01
22;01
38
64
22;01
22;01
224
187
22;07
22;01
109
31
22;07
22;07
200
215
22;01
22;07
44
116
22;01
22;07
199
199
23;02
22;07
40
73
23;02
23;02
199
192
22;07
23;02
102
49
22;07
23;03
251
190
23;06
23;03
54
103
23;06
23;06
204
235
23;03
23;06
80
41
23;03
23;06
206
220
28;03
23;06
35
80
28;03
28;03
247
180
23;06
28;03
134
37
23;06
28;04
231
209
29;07
28;04
135
81
29;07
29;07
231
219
28;04
29;07
122
120
28;04
Journal of Voice, Vol. 16, No. 4, 2002
SPEAKING FUNDAMENTAL FREQUENCY IN TWINS
471
TABLE 4. Correlation Coefficients r (with p value) for SFF and varSFF in Monozygotic Twins (MT), Dizygotic Twins (DT) and Nonrelated Peers (NP) monozygotic twins n = 30
dizygotic twins n = 30
r
p
r
SFF
0.777
< 0.001
varSFF
0.837
< 0.001
REFERENCES 1. Gedda L, Fiori-Ratti L, Bruno G. La voix chez les jumeaux monozygotiques. Folia Phoniatr. 1960; 12: 81–94. 2. Cornut G. Génèse de la voix de l’enfant. J Fr Otorhinolaryngol-Audiophonol-Chir-Maxillofac. 1971; 20 (2): 411–416. 3. Decoster W, Van Gijsel A, Vercammen J, Debruyne F. Voice similarity in identical twins. Acta Otorhinolaryngol Belg. 2001; 55: 49–55. 4. Luchsinger R. Die erbbiologischen Untersuchungen der Stimme und Sprache. Archiv für die gesamte Phonetik. 1941; 5: 41–45. 5. Schilling R. Uber die Stimme erbgleicher Zwillinge. Folia Phoniatr. 1950; 2: 98–112. 6. Flach M, Schwickardt H, Steinert R. Zur Frage des Einflusses erblicher Faktoren auf den Stimmklang (Zwillingsuntersuchungen). Folia Phoniatr. 1968; 20: 369–378. 7. Przybyla B, Horii Y, Crawford M. Vocal fundamental frequency in a twin sample: looking for a genetic effect. J Voice. 1992; 6: 261–266.
non-related peers n = 30
p
r
p
0.385
0.036
-0.084
> 0.05
0.761
< 0.001
0.114
> 0.05
8. Fuchs M, Oeken J, Hotopp T; Taschner R, Hentschel B, Behrendt W. Die Ahnlichkeit monozygoter Zwillinge hinsichtlich Stimmleistungen und akustischer Merkmale und ihre mogliche klinische Bedeutung. HNO. 2000; 48: 462– 469. 9. Forrai G, Gordos G. A new acoustic method for the discrimination of monozygotic and dizygotic twins. Acta Paediatrica Hungarica. 1983; 24: 315–321. 10. Ostwald PF, Freedman DG, Kurtz. Vocalization of infant twins. Folia Phoniatr. 1962; 14:37–50. 11. Peeters H, Van Gestel S, Vlietinck R, Derom C, Derom R. Validation of a telephone zygosity questionnaire in twins of known zygosity. Behav Genet. 1998; 28: 159–163. 12. Sataloff RT. Genetics of the voice. J Voice. 1995; 9: 16–19. 13. Gray S, Pignatari S, Harding P. Morphologic ultrastructure of anchoring fibers in normal fold basement membrane zone. J Voice. 1994; 8: 48–52. 14. Rubin JS, Sataloff RT. Voice new horizons. In: Sataloff RT. Professional Voice. The Science and Art of Clinical Care. 2nd ed. San Diego, Calif: Singular Publishing Group; 1997: 801–808.
Journal of Voice, Vol. 16, No. 4, 2002