Speech/language studies with twins

Allen, G., Harvald, B., and Shields, J. (1967) Measures of twin concordance. Acta Genetica Med. Gemellol. 17 , 475-81

A methodological note concerning the calculation of concordance rates for heritable traits or succeptability to disease, comparing pairwise concordance (c/c+d, where c=# of concordant pairs, c=#of discordant pairs) with proband concordance rate (c+x/c+x+d, where x = number of independently ascertained pairs). The point is that in a study of twins meant to generalize to the non-twin population the twins are (usually) not a random sample from the population - they come in pairs.

Alpert, M., Kurtzberg, R.L., Pilot, M. & Friedhoff, A.J. (1963) Spectral characteristics of the voices of twins. Acta Genetica Med. Gemellol. 12 , 335-341.

Studied relative spectral amplitudes, averaged over pronunciations of the letters 'a', 'e', 'i', 'o', 'u', produced by six MZ pairs (3 male, 3 female) and six DZ pairs (4 male, 2 female). Ages ranged from 16 to 50 years. MZ twins were no less different from each other than were DZ twins for frequencies below 500 Hz, but the twins were less different from each other than were un-related (but age and sex matched) pairs of speakers [data below 500 Hz appears to be somewhat unreliable]. MZ twins were more alike than were DZ twins at frequencies above 500 Hz, and the DZ twins differed by as much as the difference between unrelated pairs in 3 of the 4 frequency bands above 500 Hz which were measured. "The results support the primary hypothesis that the voices of MZ twins are more similar than DZ twins at higher spectral points" (p. 339).

Cescato, M. S., & Mertin, P. G. (1986). Cognitive functioning of children born with very low birth weight. In Pratt, C., Gartow, A. F., Turmer, W. E., Nesdale, A. R., (Eds.), Research issues in child development . Allen & Unwin.

Conway, D., Lytton, H., & Pysh, F. (1980). Twin-singleton language differences. Canad. J. Behav. Sci 12 , 264-271.

Davis, E. A. (1937). The development of linguistic skill in twins, sinlgetons, and sibs, and only children from 5-10. University of Minnesota Institute of Child Welfare, Monograph 14.

Day, E. J. (1932) The development of language in twins. 1. A comparison of twins and single children. 2. The development of twins: their resemblances and differences. Child Development 3 , 179-199, 298-316.

Dodd, Barbera and McEvoy, Sandra (1994) Twin language or phonological disorder? Journal of Child Language 21 , 273-89.

An investigation of 'twin language'. 19 sets of 2-4 year old twins/triplets. Results indicate the presence of phonological disorders in these children, but differences in the particular pronunciation patterns of twins. Twins could understand each other's 'error forms' better than could unrelated children (57% correct vs. 38% correct). Dodd & McEvoy suggest that 'MBC's [multiple-birth children'] lexicons sometimes store two phonological forms for word recognition' (p. 287). However, there was no evidence for an autonomous language among these twins.

Figueiredo, Ricardo Molina de (1993) The Effectiveness of Long-Term Spectral Measurements for the Identification of Speakers; A eficacia de medidas extraidas do espectro de longo termo para a identificacao de Falantes. Cadernos-de-Estudos-Linguisticos 25 : 129-160.

Long-term spectra (LTS) were extraced from normal & rapid text-reading performances of healthy male informants (N = 10), including one set of twins. Each LTS is expressed as amplitude at 200 points defined by 40-hertz (Hz) steps along the frequency axis from 40 to 8,000 Hz. Cluster analyses are based on point measurements, selected frequency bands, & a combination of slopes, residues, & average band amplitude. Effects of emission rate on LTS & amplitude ratio between LTS bands are studied. Results confirm that LTS is an effective indictor of speaker identity. The point-based cluster analysis successfully identified the twins despite very similar LTS. Analysis based on slopes & residues, ie, on more global measurements, did not vitiate speaker identification.

Gedda, L., Bianchi, A. and Bianchi-Neroni, L. (1955) La voce dei gemelli, I. Prova di identificazionne intrageminale della voce in 104 coppie (58 MZ e 46 DZ). Acta geneticae Medicae et Gemellologiae 4 , 121-130.

A study of the relative similarity of the voices of monozygotic and dizygotic twins voices. As indicated in the title, 104 pairs were studied; their ages ranged from 8 to 16 years. Recordings (evidently of a relatively long passage) were made and then a twin heard his/her own recording and that of his/her twin. For 66% of the monozygotic twins neither member of the pair could tell his/her own voice from the twin's. Only 2% of the dizygotic twins found their own voices this confusing. For 78% of the dizygotic pairs both could discriminate his/her own voice from the twin's; only 13% of the monozygotic pairs accomplished this. One wishes that Gedda, et al. had broken the data down into age groups because it would be interesting to know if the 13% of MZ twins who could perform the discrimination tended to be older or younger than the MZ twins who couldn't.

Gedda, L., Fiori-Ratti, L. and Bruno, G. (1960) La voix chez les jumeauz monozygotiques. Folia Phoniatrica 12 , 81-94.

A follow-up on the 1955 study, this paper reports some acoustic measurements of speech produced by MZ (20 pairs) and DZ (4 pairs) twins. Apparently, crude long-term average spectra were taken and difference LTA spectra calculated for each pair. MZ twins showed remarkably similar spectra while DZ twins showed greater divergence. 'Fundamental frequency' in MZ twins was also compared (though even with these prepubescent twins the reported values are implausibly high [300-800 Hz]). The values for the MZ twins were very similar, while variation across twin pairs was quite broad.

Howie, Pauline M. (1981) Concordance for stuttering in monozygotic and dizygotic twins. Journal of Speech and Hearing Research , 24 , 317-321.

Lewis, Barbara A. & Thompson, Lee A. (1992) A study of developmental speech and language disorders in twins. J. of Speech and Hearing Res. 35 , 1086-1094.

32 MZ and 25 DZ twins were examined for concordance of speech and language disorders. Data were classifications of speech or language disorder determined from an interview with the parents, and scores on standardized vocabulary, spelling and reading tests. Mean age of twins 9.35 years. Male/female ratio 2.8/1 is somewhat higher than the commonly reported sex ratio for speech/language disorders (2.4/1.5). No significant differences between MZ and DZ twins on socio-economic class, sex, or age. Of the 32 MZ pairs, in 24 both twins had a speech/language disorder, of the 25 DZ pairs only 8 did. Probandwise concordance rates were MZ 0.86, DZ 0.48. In terms of concordance for the broad type of disorder:


	MZ	DZ
articulation	0.95	0.22
learning disorder	0.53	0.33


This study must be taken with a grain of salt because the data are not direct observation but filtered through parental descriptions of the children's behavior.

Locke, John L. and Mather, Patricia, L. (1989) Genetic factors in the ontogeny of spoken language: Evidence from monozygotic and dizygotic twins. Journal of Child Language 16 , 553-9.

Reanalysis of the Mather and Black data. 13 MZ and 13 DZ pairs, 85% correct or less on the Templin-Darley articulation test, matched for age and sex. MZ scored 55% correct while DZ pairs scored 71% (high end of range was the same, but MZ showed more variation). 82% concordance of errors for MZ (same items on T-D missed by both MZ twins), 56% concordance for DZ (which matches the concordance rate for age-sex matched unrelated pairs). Weakness of the study is that missing the same item on the T-D test does not mean that the mispronunciations matched, and in another analysis Locke and Mather concluded "MZ twins were not necessarily more likely than DZ twins to produce error sounds in precisely the same way" (p. 558). One wonders if the concordance is for vocabulary items rather than speech patterns.

Luchsinger, R. (1959) Die Vererbung von Sprach- und Stimmstörungen. Folia Phoniatrica 11 , 7-64.

Luchsinger, R. (1961) Die Sprachentwicklung von ein- und zweieiigen Zwillingen und die Vererbung von Sprachstörungen in den ersten drei Lebensjahren. Folia Phoniatrica 13 , 66-76.

Lundstrom, Anders (1948) Tooth Size and Occlusion in Twins. Basle: S. Karger.

Extensive and very careful measurements of mouth dimensions in 202 pairs of twins (100 monozygotic, 102 dizigotic). Results are given in standard deviations of intrageminal (twin) differences. Here is a table of the main findings:

	identical	fraternal
Upper Tooth size (I1 + I 2 + C ... M1, in mm)	1.28	4.69
Lower Tooth size	1.11	4.17
Upper Arch space (length from M1 to M1, in mm)	2.25	5.62
Lower Arch space	1.28	3.45
Upper Width of dental arch (in mm)	1.77	2.63
Lower Width of dental arch	1.32	2.7
Upper Length of dental arch (in mm)	1.28	2.99
Lower Length of dental arch (in mm)	1.01	2.04
Inclination of upper incisors (in degrees)	1.96	5.17
Height of the palatal vault (in mm)	1.03	1.96
Sagital overbite (in mm)	1.37	2.87

"The factors governing the variation in identical pairs of twins are of a similar kind as those causing differences between the halves of the body i.e. the factors which at an early stage become effective, probably in the embryonic stage only" (p. 102-3).

Luria, A. R. & Yudovitch, F. I. (1959). Speech and the Development of Mental Processes in the Child. London: Staples Press.

Lytton, H. (1980). Parent-child interaction. The socialization process observed in twin and singleton families . Plenum, New York.

Lytton, H., Conway, D., & Sauve, R., (1977). The impact of twinship on parent-child interaction. Journal of Personality and Social Psychology 25 , 97-107.

Malmstrom, P. M., & Silva, M. N. (1986). Twin talk: manifestations of twins status in the speech of toddlers. Journal of Child Language 13 , 293-304.

Matheny, A. P., Jr., & Bruggemann, C.E. (1972). Articulation proficiency in twins and singletons from families of twins. Journal of Speech and Hearing Research 15 , 845-851.

Matheny, A. P., Jr., & Bruggemann, C.E. (1973) Children's speech: Hereditary components and sex differences. Folia Phoniatrica , 25 , 442-9.

Mather, Patricia L. & Black, Kathryn N. (1984) Hereditary and environmental influences on preschool twin's language skills. Developmental Psychology 20 , 303-8.

50 MZ and 29 DZ (average age 4.5 years) were tested. A variety of psycholinguistic tests (expressive, receptive, and grammatical aspects of language use) were administered. Only one of seven tests showed an significant heritable component. This was the Peabody Picture Vocabulary Test, a measure of receptive vocabulary or language comprehension, all other tests assessed language performance skills. Intraclass correlations for the PPVT were .78 for MZ twins and .44 for DZ twins.

McCarthy, D. (1954). Language development in children. In L. Carmichael (Ed.), Manual of Child Psychology (pp. 492-630). New York: Wiley.

Mittler, P. (1970). Biological and social aspects of language development in twins. Develop. Med. Child Neurol. , 12 741-757.

Mogford, K. (1993). Language development in twins. In D. Bishop & K. Mogford (Eds.), Language development in exceptional circumstances (pp. 80-95). Hove, UK: Lawrence Erlbaum.

Mohay, H., Burns, Y., & Luke, D. (1986). The effects of prenatal and postnatal twin environments on development. In Pratt, C., Gartow, A. F., Turmer, W. E., Nesdale, A. R., Research issues in child development . Allen & Unwin.

Nichols, R.C. and Bilbro, W.C. Jr. (1966) The diagnosis of twin zygosity. Acta Genetica Med. Gemellol 16 , 265-275.

This article describes a technique for determining zygosity from answers to a brief questionaire. Based on data from 123 pairs of twins for whom zygosity was determined by blood tests, an algorithm for evaluating questionaire responses was developed. Accuracy of 93% correct was obtained, and in a test of the method on a group of 1239 sets of twins 95% could be unambiguously classified.

Nolan, Francis; Oh, Tomasina (1996) Identical Twins, Different Voices. Forensic Linguistics 3 : 39-49.

Differences in articulation of the phonemes /r/ & /l/ by identical twins (N = 3 pairs, aged 20-23) were acoustically examined. Coarticulation of initial /r/ & /l/ followed by 10 vowel phonemes were analyzed using recordings of Ss reading 60 words divided into 4 lists. Frequencies were measured for the first four formants of each beginning consonant & vowel, where possible. Coarticulation within all three sets of twins were found to be similar; however, two of the pairs showed consistent frequency differences in one or two formants, & the other pair also realized alternative pronunciations. Articulatory configurations explaining the differences are described; auditory salience of the phoneme choices varied. Further study should shed light on speaker identification in cases involving identical twins, taking into account their freedom to choose among variants sanctioned by a speech community.

Osborne, R. Travis, Gregor, A. James, and Miele, Frank (1968) Heritability of factor V: Verbal comprehension. Perceptual and Motor Skills 26 , 191-202.

Ostwald, P.F., Freedman, D.G., and Kurtz, J.H. (1962) Vocalization of infant twins. Folia Phoniatrica 14 , 37-50.

Plomin, Robert and Daniels, Denise (1987) Why are children in the same family so different from one another? Behavioral and Brain Sciences , 10 , 1-60.

Survey of a large number of behavioral-genetic research focusing on the role of non-shared environment in cognitive and behavioral characteristics.

Record, R. G., McKeown, T., & Edwards, J. H. (1970). An investigation of the difference in measured intelligence between twins and single births. Annals of Human Genetics 34 , 11-20.

Reznick, J. S. (1997). Intelligence, language, nature, and nurture in young twins. In R. J. Sternberg & E. L. Grigorenko (Eds.) Inteligence, Heredity, and Environement . Cambridge University Press.

Examination of 408 twin pairs (210 Mz, 177 DZ, 21 ?, 90% caucasian) at 14, 20, 24 months. Standardized tests (BSID, SICD) were administered in the home. Interestingly, parent report items on these measures indicated higher correlations among twins than did the observer-reported measures indicating perhaps that parents conflate the twins' performance. Word comprehension tests were also administered in the laboratory using a head turning task. Correlations between this task and the receptive language sections of the standardized tests ranged from r=.19 to .37, nonetheless they were pooled into a composite receptive language score. Some findings: stepwise regression predicting the MDI (mental development index) found that expressive measures were better correlated in contemporaneous models while receptive measures were better predictors of subsequent MDI scores. A methodological interpretation, the MDI contains more items that reflect expressive language, however the relationship between MDI and previous receptive scores does not appear to be an artifact. Comparing MZ and DZ twins finds stong evidence for environmental effects on both expressive and receptive language abilities, but a significant index of heritability only in expressive language and only then at 24 months. As pointed out this may reflect mediation through temperament (shyness in the context of speaking to a stranger).

Reznick, J. S., Corley, R., & Robinson, J. (In press). A longitudinal twin study of intelligence in the second year. Monographs of the Society for Research in Child Development.

Savic, S. (1979). Mother-child verbal interaction: The functioning of completions in the twin situation. Journal of Child Language 6 , 153-158.

Savic, S. (1980). How twins learn to talk . New York: Academic Press.

Schilling, R. (1950) Über die Stimme erbgleicher Zwillinge. Folia Phoniatrica 2 , 98-119.

Segal, Nancy L. (1985) Monozygotic and dizygotic twins: A comparative analysis of mental ability profiles. Child Development 56 , 1051

Shopen, Glenda and Shopen, Tim (1995) Something "very" happens: Language acquisition in early childhood. Australian Journal of Early Childhood 20, 28-32.

Superficial case study of language development in one pair of twins. Some examples of shared non-standard usages such as the very of the title.

Stafford, L. (1987). Maternal input to twin and singleton children: Implications for langage acquisition. Human Communication Research 13 , 429-462.

Suzuki, Takao; Nomura, Hiroshi (1983) A Study of Pitch on Twins' Voice (Japanese) Bulletin, The Phonetic Society of Japan 172 : 4-6.

Five Japanese vowels uttered by 13 M & 18 F pairs of identical twins, 16-17 years) were analyzed by FFT technique. As the result of pitch analysis, 99% of M & F twins had similar pitches; 98% of M twins & 81% of F twins had similar pitch variation ratio in 5-vowel utterances. Pitch variation ratio means that a pitch changes ratio between a pitch of one vowel utterance & a pitch of the next vowel utterance.

Tomasello, M., Mannle, S. & Kruger, A. (1986). Linguistic environment of 1- to 2-year-old twins. Developmental Psychology 22 , 169-176.

Vandenberg, Steven G., McKusick, Victor A., and McKusick, Anne B. (1962) Twin data in support of the Lyon Hypothesis. Nature 194 , 505-6.

Vandenberg, Steven G. (1962) The hereditary abilities study: Hereditary components in a psychological test battery. American Journal of Human Genetics 14 , 220-37.

Wing, Clara S. (1990) Defective infant formulas and expressive language problems: A case study. Language, Speech, and Hearing Services in the Schools 21 , 22-27.

A case study verifying the adverse effects of chloride deficient infant formula. One twin was given the defective formula (before it was taken off the market) and the other was not. The affected twin showed much delayed language acquisition and language impairment persisted to time of testing at 8.5 yrs. No effects on non-verbal reasoning, receptive vocabulary, but marked differences between the two in word retrieval/verbal response tasks.

Winnen, Lotte and Winnen, Willy (1958) Über einen Fall von Vokalsprache bei eineiigen Zwillingen. Folia Phoniatrica 10 , 182-189.

A case of 'twin language' in a pair of five year old twin boys is the subject of this report. The children are reported to employ only the vowel sounds of nouns. For example, e a ei to = <es hat einen Kopf>

Zazzo, R. (1960). Les jumeaux: Le couple et la personne . Paris: P.U.F.