Vocalization of Infant Twins

Abstract

Sixteen pairs of infant twins were tape-recorded during the first month of life. Their spontaneous full cries upon awakening were studied by means of an H. H. Scott half-octave-band Sound Analyzer. Analysis of musical patterns and comparison of the phonetic characteristics of the cries were also done. With these methods it was possible to demonstrate similarities in the cries of certain twin pairs and differences in those of others, and this was also confirmed in two pairs analyzed spectrographically. However, the statistical correlation of intra-pair similarity with monozygosity and of intrapair difference with dizygosity was no greater than chance. Consideration must therefore be given to factors other than heredity which determine similarities and differences between the cries of twin-partners during the first month of life. These include variability in the spontaneous crying patterns of the individual babies, and intrapair discrepancies in physical maturation and strength. It is still an open question whether vocal behavior can be directly related to genetic influence, and we plan to continue to study this matter.