The Authors describe the methodology of an analytic electroacoustical study of the spoken voice of MZ twins of prepuberal age.
The study was intended to reveal any possible analogies of the vocal spectrum and to ascertain the extent of the genetic conditioning of such analogies. For this purpose the Authors analyzed electroacustically a recorded material obtained as follows:
a) during free conversation,
b) by applying a laryngophone to the larynx in order to identify the fundamental laryngeal frequency,
c) after introducing in both cotwins a critical variant by application to the ears of a deafening tone.
Identical studies were carried out on a control material including DZ pairs and pairs of random-coupled non-related individuals very similar as to age and build.
The results can be summed up as follows:
1. The curves representing the vocal spectrum at the various frequency for each MZ pair reveal a marked similarity both in the general trend of the vocal curve and in the values at each point of the curve. The similarity is specially marked in the vicinity of the voice's fundamental frequency.
2. The location of the fundamental laryngeal frequency in the majority of MZ pairs has been found to be very close, and in many cases even coincidental.
3. Neither the analogies in the vocal spectrum nor the location of the fundamental frequency have been significantly modified by deafening.
4. The control material (including DZ pairs and random-coupled pairs of individuals having different heredity but similar as to age and build) has revealed marked dissimilarities both in the curves of the vocal spectrum and in the location of the fundamental laryngeal frequency.
On the basis of these results the Authors conclude that there is a similarity in the spoken voice of MZ pairs of prepuberal age they have examined, and this similarity is to be largely ascribed to morphological and functional factors of similarity of a genetic nature in the laryngeal generator.