VOCAL-TRACT LENGTH AND FORMANT FREQUENCY DISPERSION CORRELATE WITH BODY-SIZE IN RHESUS MACAQUES

Body weight, length, and vocal tract length were measured for 23 rhesu s macaques (Macaca mulatta) of various sizes using radiographs and com puter graphic techniques. Linear predictive coding analysis of tape-re corded threat vocalizations was used to determine vocal tract resonanc e frequencies (''formants'') for the same animals. A new acoustic vari able is proposed, ''formant dispersion,'' which should theoretically d epend upon vocal tract length. Formant dispersion is the averaged diff erence between successive formant frequencies, and was found to be clo sely tied to both vocal tract length and body size. Despite the common claim that voice fundamental frequency (F-0)provides an acoustic indi cation of body size, repeated investigations have failed to support su ch a relationship in many vertebrate species including humans. Formant dispersion, unlike voice pitch, is proposed to be a reliable predicto r of body size in macaques, and probably many other species. (C) 1997 Acoustical Society of America.