Vocal-Tract Resonances as Indexical Cues in Rhesu

resonances, or formants [15]. Formants are not only important phonetic elements of speech—allowing us to distinguish different vowel sounds—but also carry important information related to the physical character-istics of the particular speaker. In humans, both in which the glottal-pulse rate and all other acoustic vari-ables (e.g., duration and amplitude envelope) were held constant while the formant frequencies were shifted up or down. Figure 1A shows the spectrograms of a single coo synthesized with two different vocal-tract lengths (10 cm and 5.5 cm). Note how the formants shift down and become more concentrated for large vocal-tract lengths and shift up and spread out for short vocal-trac