The perceptual effect of air sacs

This paper presents work on air sacs that extends the work presented by de Boer, (2008a). In that paper, and before (Fitch, 2000) air sacs were identified as a likely feature of our evolutionary ancestors that may have been lost because of the evolution of speech. In the mean time, a more accurate understanding of air sac acoustics has been achieved (de Boer, 2008b; Riede et al., 2008). Ape-like air sacs modify the acoustics of a vocal tract in three ways: they add a lowfrequency resonance (near the resonance frequency of the air sac itself), they shift up the resonances of the vocal tract without the air sac, and they shift these resonances closer together. The question that is addressed in the present paper is how these changes influence perception of the difference between vocalizations.