The perceptual effects of manipulating nonlinear phenomena in synthetic nonverbal vocalizations

The communicative role of nonlinear vocal phenomena remains poorly understood since they are difficult to manipulate or even measure with conventional tools. In this study parametric voice synthesis was employed to add pitch jumps, subharmonics/sidebands, and chaos to synthetic human nonverbal vocalizations. In Experiment 1 (86 participants, 144 sounds), chaos was associated with lower valence, and subharmonics with higher dominance. Arousal ratings were not noticeably affected by any nonlinear effects, except for a marginal effect of subharmonics. These findings were extended in Experiment 2 (83 participants, 212 sounds) using ratings on discrete emotions. Listeners associated pitch jumps, subharmonics, and especially chaos with aversive states such as fear and pain. The effects of manipulations in both experiments were particularly strong for ambiguous vocalizations, such as moans and gasps, and could not be explained by a non-specific measure of spectral noise (harmonics-to-noise ratio) – that is, they would be missed by a conventional acoustic analysis. In conclusion, listeners interpret nonlinear vocal phenomena quite flexibly, depending on their type and the kind of vocalization in which they occur. These results showcase the utility of parametric voice synthesis and highlight the need for a more fine-grained analysis of voice quality in acoustic research.