While humans use their voice mainly for communicating information about the world, paralinguistic cues in the voice signal convey rich dynamic information about a speaker's arousal and emotional state, and extralinguistic cues reflect more stable speaker characteristics including identity, biological sex and social gender, socioeconomic or regional background, and age. Here we review the anatomical and physiological bases for individual differences in the human voice, before discussing how recent methodological progress in voice morphing and voice synthesis has promoted research on current theoretical issues, such as how voices are mentally represented in the human brain. Special attention is dedicated to the distinction between the recognition of familiar and unfamiliar speakers, in everyday situations or in the forensic context, and on the processes and representational changes that accompany the learning of new voices. We describe how specific impairments and individual differences in voice perception could relate to specific brain correlates. Finally, we consider that voices are produced by speakers who are often visible during communication, and review recent evidence that shows how speaker perception involves dynamic face-voice integration. The representation of para- and extralinguistic vocal information plays a major role in person perception and social communication, could be neuronally encoded in a prototype-referenced manner, and is subject to flexible adaptive recalibration as a result of specific perceptual experience. WIREs Cogn Sci 2014, 5:15-25. doi: 10.1002/wcs.1261 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Purpose To determine the relative importance of acoustic parameters (fundamental frequency [F0], formant frequencies [FFs], aperiodicity, and spectrum level [SL]) on voice gender perception, the authors used a novel parameter-morphing approach that, unlike spectral envelope shifting, allows the application of nonuniform scale factors to transform formants and more direct comparison of parameter impact. Method In each of 2 experiments, 16 listeners with normal hearing (8 female, 8 male) classified voice gender for morphs between female and male speakers, using syllable tokens from 2 male–female speaker pairs. Morphs varied single acoustic parameters (Experiment 1) or selected combinations (Experiment 2), keeping residual parameters androgynous, as determined in a baseline experiment. Results The strongest cue related to gender perception was F0, followed by FF and SL. Aperiodicity did not systematically influence gender perception. Morphing F0 and FF in conjunction produced convincing changes in perceived gender—changes that were equivalent to those for Full morphs interpolating all parameters. Despite the importance of F0, morphing FF and SL in combination produced effective changes in voice gender perception. Conclusions The most important single parameters for gender perception are, in order, F0, FF, and SL. At the same time, F0 and vocal tract resonances have a comparable impact on voice gender perception.

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The perception of emotions is often suggested to be multimodal in nature, and bimodal as compared to unimodal (auditory or visual) presentation of emotional stimuli can lead to superior emotion recognition. In previous studies, contrastive aftereffects in emotion perception caused by perceptual adaptation have been shown for faces and for auditory affective vocalization, when adaptors were of the same modality. By contrast, crossmodal aftereffects in the perception of emotional vocalizations have not been demonstrated yet. In three experiments we investigated the influence of emotional voice as well as dynamic facial video adaptors on the perception of emotion-ambiguous voices morphed on an angry-to-happy continuum. Contrastive aftereffects were found for unimodal (voice) adaptation conditions, in that test voices were perceived as happier after adaptation to angry voices, and vice versa. Bimodal (voice + dynamic face) adaptors tended to elicit larger contrastive aftereffects. Importantly, crossmodal (dynamic face) adaptors also elicited substantial aftereffects in male, but not in female participants. Our results (1) support the idea of contrastive processing of emotions (2), show for the first time crossmodal adaptation effects under certain conditions, consistent with the idea that emotion processing is multimodal in nature, and (3) suggest gender differences in the sensory integration of facial and vocal emotional stimuli.

Voice morphing is a powerful tool for exploratory research and various applications. A temporally variable multiaspect morphing is extended to enable morphing of arbitrarily many voices in a single step procedure. The proposed method is implemented based on interference-free representations of periodic signals and found to yield highly-naturally sounding manipulated voices which are useful for investigating human perception of voice. The formulation of the proposed method is general enough to be applicable to other representations and easily modified depending on application needs.