Smiles can be conveyed to listeners via speech signals: a case study with Japanese labiodentalization

One long-standing question in speech communication research concerns the extent to which an emotional state is encoded in the acoustic signal and conveyed to the listeners. To address this question, we deployed a recent finding in Japanese, in which speakers replace bilabial sounds (e.g. [b]) with labiodental sounds (e.g. [v]) when speaking with a smile. Experiment 1 used stimuli recorded by two professional voice actors under four conditions crossing two factors, voice quality (smile vs. non-smile) and articulation (labiodental vs. bilabial). The results confirm that labiodentals function as a reliable cue for smiling, even in the absence of visual information. Experiment 2 controlled for the effects of F0 and amplitude of the stimuli, and we still observed an effect of labiodentals. We conclude (1) that smiles can be conveyed via speech signals to the listeners without any visual cues and (2) that in the case of Japanese, this can be achieved via the use of labiodentals.