Involvement of the left insula in the ecological validity of the human voice

A subtle difference between a real human and an artificial object that resembles a human evokes an impression of a large qualitative difference between them. This suggests the existence of a neural mechanism that processes the sense of humanness. To examine the presence of such a mechanism, we compared the behavioral and brain responses of participants who listened to human and artificial singing voices created from vocal fragments of a real human voice. The behavioral experiment showed that the song sung by human voices more often elicited positive feelings and feelings of humanness than the same song sung by artificial voices, although the lyrics, melody, and rhythm were identical. Functional magnetic resonance imaging revealed significantly higher activation in the left posterior insula in response to human voices than in response to artificial voices. Insular activation was not merely evoked by differences in acoustic features between the voices. Therefore, these results suggest that the left insula participates in the neural processing of the ecological quality of the human voice.