Dissociating mechanisms of heart-voice coupling
In a landmark paper in JASA, Orlikoff & Baken (1989a) demonstrated that the heartbeat carries through acoustic features of the human voice. Heart-voice coupling questions how vocal control is functionally regulated and has many potential engineering applications to extract heart rate from the human voice. However, laboratory phonology and bioacoustics seem to have forgotten about the phenomenon, such that its physiological underpinnings have been left unexplained. The current contribution showed that vocal acoustics contain signatures of the heartbeat as originally reported by Orlikoff & Baken (1989a). More specifically, the steady-state vowel vocalizations of 17 participants were analysed and a significant relationship between the vocal acoustic envelope and the cardiac activity (ECG) was found. Furthermore, two empirical tests were conducted to discriminate between vocal fold (vascularization) and pulmonary (heart-lung interaction) mechanisms of heart-voice coupling. In addition to a stable heart-voice coupling, a significant heart-expiration coupling during conditions of silent expiration was also found. Since the vocal folds are abducted during expiration, this result demonstrated that pulmonary mechanisms that modulate expiratory flow must be involved in heart-voice coupling. It is speculated that the hearts rhythm may be a weakly coupled pattern generator that possibly shaped the evolution of vocal and speech production.