Dissociating mechanisms of heart-voice coupling

In a landmark paper in JASA, Orlikoff & Baken (1989a) demonstrated that the heartbeat echoes through acoustic features of the human voice. Heart-voice coupling questions how vocal control is functionally regulated under these perturbations. It has many potential engineering applications that extract heart rate from human voice and speech, with underutilized potential for cardiac monitoring from (wild) animal calls. However, laboratory phonology and bioacoustics seem to have forgotten about the phenomenon, such that the physiological underpinnings of heart-voice coupling have been left unexplained. In the current contribution, we show that vocal acoustics contain signatures of the heartbeat as originally reported by Orlikoff & Baken (1989a). More specifically, we analysed the steady-state vowel vocalizations of 17 participants and found a significant relationship between the vocal amplitude envelope and the cardiac activity (ECG). Furthermore, we conducted two empirical tests to dissociate between glottal (vocal fold vascularization) and subglottal (heart-lung interaction) mechanisms of heart-voice coupling. In addition to a stable heart-voice coupling, we also found a significant heart-expiration coupling during conditions of pure expiration. Since the vocal folds are abducted during expiration, this result demonstrates that subglottal mechanisms that modulate expiratory flow must be involved in heart-voice coupling. We argue that the hearts rhythm needs to be considered as a weakly coupled pattern generator that possibly shaped the evolution of vocal and speech production.