Dissecting self-voice perception: From bone conduction to robotically-induced self-other voice misattribution in healthy listeners

Inspired by the prominent theory suggesting that auditory-verbal hallucinations (AVH) - the sensation of hearing voices without present speakers - arise as misattribution of inner speech towards external agents, my thesis revolved around self-voice perception and the experimental attempts of self-other voice misattribution in a healthy, non-hallucinating population, potentially mimicking the AVH phenomenology.

In the first part of my thesis, I investigated behavioral (Study 1) and neural (Study 2) underpinnings of self-other voice discrimination (SOVD). Compared to other self-related processes, self-voice perception has been investigated to a surprisingly lesser extent. Namely, self-voice research has been thwarted by the inability to experimentally match self-voice recordings to the natural sound of our voice that is altered by bone conduction. In a series of five experiments, I showed that this discrepancy can be reduced by presenting self-voice stimuli through a commercial bone conduction headset, thereby rendering self-voice as an essentially multi-modal construct. My data further shows that self-voice recognition differs from the recognition of familiar voices, however, that it still involves some familiarity processing. In addition, I explored the roles other-voice familiarity and acoustic similarity to other voice play in SOVD. Finally, I identified a self-voice specific EEG pattern, around 345 milliseconds after stimulus onset, that followed the initial auditory cortex activation, discriminated the self-voice from the voice of another unfamiliar person, and activated an extended network involving the cingulate cortex, insula, and medial temporal lobe structures. Moreover, this network was recruited less frequently with self-voices presented through bone conduction, and the occurrence of the network negatively correlated with SOVD task performance.

Based on these methodological, behavioral, and neural findings in SOVD, in the second part of my thesis, I tried to experimentally induce specific misattributions of self-towards-other voices, following the prominent theory linking AVH with self-monitoring deficits. In order to do so, I combined the aforementioned SOVD task with a robotic procedure able to engender mild hallucinations in healthy individuals by perturbing bodily self-monitoring mechanisms. With such a procedure, I managed to alter self-voice perception of healthy participants (Study 3), what I further related to breathing (Study 4). Finally, I managed to induce identity-specific AVH in healthy individuals (Study 5), as quantified by the false alarm rate in a voice detection task, thereby contributing to the understanding of the mechanisms underlying AVH and relating them to impairments in bodily self-monitoring.

Laying at the intersection of three sub-fields of neuroscience - voice perception, self-processing, and psychiatry - my thesis made a contribution by identifying neural correlates of SOVD, by proposing a new, multimodal perspective on self-voice-related research questions, and by demonstrating an experimental method of inducing AVH in a controlled laboratory environment. Together, my findings shed new light on the interactions between self-voice perception, sensorimotor processing, and interoception.