– Pavo Orepic, 27th February, 2020
I am a part of the Laboratory of Cognitive Neuroscience, led by Prof Olaf Blanke, at the Swiss Federal Institute of Technology. In our Lab, we started a “Hallucination Engineering” group. The overall concept is an induction of a psychosis-like state in healthy individuals, with the goal of “reverse engineering” the hallucination process. Specifically, we have a robotic device, which facilitates spatiotemporal sensorimotor conflicts between upper limb movement and somatosensory feedback on the back. Participants perform forward-backward poking movements, which are translated into touch sensations on their back, with the possibility of controlling for the force and the delay of the accompanying somatosensory feedback. While being exposed to such sensorimotor stimulation, participants report experiencing agency loss or even other-agency sensations, thought to result from erroneous feed-forward signaling between actions and accompanying sensory reafferences.
With this robotic device, we can create various degrees of spatiotemporal conflicts, and accordingly observe a differential effect on subjective experience. Thus, in a state of a higher conflict, healthy participants experience higher somatic passivity – attaching sensations imposed on one’s body to an external cause – and stronger presence hallucination – the sensation of having someone nearby when no one is actually present. The work of our group uses neuroimaging work – both EEG and fMRI – to investigate the neural underpinnings of our robotically-induced psychosis like state. Moreover, it has clinical applications, where we try to draw a parallel to the experience and neural activations underlying hallucinatory states of both psychiatric and neurological patients, especially those suffering from Parkinson’s disease, as they are known to be affected by the presence hallucination the most.
My work extends this research by exploring the changes in auditory perception, specifically voice perception, in the aforementioned psychosis-like state. The goal of my PhD is to find behavioral patterns and explore the related neural mechanisms of self-other vocal misattribution, potentially occurring in the state evoked by our robotic system and resembling auditory verbal hallucinations (AVH) – defined as hearing voices with the absence of a speaker.
Recent work suggests AVH arises because internal ‘subvocalizations’ are mistaken to be coming from an external source (or agent). As our robotic manipulation creates a non-existing alien agent, an “other”, who we believe to arise as a change in the mechanisms of bodily self-consciousness – involving conflicting sensorimotor integration – I wanted to investigate whether this conflict could be reflected in the vocal domain, as a bias to hear the “other” voice in vocally ambiguous situations. My work encompasses exploring both passive and active voice perception (i.e. voice production), with and without the additional robotic sensorimotor manipulation, to unveil still poorly understood mechanisms of self-voice perception, together with the conditions under which self-voice misattribution could occur.
I also explored the relationship between the self-voice perception and processing of interoceptive signals such as respiration and heartbeat, known to contribute to the neural representation of the self. This research could extend the fundamental understanding of self-voice perception and AVH and also shed the light on the link between (a malfunctioning) self-voice perception and the brain mechanisms of sensorimotor integration.