Wearable Haptics for Somatosensory Perception and Self-consciousness

Recent research has highlighted the crucial role of the processing of somatosensory signals involving the torso for global aspects of Bodily Self Consciousness (BSC), i.e., the experience of the conscious "I" as embodied and localized within bodily space. Compared to advances in hand or finger-based haptic interfaces, current haptic technology for the torso is relatively underdeveloped as its operations are limited to stationary conditions and laboratory environments. My thesis aims to design, implement and validate novel torso-worn tactile displays to investigate BSC in healthy individuals with specific emphasis on robot-induced presence hallucination (PH, illusory experience of feeling someone behind) and tactile gait agency. First, I examined if torso-worn haptic interfaces can be used to induce specific alterations of BSC (passivity, self-touch, and PH) in healthy individuals by adapting a robotic system and paradigm previously established by our lab (Blanke et al. 2014) to the torso-worn haptic interface. In a feasibility study in healthy individuals, a torso-worn vibrotactile display (Study1) successfully induced the illusory sensations of being touched (passivity experience). Next, I developed CognoVest, a portable, torso-worn force interface that I designed to provide human-like poking stimuli on the user's back. Study 2 confirms the induction of illusory self-touch and passivity experiences by CognoVest and the induction of PH of mild to moderate intensity in healthy individuals. In Study 3, I extended the use of torso-worn haptic interfaces to the research on conscious action monitoring and investigated the sense of agency (SoA; a core aspect of BSC) for the entire body. To this aim, I developed the FeetBack system that examines the sensorimotor perception of tactile action consequences during locomotion, as previously tested by our lab for auditory and visual action consequences. Study 3 extends prior findings on the auditory or visual gait agency to the sense of touch and shows that delayed re-mapped tactile feedback systematically modulates SoA for walking. Finally, I examined and compared tactile spatial discrimination on the human back (Study 4) for force and vibrotactile stimulation, using interfaces realized in Study 2 and 3, thus providing a first direct (within-participant) evaluation of such interfaces. At the intersection of haptics and behavioral neuroscience, my thesis makes contributions by taking the first steps towards the design, and validation of torso-worn haptic interfaces as well as their applications in stationary/mobile sensorimotor experimentation settings. My findings for tactile perception on the back suggest that designers can use force stimulators to design the torso-worn tactile interface to provide more ecological touch feedback with an (almost) similar level of tactile spatial discrimination accuracy as observed in widespread vibrotactile interfaces. I applied this approach to the design of the CognoVest that induced systematic change in self-other distinctions. Results with CognoVest might have important implications for developing wearable therapeutic devices to down-regulate specific psychotic symptoms in patients with PH experiences. Moreover, I showed that healthy walkers had strong SoA for remapped tactile feedback, suggesting that the FeetBack system could potentially be used to enhance gait awareness in patients with gait deficits.