Background

An implicit understanding of one’s body with fixed boundaries allows us to differentiate self from other. However, individuals with schizophrenia (SZ) frequently report experiencing bodily self-disturbances such as sudden changes in size and shape of the body and flexible or porous body boundary. In order to quantify bodily disturbances in schizophrenia, we investigated the construct of peripersonal space (PPS), which represents the ‘near’space immediately surrounding our bodies. Whilst the physical body boundary is fixed, the neural representation of PPS is plastic and can be estimated using multisensory integration paradigms. Moreover, the size and extent of the PPS is thought to be influenced by the social-emotional environment, which in turn has implications for social interactions. We sought to measure PPS in SZ and control participants (CO) by adopting a multisensory integration task in a virtual reality (VR) environment to test whether PPS is altered in SZ when compared to CO. In addition, we examined the effects of social context and threat on the plasticity of PPS.

Methods

SZ and demographically matched CO participated in a visual-tactile response time (RT) task in immersive VR. Participants wore a head-mounted display and trackers on their feet, hands, and the torso. Handheld controllers were used to deliver tactile vibration and to record RTs. In VR, participants faced either an avatar or a machine that threw a ball at a speed of 3m/s. In addition to this visual display, tactile vibration was delivered to the participant’s hand via the controller at one of five set distance points from the initiation of the ball pitch. Participants were asked to press a trigger on the controller as soon as they felt a vibration. There were two social conditions (ball thrown by a person or a machine) and two emotion conditions (threat versus no threat). The RTs were recorded. According to Serino et al (2018), visuo-tactile integration would facilitate the RT nearer one’s PPS boundary. We calculated the location where the visuotactile facilitation occurs to estimate the boundary of PPS. In addition, we examined positive and negative symptoms, social isolation, and social functioning.

Results

PPS boundary in SZ differed significantly from that of the CO. However, there were a range of individual differences in PPS within groups. RTs were faster for threat than non-threat stimuli. The impact of social context was not conclusive.

Discussion

Preliminary results suggest that PPS can be estimated in VR and that PPS is altered in SZ. Given the importance of PPS in the construction of social self, anomalous experience of PPS in SZ may contribute to self-disturbances. Moreover, individual differences in PPS might impact social interactions and hence contribute to social impairments in schizophrenia.