Altered Peripersonal Space Boundaries in Schizophrenia: A Virtual Reality Study
Altered Peripersonal Space Boundaries in Schizophrenia: A Virtual Reality Study Hyeon-Seung Lee Peripersonal space (PPS) refers to a space encompassing a person’s physical body boundary and adjacent space, which is vital for the subjective experience of self and shapes one’s interaction with the external environment. Thus, PPS is central to our capacity to distinguish self from other. Degraded or porous self-boundary and abrupt changes in the perception of body parts that constitute the core of bodily self-disturbances in schizophrenia (SZ) may be framed as a problem of the PPS. However, it has been difficult to empirically investigate such phenomenological experiences. The present study aimed to quantify self-disturbances in schizophrenia with a multisensory paradigm that rests upon the fact that the defining feature of the PPS is the rapid integration of tactile processing with visual or auditory stimuli if they occur within the PPS, and therefore, it is possible to estimate the extent of the PPS by locating the distance from the body at which multisensory facilitation occurs. We sought to compare SZ and matched control participants (CO) with respect to estimated PPS in relation to relevant clinical measures. In this immersive virtual reality (VR) study, 24 participants with SZ and 24 demographically matched CO were instructed to respond as fast as possible to a tactile stimulus (vibration) delivered on their hand, while a task-irrelevant visual stimulus (a ball) was thrown towards the participant from different perceived distances. Past studies have documented that the tactile response time (RT) drops suddenly when the visual stimulus is presented close to the participant, indicating a significant facilitation of multisensory integration at the border of the PPS. Furthermore, the potential effect of social context on PPS was investigated by presenting the ball as thrown a mechanical launcher (i.e., non-social condition) or an avatar (i.e., social condition). Using this methodology, the spatial properties of PPS was estimated (e.g. extent or size as well as the slope of the transition between self and other). In addition, clinical psychological assessments were administered to both groups in order to relate PPS estimates to subjectively experienced self-disturbances. Results indicate that PPS for SZ was tighter than for CO regardless of the social context; this suggests a compact size of the bodily self-boundary in schizophrenia. Interestingly, the slope of the PPS for SZ was shallower in the social than nonsocial condition. This finding suggests that when individuals with schizophrenia interact with others, there is a very broad band of space wherein the capacity for self-other distinction is diminished (i.e. diffuse or fuzzy self-other boundary). Social context also increased the rate of commission errors (false alarms) in SZ, which might reflect an overestimation of the speed of the approaching object. Clinical and psychological measures were not clearly associated with the PPS findings. To summarize, this study utilized a multisensory task to estimate the extent and shape of one’s PPS. PPS representation was contracted towards the self in SZ with a shallow slope in the social interpersonal context. These findings are intriguing and point to future studies that should systematically investigate the relationship between objective and subjective measures of the bodily self in relation to psychopathology.