Acute stress affects peripersonal space representation

Peripersonal space (PPS) is the region of space surrounding the body. It has a dedicated multisensory-motor representation, whose purpose is to predict and plan interactions with the environment, and which can vary depending on environmental circumstances. Here, we investigated the effect on the PPS representation of an experimentally induced stress response. We assessed PPS representation in healthy humans, before and after a stressful manipulation, by quantifying visuotactile interactions as a function of the distance from the body, while monitoring salivary cortisol concentration. Participants, who showed a cortisol stress response, presented enhanced visuotactile integration for stimuli close to the body and reduced for far stimuli. Conversely, individuals, with a less pronounced cortisol response, showed a reduced difference in visuotactile integration between the near and the far space. In our interpretation, physiological stress resulted in a freezing-like response, where multisensory-motor resources are allocated only to the area immediately surrounding the body.

Experience-Dependent Modulation of Rubber Hand Illusion in Badminton Players

Badminton players have a plastic modification of their arm representation in the brain due to the prolonged use of their racket. However, it is not known whether their arm representation can be altered through short-term visuotactile integration. The neural representation of the body is easily altered when multiple sensory signals are integrated in the brain. One of the most popular experimental paradigms for investigating this phenomenon is the “rubber hand illusion.” This study was designed to investigate the effect of prolonged use of a racket on the modulation of arm representation during the rubber hand illusion in badminton players. When badminton players hold the racket, their badminton experience in years is negatively correlated with the magnitude of the rubber hand illusion. This finding suggests that tool embodiment obtained by the prolonged use of the badminton racket is less likely to be disturbed when holding the racket.

Disruption by virtual reality of the cortical oscillations related to visuotactile integration during an embodiment process

Virtual reality (VR) enables fast, free, and highly controllable experimental body image setting. Illusions pertaining to a body, like the rubber hand illusion (RHI), can be easily conducted in VR settings, and some phenomena, such as full-body illusions, are only realized in virtual environments. However, the multisensory integration process in VR is not yet fully understood, and we must clarify the limitations and whether specific phenomena can also occur in real life or only in VR settings. One useful investigative approach is measuring brain activities during a psychological experiment. Electroencephalography (EEG) oscillatory activities provide insight into the human multisensory integration process. Unfortunately, the data can be vulnerable to VR noise, which causes measurement and analytical difficulties for EEG data recorded in VR environments. Here, we took care to provide an experimental RHI setting using a head-mounted display, which provided a VR visual space and VR dummy hand along with EEG measurements. We compared EEG data taken in both real and VR environments and observed the gamma and theta band oscillatory activities. Ultimately, we saw statistically significant differences between congruent (RHI) and incongruent (not RHI) conditions in the real environment, which agrees with previous studies. No difference in the VR condition could be observed, suggesting that the VR setting itself altered the perceptual and sensory integration mechanisms. Thus, we must model this difference between real and VR settings whenever we use VR to investigate our bodily self-perception.

The Effect of Visual Capture Towards Subjective Embodiment Within the Full Body Illusion

Typically, multisensory illusion paradigms emphasise the importance of synchronous visuotactile integration to induce subjective embodiment towards another body. However, the extent to which embodiment is due to the ‘visual capture’ of congruent visuoproprioceptive information alone remains unclear. Thus, across two experiments (total N = 80), we investigated how mere visual observation of a mannequin body, viewed from a first-person perspective, influenced subjective embodiment independently from concomitant visuotactile integration. Moreover, we investigated whether slow, affective touch on participants’ own, unseen body (without concomitant touch on the seen mannequin) disrupted visual capture effects to a greater degree than fast, non-affective touch. In total, 40% of participants experienced subjective embodiment towards the mannequin body following mere visual observation, and this effect was significantly higher than conditions which included touch to participants own, unseen body. The velocity of the touch that participants received (affective/non-affective) did not differ in modulating visual capture effects. Furthermore, the effects of visual capture and perceived pleasantness of touch was not modulated by subthreshold eating disorder psychopathology. Overall, this study suggests that congruent visuoproprioceptive cues can be sufficient to induce subjective embodiment of a whole body, in the absence of visuotactile integration and beyond mere confabulatory responses.