Investigating Techniques to Enhance the Sense of Embodiment in Immersive Virtual Reality

Virtual Embodiment Questionnaire (VEQ) Subscale Scores (Ownership, Agency, Perceived Change in Body Representation)

Embodiment-related self-report assessed with the Virtual Embodiment Questionnaire (VEQ). Three subscale scores are computed: Ownership, Agency, and Perceived Change in Body Representation. Each subscale score is calculated as the mean of 4 items rated on a 7-point Likert scale (1 = strongly disagree to 7 = strongly agree). Higher scores indicate stronger perceived ownership of the virtual body (Ownership), greater sense of control over the virtual body/actions (Agency), and stronger perceived change in body representation during VR (Perceived Change in Body Representation).

Virtual Environment Light Test: Mean Reaction Time by Body vs Environment Locations

Participants perform a VR reaction-time task in which brief light stimuli are presented at predefined locations: on the avatar's right upper limb, left upper limb, right lower limb, left lower limb, or in the virtual environment outside the avatar. Stimuli occur at randomized intervals (1-5 seconds). Participants respond as quickly as possible when a light appears. The outcome is the mean reaction time (milliseconds) computed separately for each stimulus location category. Location-specific averages are used to capture potential asymmetries relevant to the clinical groups (e.g., right/left differences in stroke due to hemiparesis, and upper vs lower limb differences in spinal cord injury due to predominant lower-limb impairment).

Electrodermal Activity (EDA) during VR conditions

Electrodermal activity (EDA), a measure of sympathetic arousal, includes a tonic component (skin conductance level, SCL) and a phasic component (skin conductance responses, SCR). EDA is recorded during the VR sessions. For each VR condition, EDA metrics are computed relative to the baseline. The tonic component is summarized as the mean SCL during the condition. Phasic activity is summarized by SCR measures, including the number of SCR peaks and the mean SCR peak amplitude during the condition. Baseline-referenced values are computed as change from baseline for each metric.

Skin Temperature During Virtual Reality Conditions

Chest skin temperature will be analyzed as a slow physiological indicator that may vary with embodiment-related experiences in VR; based on prior findings, decreases in peripheral skin temperature have been reported with stronger embodiment. For each VR condition, skin temperature will be summarized as the mean value and condition values will be expressed relative to the baseline period (change from baseline).

Heart Rate Variability (HRV) From ECG During VR Conditions

Electrocardiogram (ECG) is recorded continuously during each study session; on Day 1 and Day 3, the ECG-derived heart rate is also used to provide real-time heart-rate visual biofeedback in VR. R-peaks are detected to derive the RR-interval time series, with artifact beat correction prior to analysis. Heart rate variability (HRV) is quantified for each VR condition and compared with baseline. Planned HRV metrics include standard time-domain indices (e.g., mean RR, SDNN, RMSSD) and frequency-domain indices (e.g., LF and HF power and LF/HF ratio). In the literature, HRV frequency components have been reported as sensitive to embodiment-related manipulations, with higher LF activity associated with lower embodiment and higher HF activity associated with moderate/high embodiment.