Hyperventilation Effects on Bodily Self-Consciousness

Mean Rating of Perceived Breathing Location in the Virtual Body: Bodily Self-Consciousness Questionnaire Item 1 (BSC-Q1)

Self-reported agreement with the statement "It seemed as if I was feeling my respiration in the virtual body", item 1 of the Bodily Self-Consciousness Questionnaire (BSC-Q). Rated on a 7-point Likert scale from -3 (totally disagree) to +3 (totally agree); minimum -3, maximum +3. Higher scores indicate that the participant's own breathing is felt more strongly to be located in the virtual body (a stronger illusion). This is a mechanistic outcome; neither a higher nor a lower score is a better or worse clinical outcome. Rated after each of the 6 virtual reality (VR) exposures (2 normal-breathing exposures, 4 hyperventilation cycles); the two hyperventilation cycles at each synchrony level are averaged within participant. Reported as the mean rating in each of the 4 conditions (Synchronous/Asynchronous x Normal breathing/Hyperventilation). Primary analysis: the Synchrony x Breathing interaction in a within-subjects linear mixed-effects model.

Mean Drift in Perceived Self-Location Toward the Virtual Body, Measured With the Mental Imagery Task (MIT)

Behavioural measure of perceived self-location, reported in centimetres. Participants stand still in virtual reality and watch a ball approach along the anterior-posterior body axis; the ball then disappears and they press a button when they imagine it reaching their own position. The position of the hidden ball along that axis at the moment of the button press is recorded as the estimate of perceived self-location (method of Nakul et al., Sci Rep 2020;10:6802, which records self-location as an anterior-posterior coordinate and reports drifts in centimetres). One value is reported per participant per condition: the drift, calculated as the coordinate recorded after the VR exposure minus the participant's own matched breathing-state pre-test coordinate. Positive values indicate relocation toward the virtual body; larger positive values indicate a stronger illusion. Secondary endpoint, analysed as the Synchrony x Breathing interaction in a mixed-effects model.

Mean Rating of Perceived Breathing Synchrony With the Virtual Body: Bodily Self-Consciousness Questionnaire Item 2 (BSC-Q2)

Self-reported agreement with the statement "I felt as if the virtual body was breathing with me", item 2 of the Bodily Self-Consciousness Questionnaire (BSC-Q). Rated on a 7-point Likert scale from -3 (totally disagree) to +3 (totally agree); minimum -3, maximum +3. Higher scores indicate a stronger sense that the virtual body was breathing together with the participant. This is a mechanistic outcome; neither a higher nor a lower score is a better or worse clinical outcome. Rated after each of the 6 virtual reality (VR) exposures (2 normal-breathing exposures, 4 hyperventilation cycles); the two hyperventilation cycles at each synchrony level are averaged within participant. Reported as the mean rating in each of the 4 conditions (Synchronous/Asynchronous x Normal breathing/Hyperventilation). Secondary endpoint, analysed with a mixed-effects model analogous to the primary endpoint and reported with uncorrected p-values.

Mean Rating of Self-Identification With the Virtual Body: Bodily Self-Consciousness Questionnaire Item 3 (BSC-Q3)

Self-reported agreement with the statement "I felt as if the virtual body was my body", item 3 of the Bodily Self-Consciousness Questionnaire (BSC-Q). Rated on a 7-point Likert scale from -3 (totally disagree) to +3 (totally agree); minimum -3, maximum +3. Higher scores indicate stronger self-identification with the virtual body. This is a mechanistic outcome; neither a higher nor a lower score is a better or worse clinical outcome. Rated after each of the 6 virtual reality (VR) exposures (2 normal-breathing exposures, 4 hyperventilation cycles); the two hyperventilation cycles at each synchrony level are averaged within participant. Reported as the mean rating in each of the 4 conditions (Synchronous/Asynchronous x Normal breathing/Hyperventilation). Secondary endpoint, analysed with a mixed-effects model analogous to the primary endpoint and reported with uncorrected p-values.

Mean Rating of Being Located Outside the Physical Body: Bodily Self-Consciousness Questionnaire Item 4 (BSC-Q4)

Self-reported agreement with the statement "I felt as if I was outside my physical body", item 4 of the Bodily Self-Consciousness Questionnaire (BSC-Q). Rated on a 7-point Likert scale from -3 (totally disagree) to +3 (totally agree); minimum -3, maximum +3. Higher scores indicate a stronger sensation of being located outside the physical body. This is a mechanistic outcome; neither a higher nor a lower score is a better or worse clinical outcome. Rated after each of the 6 virtual reality (VR) exposures (2 normal-breathing exposures, 4 hyperventilation cycles); the two hyperventilation cycles at each synchrony level are averaged within participant. Reported as the mean rating in each of the 4 conditions (Synchronous/Asynchronous x Normal breathing/Hyperventilation). Secondary endpoint, analysed with a mixed-effects model analogous to the primary endpoint and reported with uncorrected p-values.