Clinical Research Directory

Participants breathe deeper and faster than normal, maintaining continuous cyclic breathing without pauses between inhalation and exhalation, paced by a pre-recorded standardised voice guide in German or English with background music. The hyperventilation block comprises four cycles, each with a 10-minute guided paced-hyperventilation induction, a 2-minute VR exposure and a 3-minute post-exposure stack (BSC-Q, Mental Imagery Task, distress NRS); cycle 1 additionally includes a 2-minute hyperventilation-state Mental Imagery Task pre-test between the induction and the VR exposure. A 5-minute sustained-hyperventilation resting-state EEG window is collected between cycles 2 and 3, with the voice guide replaced by a soft drum pacing tone. Cumulative hyperventilation is approximately 45 minutes, followed by a single supervised recovery. EtCO2, SpO2, heart rate and heart rate variability (ECG) are monitored continuously under the protocol's tiered stop criteria.

Within-subject control condition for the Breathing factor. Participants breathe at their natural spontaneous rate while receiving audio guidance from the same pre-recorded standardised voice guide and background music used in the hyperventilation condition, so that the auditory environment is held constant across conditions and only the breathing instruction differs. Delivered as two 8-minute normal-breathing cycles (3 minutes spontaneous breathing in VR, a 2-minute VR exposure, and a 3-minute post-exposure stack of BSC-Q, Mental Imagery Task and distress NRS), one with synchronous and one with asynchronous respiratory-visual feedback, seated in the experimental chair wearing the head-mounted display.

Respiratory-visual VR paradigm delivering contingent feedback; this is the measurement method through which bodily self-consciousness is assessed. Seated participants wear a head-mounted display showing a first-person view of a three-dimensional virtual body positioned about 2 metres in front of the viewpoint and seen from behind. A respiratory belt at the level of the umbilicus drives, in real time, a luminous halo surrounding the virtual body: the halo becomes increasingly visible during inspiration, reaches maximum luminosity at peak inspiration and fades during expiration, in synchrony with the participant's actual breathing. Each exposure lasts 2 minutes (120 seconds). Each participant receives one synchronous exposure in the normal-breathing block and two in the hyperventilation block.

Respiratory-visual VR paradigm delivering non-contingent feedback; the control level of the Synchrony factor. Setup is identical to the synchronous condition (seated, head-mounted display, virtual body about 2 metres in front seen from behind, respiratory belt at the umbilicus), except that the halo modulation is phase-shifted and frequency-adjusted to 80% or 120% of the measured breathing frequency, so that the visual feedback never corresponds to the participant's respiratory state. Each exposure lasts 2 minutes (120 seconds). Each participant receives one asynchronous exposure in the normal-breathing block and two in the hyperventilation block.