Orientation illusions and heart-rate changes during short-radius centrifugation

Area of Science:

• Space medicine
• Human physiology
• Vestibular system research

Background:

• Prolonged weightlessness causes adverse physiological effects.
• Intermittent short-radius centrifugation is a potential countermeasure.
• Understanding sensory disturbances during centrifugation is crucial for its application.

Purpose of the Study:

• To investigate the sensory effects of head movements during centrifugation.
• To assess the feasibility of using centrifugation as a spaceflight countermeasure.
• To analyze subjective sensations and compare them with semicircular canal models.

Main Methods:

• Twenty subjects performed yaw and pitch head movements while rotating at a constant angular velocity.
• Subjects were positioned supine with their heads at the centrifuge's axis of rotation.
• Heart rate was monitored, and subjective sensations of body tilt were recorded.

Main Results:

• Head movements induced transient heart rate elevation.
• All subjects reported head-contingent sensations of body tilt, despite remaining supine.
• Subjective sensations largely aligned with semicircular canal response models, but with notable deviations.
• Significant inter-individual variability in the direction, magnitude, and quality of illusory tilt was observed.

Conclusions:

• Head movements during centrifugation elicit predictable yet variable illusory sensations.
• These findings are critical for screening individuals and predicting tolerance to centrifugation.
• Further research is needed to refine models and understand the observed deviations.