Eye movements and motion perception during off-vertical axis rotation after spaceflight

Area of Science:

• Neuroscience
• Space Physiology
• Vestibular System

Background:

• The otolith organs are crucial for sensing gravity and linear acceleration.
• Spaceflight alters the vestibular system, impacting balance and spatial orientation.
• Off-vertical axis rotation (OVAR) is a method to assess otolith function.

Purpose of the Study:

• To investigate the effects of short-duration spaceflight on otolith function using OVAR.
• To compare pre- and postflight responses to low- and high-frequency OVAR stimuli.
• To evaluate changes in perceived motion and motion sickness after space adaptation.

Main Methods:

• Eight astronauts underwent constant velocity OVAR in darkness at 0.125 Hz and 0.5 Hz before and after spaceflight.
• Eye movements were recorded using infrared videography.
• Perceived motion was assessed using a 4-DOF joystick; motion sickness was also evaluated.

Main Results:

• Low-frequency OVAR elicited tilt-related otolith responses (ocular counter-roll/pitch, conical motion perception).
• High-frequency OVAR elicited translation-related otolith responses (horizontal/vergence eye movements, cylindrical motion perception).
• Transient changes in translational ocular responses and increased motion perception sensitivity were observed postflight; tilt reflexes remained largely unchanged.

Conclusions:

• Some otolith reflexes elicited by passive motion are resilient to short-duration spaceflight or readapt rapidly.
• Postflight recovery from sensory conflict involves higher-order neural processes.
• OVAR stimuli were less provocative of motion sickness postflight, suggesting adaptation.