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Spatial Orientation of the Vestibulo-Ocular Reflex and Velocity Storage (9301047)
Principal Investigator
Research Area:
Species Studied
Scientific Name: Homo sapiens Species: Human

The otolith organs of the inner ear, the utricle and saccule, are the primary gravity sensors of the body. Activation of the otoliths by linear acceleration (including that of gravity) generates various spinal and ocular reflexes that act to maintain posture and gaze. Ocular counter-rolling (OCR) is one example of an otolith-ocular reflex in response to activation of the otoliths. When the head is tilted laterally (to the side), the eyes rotate around the line of sight. Termed OCR, this torsion is an orienting reflex that tends to align the eyes with the spatial vertical. During centrifugation, side-to-side head movements, and while turning corners, the OCR reflex orients the eyes towards the sum of the imposed accelerations from body movements and gravity. For example, when walking or driving around a bend, there is an inward linear (centripetal) acceleration that sums with gravity to create a vector that is tilted into the turn. This is called the gravitoinertial acceleration (GIA) vector. Recent work has shown that rolling the head and eyes towards alignment with this tilted GIA vector plays a role in maintaining balance and gaze when walking around sharp turns.

The semicircular canals in the inner ear, which sense angular acceleration of the head, also induce torsional eye movements during rapid head movements; but these responses are transient. In contrast, otolith-induced OCR responses are sustained during static tilts of the head or the GIA vector, with a gain (amount of ocular torsion/head tilt angle) of approximately 0.1. The magnitude of OCR is related to the angle of head tilt.

Deconditioning of otolith-mediated spinal and ocular reflexes following adaptation to microgravity has been proposed as the basis of many of the postural, locomotor, and gaze control problems experienced by returning astronauts. Consequently, OCR has been used in many postflight studies to gauge the effect of microgravity exposure on otolith function. There is evidence that OCR is reduced postflight in about 75% of astronauts tested; but the data are sparse, primarily due to difficulties in recording torsional eye movements. OCR was reduced in two cosmonauts for 14 days after landing. Following the 10-day Spacelab-1 mission, OCR to leftward roll tilts was reduced by 28-56% in three subjects and was unchanged in one subject. Asymmetries in the OCR response to left and right static roll tilts were also observed. OCR was reduced by 57% in one astronaut for five days after the 1992 Russian Mir mission. OCR was also reduced in two subjects during postflight side-to-side oscillations at 0.4 and 0.8 Hz. OCR gain was depressed in four subjects following the two-week SLS-2 mission. In addition, asymmetries in OCR to left/right roll tilt were observed in all subjects studied on SLS-2. The development of video-oculography has led to significant improvements in OCR measurements in humans, compared to the techniques used in the results cited above. OCR gain, measured using video-oculography following a 30-day Mir mission, decreased in one astronaut but increased in two other astronauts who had been in space for 180 days.

Strong evidence for deficits in postflight otolith function was obtained from two monkeys following a 14-day COSMOS mission. Torsional eye position was measured postflight using a robust and accurate measure of ocular torsion (search coils). The eye movements were measured both during static roll tilt and during off-vertical axis rotation (OVAR). OVAR presents a sinusoidal linear acceleration stimulus to the otoliths suitable for averaging. There was a highly significant (70%) reduction (>2 SD) in OCR gain, which persisted over the 11 days of postflight testing. In addition, vergence of the eyes, an otolith-mediated response to front-to-back linear acceleration, was also reduced during this 11-day period. Thus, although the data are not entirely consistent, the majority of subjects tested have exhibited a decrease in their OCR response following short-duration missions. In this experiment, investigators present a direct comparison of the OCR responses during preflight, inflight, and postflight centrifugation, as well as during pre- and postflight static tilt.

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Bellossi F, Clement G, Cohen B, Cork M. EDEN: a payload dedicated to neurovestibular research for Neurolab. Acta Astronautica. 1998. Jan-Apr; 42(1-8): 59-67. []

Clement G, Berthoz A, Cohen B, Moore S, Curthoys I, Dai M, Koizuka I, Kubo T, Raphan T. Perception of the spatial vertical during centrifugation and static tilt. In: Buckey J Jr., Homick J, eds. The Neurolab spacelab mission: Neuroscience research in space. Houston, TX: National Aeronautics and Space Administration; 2003:11-17. NASA Special Publication SP-2003-535. [NTRS]

Clement G, Moore ST, Raphan T, Cohen B. Perception of tilt (somatogravic illusion) in response to sustained linear acceleration during space flight. Experimental Brain Research. 2001 June;138(4):410-8. []

Cohen B, Clement G, Moore S, Curthoys I, Dai M, Koizuka I, Kubo T, Raphan T. Adaptation to linear acceleration in Space (ATLAS) experiments: equipment and hardware. In: Buckey J Jr., Homick J, eds. The Neurolab spacelab mission: Neuroscience research in space. Houston, TX: National Aeronautics and Space Administration; 2003:279-283. NASA Special Publication SP-2003-535. [NTRS]

Highstein SM, Cohen B. Neurolab mission. Curr Opin Neurobiol. 1999. August; 9(4): 495-9. []

Moore ST, Clement G, Dai M, Raphan T, Solomon D, Cohen B. Ocular and perceptual responses to linear acceleration in microgravity: alterations in otolith function on the COSMOS and Neurolab flights. J Vestib Res. 2003;13(4-6):377-93. []

Moore ST, Clement G, Raphan T, Cohen B. Ocular counterrolling induced by centrifugation during orbital space flight. Experimental Brain Research. 2001. April; 137(3-4): 323-35. []

Moore ST, Clement G, Raphan T, Curthoys I, Koizuka I, Cohen B. The human response to artificial gravity in a weightless environment: results from the Neurolab centrifugation experiments. El-Genk ed. Conference Proceedings (CP504) of the Space and Applications International Forum-2000, Albuquerque, New Mexico, Jan 30-Feb 3 2000. American Institute of Physics; 2000.

Moore ST, Cohen B, Raphan T, Berthoz A, Clement G. Spatial orientation of optokinetic nystagmus and ocular pursuit during orbital space flight. Experimental Brain Research. 2005. January;160(1):38-59. []

Moore ST, Diedrich A, Biaggioni I, Kaufmann H, Raphan T, Cohen B. Artificial gravity: a possible countermeasure for post-flight orthostatic intolerance. Acta Astronautica. 2005. May-Jun;56(9-12):867-76.[]

Adaptation, physiological
Eye movements
Gravity perception
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Data Information
Data Availability
Archive is complete. Data sets are not publicly available but can be requested.
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Angular velocity
Gravitoinertial acceleration (GIA)
Interaural linear acceleration (G)
Ocular counter-rolling (OCR) (degrees)
Tilt angle (degrees)
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
STS-90 04/17/1998 05/03/1998 16 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Pamela A. Bieri
Institutional Support
Alternate Experiment Name
Adaptation to Linear Acceleration in Space (ATLAS)
Body Rotation Device (BRD)
ESA Developed Elements for Neurolab (EDEN)
Visual and Vestibular Investigation System (VVIS)
Proposal Date
Proposal Source