Image right: Gaze-holding measurements in pitch

The Gaze Laboratory is also interested in investigating ways to evaluate changes in visual-vestibular performance as a method to determine the effectiveness of select countermeasures, and parameters that can tell us about when astronauts can be returned to flight or daily activities. For example, clear vision and accurate localization of objects in the environment are prerequisites for reliable performance of motor tasks. Space flight confronts the crewmember with a stimulus rearrangement that requires adaptation in order to function effectively with the new requirements of altered spatial orientation and motor coordination. Adaptation and motor learning driven by the effects of cerebellar disorders may share some of the same demands that face our astronauts. One measure of spatial localization shared by the astronauts and those suffering from cerebellar disorders that is easily quantified, and for which a neurobiological substrate has been identified, is the control of the angle of gaze (the line of sight). The disturbances of gaze control that have been documented to occur in astronauts, both inflight and postflight, can be directly related to changes in the extrinsic gravitational environment and intrinsic proprioceptive mechanisms thus, lending themselves to description by mathematical models. The basic models can be formulated using normal, non-astronaut test subjects and subsequently extended by studying abnormalities of gaze control in patients with cerebellar disease. Finally, tests of astronaut subjects during and after exposure to space flight, in association with the corresponding sensory-motor adaptations, will allow us to evaluate and extend our developed understanding of adaptation in the control of eccentric gaze-holding. This in turn will be instrumental in developing simplified techniques to measure adaptation to flight as it occurs and to determine the effects of various vestibular countermeasures as they are tested either inflight or on the ground.

Image left: Gaze-holding measurements as a function of high G-force on Pensacola centrifuge

Countermeasures for space motion sickness (SMS) can be developed using information derived from flight studies of visual-vestibular function. SMS and clear vision (associated with Vestibular-Ocular Reflex gain changes) during space flight remain problems that have no realistic solution given the current countermeasures that are available today. Existing countermeasures for SMS include: (1) Medications to control symptoms associated with microgravity, (2) Preflight adaptation, and (3) Planned centrifugation on-orbit. The pharmacological management of motion sickness symptoms has several disadvantages: (a) Drugs can only be used at specific times during a flight, (b) they cannot prevent the appearance of motion sickness symptoms, and (c) regardless of their efficacy, all drugs have side effects that are undesirable. Preflight adaptation, while it appears to be effective, requires: (a) substantial investments in crew time and resources, and it is currently unknown about the effects of preflight adaptation during long duration flights, and (b) that crewmembers experience some level of Earth based motion sickness if the preflight adaptation environment is a serious analog of flight. Inflight centrifugation may be the ultimate vestibular countermeasure, however, (a) rapid implementation is impracticable, (b) like preflight adaptation protocols, the crewmembers will experience motion sickness on both the ground based and flight centrifuges. Therefore, the overall objective of using our knowledge of gaze function to develop a SAS countermeasure based on the effects of stroboscopic vision on preventing motion sickness, as well as preventing retinal slip, and then develop liquid crystal goggles that will serve as electronic shutters to provide a form of stroboscopic vision on motion sickness induced in laboratory settings. We will also investigate the possible mechanisms by which these goggles exert their effect.

Image right: Subject following gaze-holding on Pensacola centrifuge

To accomplish the objectives outlined above, the Gaze Laboratory has a number of hardware and software tools. Chief among these tools is a set of visual displays, including a cruciform target arrangement (luminous target) that is available to provide the visual stimulation for target acquisition, pursuit tracking, memorized head rotations, and sinusoidal head oscillations. The target arrangement can be used to provide a variety of static, time optimal, and dynamic visual stimuli to the subject in both the horizontal and vertical planes under computer control. Each axis of the target system is approximately 1.25 m long and contains a line of 495 miniature LEDs with a spacing between LEDs of 2.54 mm. Software drivers have been developed to enable concurrent or sequential illumination of "special" standard target positions in the horizontal (0°, ±20°, ±30°) and vertical (0°, ±15°, ±20°, ±30°) planes, as well as to present both sinusoidal and non-predictable, constant-velocity ramp-type target motion along either axis. The luminous target device also includes separate eccentric LEDs that can extend the targets beyond the effective oculomotor (EOM) range in both the horizontal and vertical planes.

Image left: Cruciform target configuration for measurements associated with voluntary head and eye movements.

Eye position can be obtained using two techniques available in the laboratory: standard EOG, and video camera. The video technique currently in use involves recording video images of the moving eye from a light-weight camera system that has flown (minus the attached camera) as part of both the Extended Duration Orbiter Medical Project (EDOMP) and Joint US/Russian missions. The camera images are integrated with the data from the visual display, the rate sensors, and the on/off status of the laser, recorded on a Hi-8 video recorder or digitized and processed off-line by using a maximum likelihood estimation algorithm (developed in-house).

Active head movement protocols can be supported using video capture techniques and a triaxial rate sensor system that is integrated with the EOG or video eye movement measurement systems. Special software is also available which will deal effectively with occasionally observed shifts in the velocity waveform baseline. Calibration trials using visual feedback of head position (a head-fixed laser) are used to verify the integrity of the calculated head position information.

Image right: Target acquisition on orbiter middeck during space flight

Operator interactive software has been developed that allows two basic approaches for dealing with the geometry issue when analyzing and interpreting eye and head movement data. The first technique involves comparing measured eye movements with expected eye movements, considering the geometric relationships between the eye, head, and target. This approach allows for the direct evaluation of oculomotor performance, without modifying the measured eye or head waveforms, by calculating the position of the target with respect to the eye, no matter where the eye is in its plane of motion and given the spatial relationships between the eye and head, as well as, between the head and target. The second approach involves adjusting the measured eye movement data to compensate for the contributions to the data due to the different axes of head and eye rotation. This technique standardizes the measured eye (gaze) position data by mathematically transforming it as a way that effectively relocates the eye to a more suitable reference position (such as the center of head rotation), thereby removing eye eccentricity effects. The advantage of this approach lies in the flexibility it provides to data analysis: direct comparisons of response waveforms may be made from multiple trials, both within and between subjects, by inherently accounting for trial-to-trial variations in head or target motion. We use both techniques in analyzing our active eye and head movement data.