RESEARCH PROJECT ABSTRACTS
For more information on each project follow the link in each abstract.
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PROJECT
1 ABSTRACT:
Context-Specific Adaptation of Gravity-Dependent Vestibular Reflex Responses
Eye movements are important for keeping the images of objects stationary on our retinas, since visual acuity can be significantly degraded with retinal slip of only a few degrees per second. Impairment of this ability can lead to disorientation and reduced performance in sensori-motor tasks such as piloting a spacecraft. Transitions between different gravito-inertial force environments-as during different phases of space flight-provide an extreme test of the adaptive mechanisms. It is vitally important to determine the adaptive capabilities of crew members in such circumstances, so that it can be determined to what extent the sensori-motor skills acquired in one gravity environment will transfer to others. This project will begin to lay the foundation for understanding these capabilities, and for determining how science can aid the process of adaptation and readaptation. An integrated set of experiments is planned to address this issue. The project will use the general approach of adapting the vestibulo-ocular reflex (VOR) or the vestibulo-colic reflex (VCR) to a particular change in gain or phase in one condition of gravito-inertial force, and adapting to a different gain or force (or asking for no change) in a second gravito-inertial force condition, and then determining if the gravito-inertial force itself-the context clue-can recall the previously learned adapted responses. Evidence indicates that unless there is specific training to induce context-specificity, reflex adaptation is sequential rather than simultaneous. The knowledge gained from this project will advance the design of potential pre-adaptation strategies to assist flight crews in making transitions between different gravito-inertial force situations, and it can provide design data for spacecraft facilities (artificial gravity, exercise centrifuge) by delineating the limits of human adaptive capabilities.
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PROJECT 2 ABSTRACT:
Visual Orientation in Unfamiliar Gravito-Inertial Environments
The goal of this project is to develop more effective countermeasures against the orientation difficulties experienced by astronauts by understanding how humans learn to orient and navigate when movement is possible in all six degrees of freedom. On Earth, large amplitude body movements are generally constrained to a horizontal plane, and corresponding turning motions are about the gravitational vertical. In weightlessness, movement is not so constrained, and the "down" reference provided by gravity is absent. Astronauts often view the spacecraft interior from unfamiliar body orientations - upside down, for example. Seen this way, familiar objects - or people - can be difficult to recognize. It is harder to keep track of where things are around you, the direction you came from, or where you are going. Astronauts frequently experience striking "visual reorientation illusions" (VRIs), and say that the ceiling or wall or the spacecraft beneath their feet somehow seems like a floor. VRIs can trigger attacks of space motion sickness, and potentially complicate emergency escape. MIR crewmembers say that after several weeks living aboard the space station, orientation becomes easier, but some aspects of navigation remain difficult. It is thought that there are large individual differences in the ability to orient and navigate in six degrees of freedom, and that practice in simulated environments - neutral buoyancy or virtual reality simulators - may help. However, no techniques have been developed to quantify interpersonal differences in ability, or the effectiveness of spacecraft-specific or generic preflight visual orientation training. We do not yet fully understand the physiology of how orientation and navigation information is coded in the brain.
In this project, experiments are underway to quantify how visual, proprioceptive and gravireceptor cues determine orientation and spatial memory in real and virtual environments; how orientation, navigation and visual search abilities specifically depend on visual experience; how direction is neurally coded in three dimensions in animals in 1-G and parabolic flight; and whether virtual reality and related techniques can be used for astronaut preflight visual orientation training as a countermeasure against VRIs and 3-D navigation problems.
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PROJECT 3 ABSTRACT:
Major problems of space flight, in addition to adapting to microgravity, include postflight difficulties with standing, walking, turning corners and other activities that require stable upright posture and gaze stability. These difficulties also could inhibit astronauts' ability to bail out or escape from their vehicle during emergencies. The overall goal of this project is to develop quantitative, parametric approaches for assessing gaze stability and spatial orientation during normal gait and when gait is perturbed. Compared to assessments of the vestibulo-ocular reflex, analysis of vestibular effects on locomotor function is relatively less well developed and quantified. This project will address that shortcoming by applying the methodology of nonlinear orbital stability to quantify responses in a single variable and by using multivariate statistical approaches to link together the responses across separate tests. In this way, the project will exploit the information available and increase the "resolving power" to discriminate between normal and pathological responses. Responses will be studied with and without interactive visual environments. Measures of stability and orientation will be compared and assessed with measures of dynamic visual acuity and with other vestibular function tests. The responses of normal human subjects and of subjects having well-documented pathophysiologies will be characterized. These studies should produce a clearer understanding of normal and abnormal patterns of eye, head and body movement during locomotion and in a wide range of environments. This information will be used to characterize and validate neurovestibular rehabilitative approaches being developed in other Team projects.
CARDIOVASCULAR/NEUROVESTIBULAR SYNERGY PROJECT ABSTRACT:
Visual- and Vestibular-Autonomic Influence on Short-term Cardiovascular Regulatory Mechanisms.
Blunting of the carotid-cardiac baroreflex has been observed during and after spaceflight and prolonged bed rest using the neck barocuff technique (Fritsch et al., 1992; Fritsch-Yelle et al., 1994). Comparable barocuff response changes have recently been reported during yaw axis vestibular stimulation and eye movements (Convertino et al., 1997; Convertino, 1998). It has been suggested that vestibular pathways could play a significant role in changing the orthostatic competence of astronauts and bedridden patients by inhibition of vagal withdrawal and elevation of parasympathetic outflow. However, functional interpretation of neck barocuff data is complicated because this method stimulates only the carotid baroreceptors. Interpretation would be more straightforward if blunting during whole body rotation could be demonstrated using a method like Cardiovascular System Identification (CSI) which provides a measure of overall baroreflex responsiveness. Also, it is important to understand how the vestibular system contributes to cardiovascular control during body tilt, as opposed to yaw rotation. This cannot easily be done using actual body tilt, since the body's non-vestibular gravireceptors (e.g. baroreceptors) are also stimulated. However, we have recently found compelling static tilt and tumbling illusions in a majority of human subjects tested using a virtual reality head mounted display system. We propose to look for baroreflex changes during real and illusory body rotation and tilt using both the neck barocuff and CSI techniques.