Aim 1 was to examine the effects of stimulus frequency (0.01 - 0.6 Hz ) on adaptive changes in eye movements, motion perception and cognition during combined tilt and translation motion profiles. We hypothesized that adaptation of otolith-mediated responses will be greatest in the mid-frequency range where there is a tilt-translation crossover. Our findings emphasized differences in the neural processing to distinguish tilt and translation between eye movements and motion perception. Specifically, during dynamic linear stimuli in the absence of canal and visual input, a change in stimulus frequency alone elicits similar changes in the amplitude of both self motion perception and eye movements. However, in contrast to the eye movements, the phase of both perceived tilt and translation motion is not altered by stimulus frequency over this limited range. Our findings also suggest that the frequency at which there was a crossover of perceived tilt and translation gains appeared to vary across different motion paradigms (e.g., near 0.3 Hz during off-vertical axis rotation and near 0.15 Hz during sled translation).

Adaptation experiments conducted below this cross-over frequency using the 'vision-aligned' paradigm have resulted in modest changes to both eye movements and motion perception, consistent with our first hypothesis. Adaptation experiments conducted around this cross-over frequency range using the 'GIF-aligned' paradigm demonstrated a significant effect of stimulus frequency on both motion sickness and spatial cognitive performance.

Aim 2 was to examine changes in control errors during a closed-loop nulling task before and after tilt-translation adaptation. We hypothesized that the ability to control tilt orientation will be compromised following tilt-translation adaptation, with increased control errors corresponding to changes in self-motion perception. Roll tilt nulling was implemented using the both step and pseudorandom stimuli in darkness. Our findings suggest that these types of manual control tasks are sensitive to underlying changes in sensorimotor physiology, and specifically to changes in the brain's interpretation of linear acceleration stimuli.

Aim 3 was to evaluate how a tactile prosthesis might improve control performance. A simple 4 electromechanical tactor system was developed that provided 6 threshold levels of orientation information. We also examined the influence of vibrotactile feedback during computerized posturography. A significant reduction in RMS error (p<0.05) was observed using this simple tactile prosthesis, both during manual and balance control tasks. These results are promising in that a fairly simple device with as few as 4 tactors may prove useful to significantly improve landing performance.

Aim 4 was to examine how spatial awareness is impaired with changing gravitational cues during parabolic flight, and the extent to which vibrotactile feedback of orientation can be used to help improve spatial awareness. Our findings suggest that tactile cueing may improve navigation in operational environments, such as extravehicular activities on a lunar surface. This type of sensory feedback may also prove beneficial as a navigation aid in patient populations, providing non-visual, non-auditory feedback of orientation or desired direction heading.

Our first specific aim is to examine the effects of stimulus frequency and different patterns of inertial sensory cues on adaptive changes in eye movements and motion perception during combined tilt and translation motion profiles. Our first hypothesis is that adaptation of otolith-mediated eye movement and perceptual responses will be greatest in the mid-frequency range where there is a crossover of tilt and translation otolith-mediated responses. We are testing this hypothesis by exposing subjects to various combinations of tilt and translation motion profiles over the frequency range from 0.01 Hz to 0.6 Hz. Changes in eye movement and perceptual tilt responses are determined by comparing pre- and post-adaptation runs performed in darkness.

Baseline eye movements and motion perception elicited during various combinations of tilt and translation stimuli have compared across multiple acceleration platforms. Constant velocity off-vertical axis rotation (OVAR) provides a continually changing head and body orientation relative to gravity where the equivalent linear acceleration is a function of tilt angle and the frequency is a function of rotation rate. Variable radius centrifugation (VRC) is another technique that allows low frequency linear acceleration by combining the centripetal acceleration and sled acceleration to achieve the desired resultant linear acceleration amplitude. Tilting about an Earth horizontal axis and translation along a linear track or sled are the final two motion paradigms that have been used to characterize how the brain interprets linear acceleration at different frequencies. The key findings of these studies have been that the neural processing to distinguish tilt and translation differs between eye movements and motion perception. These findings have an important impact in assessing tilt-translation disturbances following space flight or the adaptation experiments that are planned for the final year.

Adaptive changes using a ‘vision aligned’ paradigm have been conducted by exposing subjects to matching tilt self motion with conflicting visual surround translation. The optimal phase relationship between body tilt and scene translation was examined at 0.1 Hz in the pitch plane using JSC’s Tilt-Translation Device (TTD, designed to recreate post-flight orientation disturbances. This study demonstrated that a 180 deg phase relationship should be employed during subsequent studies, although asymmetric stimuli may provide the most robust changes in the pitch plane. Similar studies in the roll plane are in progress at Legacy Health System in Portland OR using a hydraulic powered tilt chair with a chair-mounted horizontal optokinetic stimulus. Finally, a new Tilt-Translation Sled was recently installed at JSC to implement a ‘GIF aligned’ paradigm in which the chair will tilt within an enclosure that will simultaneously translate, resulting in a mismatch in which the canals and vision signal tilt while otoliths do not.

Our second specific aim is to examine changes in control errors during a closed-loop nulling task before and after tilt-translation adaptation. We predict the ability to control tilt orientation will be compromised following tilt-translation adaptation, with increased control errors corresponding to changes in self-motion perception. Roll tilt nulling was implemented using the hydraulic tilt chair with both step and pseudorandom stimuli in darkness. Future studies are planned using tilt nulling with a constantly moving visual scene to simulate the brown-out conditions that were encountered during the initial lunar landings.

Our third specific aim is to evaluate how a tactile prosthesis might improve control performance. A simple 4 electromechanical tactor system was developed that provided 6 threshold levels of orientation information. We also examined the influence of vibrotactile feedback during computerized posturography. A significant reduction in RMS error (p<0.05) was observed using this simple tactile prosthesis, both during manual and balance control tasks. These results are promising in that a fairly simple device with as few as 4 tactors may prove useful to significantly improve landing performance. Both studies demonstrate how a tactile prosthesis can be optimized with feed-forward projections using velocity information.

During the final year, experiments integrating all three specific aims will be conducted using the Tilt-Translation sled at JSC to provide the ‘GIF-aligned’ paradigm and the hydraulic chair at Legacy to provide the ‘visual-aligned’ paradigm. The results of this study will contribute to the refinement of the tactile prosthesis to improve spatial orientation and navigation on different acceleration platforms, including landing systems used for return to Earth after long duration space travel or landing systems used during space exploration missions.

Initial adaptation experiments have been conducted using a visual-aligned paradigm in which passive tilt is coupled with moving scene translation. The initial study performed with JSC’s Tilt Translation Device in the pitch plane demonstrated that the visual scene otion with 180 deg phase results in a significantly reduced perceived tilt and increase linear vection and vergence eye movements compared to pre-exposure tilt stimuli in darkness (O’Sullivan et al, 2006). A second study is in progress using roll tilt stimuli coupled with a horizontally moving visual scene. Another study was implemented this past year to optimize the use of passive dynamic visual acuity as a dependent measure of visual performance changes (Wood et al, 2007).

Our second specific aim has focused on changes in control errors during a closed-loop nulling task before and after tilt-translation adaptation. Roll tilt nulling demonstrated that control performance was compromised by low-frequency bias during pseudorandom stimuli in darkness (Wood et al., 2006). Preliminary findings suggest that these types of manual control task are sensitive to underlying changes in sensorimotor physiology. A follow-up study is examining the influence of low frequency visual scene motion to simulate the effect of brown-out conditions reported during lunar landings.

Our third specific aim is to evaluate how a tactile prosthesis might improve control performance. A simple 4 electromechanical tactor system was developed that provided 6 threshold levels of orientation information. A significant reduction in RMS error (p<0.05) was observed using this simple tactile prosthesis, both during manual (Rupert et al., 2006) and balance control tasks (Wood et al., 2006). These results are promising in that a fairly simple device with as few as 4 tactors may prove useful to significantly improve landing performance.

Our first specific aim is to examine the effects of stimulus frequency and different patterns of inertial sensory cues on adaptive changes in eye movements and motion perception during combined tilt and translation motion profiles. Our first hypothesis is that adaptation of otolith-mediated eye movement and perceptual responses will be greatest in the mid-frequency range where there is a crossover of tilt and translation otolith-mediated responses. We are testing this hypothesis by exposing subjects to various combinations of tilt and translation motion profiles over the frequency range from 0.1 Hz to 0.6 Hz. Changes in eye movement and perceptual tilt responses are determined by comparing pre- and post-adaptation runs performed in darkness. During first phase of this grant, we have examined adaptive changes using a ‘vision aligned’ paradigm with JSC’s Preflight Adaptation Training laboratory’s Tilt-Translation Device (TTD). This device was designed to recreate post-flight orientation disturbances by exposing subjects to matching tilt self motion with conflicting visual surround translation. While linear vection is robust during the vision aligned paradigm at 0.1 Hz, the post-adaptive changes are relatively small as predicted at these lower stimulus frequencies. We also conducted control studies for the simultaneous measurement of tilt and translation motion perception using constant velocity Off-Vertical Axis Rotation. Perceived motion was evaluated using verbal reports, a multi-axis joystick, and a simple push-button task indicating nose-up orientation. These studies are important to refine methodology to be used in subsequent adaptation experiments planned for the coming year. More importantly, these studies emphasize differences in the neural processing to distinguish tilt and translation linear acceleration stimuli between eye movements and motion perception.

Our second specific aim is to examine changes in control errors during a closed-loop nulling task before and after tilt-translation adaptation. We predict the ability to control tilt orientation will be compromised following tilt-translation adaptation, with increased control errors corresponding to changes in self-motion perception. During this past year, we reported results of control nulling experiments during roll-tilt step and pseudorandom profiles. This experiment also allowed us to initiate our third specific aim to evaluate how a tactile prosthesis might improve control performance. A simple 4 electromechanical tactor system was developed that provided 6 threshold levels of orientation information. We also examined the influence of vibrotactile feedback during computerized posturography. A significant reduction in RMS error (p<0.05) was observed using this simple tactile prosthesis, both during manual and balance control tasks. These results are promising in that a fairly simple device with as few as 4 tactors may prove useful to significantly improve landing performance. Both studies demonstrate how a tactile prosthesis can be optimized with feed-forward projections using velocity information.

The major effort in the first phase of the project was to design and develop a device to incorporate the ‘GIF aligned’ paradigm in which the chair will tilt within an enclosure that will simultaneously translate so that the resultant gravitoinertial force (GIF) vector remains aligned with the longitudinal body axis. This paradigm will result in a mismatch in which the canals and vision signal tilt while the otoliths do not. The Naval Aerospace Medical Research Laboratory in Pensacola has designed an air bearing track with dual ironless linear motors to provide the translational motion. A dual-wheel friction drive provides tilt chair motion up to 45 deg from vertical inside an 8 feet cube enclosure. During this next year, this device will be used to examine the effects of stimulus frequency on adaptive changes in otolith ocular reflexes, motion perception and closed-loop nulling performance. We will also continue to refine the simple tactile prosthesis, optimizing feed-forward information from velocity to improve control performance. The results of this study will contribute to the refinement of the tactile prosthesis to improve spatial orientation and navigation on different acceleration platforms, including landing systems used for return to Earth after long duration space travel or landing systems used during space exploration missions.

Control studies were conducted to evaluate the simultaneous measurement of tilt and translation motion perception using constant velocity Off-Vertical Axis Rotation. Perceived motion was evaluated using verbal reports, a multi-axis joystick, and a simple push-button task indicating nose-up orientation. These studies are important to refine methodology to be used in subsequent adaptation experiments planned for the coming year. These studies lead to one submitted manuscript, and another in preparation.

In support of Specific Aim 2, results of the roll-tilt nulling experiments completed in year 1 were summarized and presented at two scientific conferences. In support of Specific Aim 3, this study demonstrated how feed-forward information from velocity improved control performance. Also in support of Specific Aim 3, the results of a tactor study during computerized posturography were summarized and presented at another conference. This study was important to expand the application of the tactor system to balance disruption following space flight. Two manuscripts are in preparation from these tactor studies.

The Naval Aerospace Medical Research Laboratory (NAMRL) Engineering Services in Pensacola has completed the device to provide the ‘GIF aligned (gravitoinertial force) paradigm. The progress on this development was delayed due to servo problems with the linear track. Both encoder and drive systems were replaced for the linear track to resolve this issue, and now the device will be operational for the initial studies at the beginning of the next project year. Due to the reduced funding, the initial studies will be conducted at Pensacola to facilitate any modifications needed prior to its relocation to NASA.