During spaceflight, astronauts are exposed to zero-gravity and also to large G-forces during liftoff and landing. These unusual conditions can lead to false perceptions of body orientation and self-movement. To better understand these experiences, NSBRI Postdoctoral Fellow Dr. Paul MacNeilage is developing a model for spatial orientation perception that can be used to predict and investigate situations where spatial disorientation is likely to occur. The model uses sensory estimates from the visual and vestibular systems to generate combined estimates of orientation, linear velocity and angular velocity. He will then test predictions of the model in a series of experiments designed to measure performance in a variety of conditions. The results of these experiments could be applied to the development of countermeasures including better cockpit display technology, improved motion simulations, novel pilot training techniques and crew-screening procedures.
Psychophysics and Modeling of Spatial Orientation Perception (Postdoctoral Fellowship)
Paul MacNeilage, Ph.D.
- Develop a comprehensive Bayesian model for spatial orientation perception. In order to develop the best possible model, we conducted a thorough review of existing spatial orientation models (MacNeilage et al 2008). We focused on statistically optimal models of spatial orientation that are dynamic, meaning that the model input and output are continuous and vary over time. We concluded that the particle filter technique is best suited to modeling perception of spatial orientation because it is statistically optimal, the architecture is distributed rather than assuming particular feedback circuits, and most importantly, it is capable of implementing the non-linear system dynamics that are required for spatial orientation computations. Our review has provided key insights that will guide future modeling efforts. We have discussed these issues in some detail with other NSBRI investigators developing online systems that can predict spatial disorientation and alert crew members in situations when it is likely to occur (Project Title: Modeling and Mitigating Spatial Disorientation in Low-Gravity Environments; Principal Investigator: Ronald L. Small).
- Measure visual and vestibular thresholds for detecting and discriminating spatial orientation stimuli. We conducted three such experiments using a motion simulator with attached stereo visual display. We used a two-alternative-forced-choice procedure because this method minimizes potential sources of response noise and bias. Also, because all data were collected using a common method and apparatus, it is possible to make interesting comparisons across conditions.
In a second experiment, we investigated the question of whether or not vestibular cues to linear and angular self-motion interact during rotation about an Earth-vertical axis. Linear and angular self-motion is signaled by the otoliths and canals, respectively. During rotation about an Earth-horizontal axis (i.e. tilt), these signals must interact so that the brain correctly interprets the change in the otolith signal as due to a change in the direction of gravity. In contrast, we found no evidence of canal-otolith interaction during rotation about an Earth-vertical axis. Thresholds for detecting linear acceleration were not influenced by the speed of angular motion.
In a third experiment, we investigated whether or not vestibular cues to linear self-motion facilitate the detection of visual object motion during self-motion. Linear self-motion gives rise to a distinctive globally consistent pattern of motion on the retina known as optic flow. Independently moving objects in the scene will generate visual motion signals that deviate from the global pattern. Thus, observers must parse the optic flow in order to judge object motion during self-motion. We found that thresholds for discriminating object motion in optic flow patterns were reduced when vestibular signals consistent with the linear self-motion depicted by the optic flow were presented simultaneously. In other words, vestibular signals facilitate optic flow parsing.
The research described above contributes to a better understanding of spatial orientation in general. The modeling review provides unique insights that will be valuable for developing and evaluating models to predict and investigate situations where spatial disorientation is likely to occur. The results of the experiments provide a better understanding of visual and vestibular perception of spatial orientation stimuli which may be applied to the development of countermeasures like better cockpit display technology and improved motion simulations. The psychophysical methods employed could be used to develop novel techniques for crew training and evaluation.
The psychophysical measurements we are making also contribute to a better general understanding of spatial orientation perception. The methodologies we have developed for these experiments could be used to assess performance of spatial orientation tasks by astronauts. They could also be used to assess the performance of aircraft pilots or patients with visual or vestibular deficits.