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Psychophysics and Modeling of Spatial Orientation Perception (Postdoctoral Fellowship)

Principal Investigator:
Paul MacNeilage, Ph.D.

Washington University

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.

NASA Taskbook Entry

Technical Summary

Spatial orientation is achieved by integrating sensory information from different modalities in order to estimate both body orientation and self-motion. Multiple sources of relevant sensory information are often available, so the question becomes, how should the nervous system combine them? If the goal is to achieve the single most probable combined estimate, then the rule is simple; each information source should be weighted based on its relative reliability. This kind of statistically optimal combination rule is known as Bayesian estimation, and it has been shown to accurately characterize perception in a variety of situations.

Research Aims

  1. 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).

  2. 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.
The first experiment investigated perception of heading, which is the direction of self-motion. Heading perception is fundamental to effective navigation and vehicle guidance, so it is important to understand the factors that influence the precision of visual and vestibular heading estimates. We measured discrimination thresholds for heading azimuth and elevation in visual-only and vestibular-only conditions with observers oriented upright and side-down relative to gravity. Visual thresholds were significantly lower than vestibular and upright thresholds were generally lower than side-down. Vestibular results revealed that observers are better at discriminating head-centric azimuth than elevation, regardless of body orientation. In other words, sensitivity to heading depends more upon the direction of self-motion relative to the head, than relative to gravity. We conducted two follow-up experiments using the same subjects. We found that performance on the three tasks was correlated and determined that the asymmetric vestibular sensitivity to heading stems from an underlying difference in sensitivity to linear acceleration along the interaural and dorsoventral axes of the head.

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.

Earth Applications

Spatial orientation allows astronauts to pilot the space shuttle and navigate their way around the inside of the International Space Station. It also allows people here on Earth to get where they are going and avoid collisions while driving a car or riding a bike. Perception of spatial orientation is essential for mobile organisms to navigate effectively within the environment. Without perception of spatial orientation, we are literally lost. By successfully modeling perception of spatial orientation, we can predict when spatial disorientation is most likely to occur. This will help astronauts avoid potentially disorienting and hazardous situations in space. It could also help avoid spatial disorientation here on Earth. For example, it could lead to the development of technology that helps drivers avoid disorientation and accidents on the road.

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.

This project's funding ended in 2009