Spatial Orientation and Navigation in Microgravity

Abstract

This chapter summarizes the spatial disorientation problems and navigation difficulties described by astronauts and cosmonauts, and relates them to research findings on orientation and navigation in humans and animals. Spacecraft crew are uniquely free to float in any relative orientation with respect to the cabin, and experience no vestibular and haptic cues that directly indicate the direction of "down". They frequently traverse areas with inconsistently aligned visual vertical cues. As a result, most experience "Visual Reorientation Illusions" (VRIs) where the spacecraft floors, walls and ceiling surfaces exchange subjective identities. The illusion apparently results from a sudden reorientation of the observer's allocentric reference frame. Normally this frame realigns to local interior surfaces, but in some cases it can jump to the Earth beyond, as with "Inversion Illusions" and EVA height vertigo. These perceptual illusions make it difficult for crew to maintain a veridical perception of orientation and place within the spacecraft, make them more reliant upon landmark and route strategies for 3D navigation, and can trigger space motion sickness. This chapter distinguishes VRIs and Inversion Illusions, based on firsthand descriptions from Vostok, Apollo, Skylab, Mir, Shuttle and International Space Station crew. Theories on human "gravireceptor" and "idiotropic" biases, visual "frame" and "polarity" cues, top-down processing effects on object orientation perception, mental rotation and "direction vertigo" are discussed and related to animal experiments on limbic head direction and place cell responses. It is argued that the exchange in perceived surface identity characteristic of human VRIs is caused by a reorientation of the unseen allocentric navigation plane used by CNS mechanisms coding place and direction, as evidenced in the animal models. Human VRI susceptibility continues even on long flights, perhaps because our orientation and navigation mechanisms evolved to principally support 2D navigation. 2 Chapter Error! No text of specified style in document.

Directional learning, but no spatial mapping by rats performing a navigational task in an inverted orientation

“…This finding is consistent with other studies showing an independence of these two simple orientation strategies from the HD signal (Golob, Stackman, Wong, & Taube, 2001). Interestingly, our findings are consistent with observations in 0-g conditions where astronauts frequently have great difficulty forming a three dimensional representation of their spatial environment and often report a profound sense of disorientation (Oman, 2007). Under 0-g conditions, there is an alteration in the normal otolith signal experienced by astronauts and this unfamiliar situation (in an unknown way) impedes the astronaut's ability to form an accurate representation of their spatial environment.…”

The Head-Direction Signal Is Critical for Navigation Requiring a Cognitive Map but Not for Learning a Spatial Habit

“…Our findings may account for why astronauts have difficulty with spatial relationships in space, particularly with 3D relationships, and frequently become disoriented [16]. If astronauts also have disrupted HD cell activity when in 0-g, this situation may explain their navigational impairments and their subsequent reliance on other strategies for solving spatial problems - similar to the rats in our study.…”

Vestibular contribution to three-dimensional dynamic (allocentric) and two-dimensional static (egocentric) spatial memory

“…Astronauts' reports support this view: when working in their spaceship in microgravity they experienced ''visual reorientation illusions'' [4]. Contrary to the patients with vestibular loss, the astronauts had a functioning vestibular system, but no static stimulation of the otoliths.…”

“…Contrary to the patients with vestibular loss, the astronauts had a functioning vestibular system, but no static stimulation of the otoliths. To know where to look, grasp, or move about in the cabin, astronauts must visually recognize landmarks that allow them to infer their self-orientation with respect to surrounding objects, since the notion of a (vestibular) ''gravitational down'' is meaningless [4]. Likewise neurological patients with a spatial hemineglect, which involves the vestibular cortex, have both object-based allocentric and body-centered egocentric impairment of spatial awareness [5].…”