April 13, 2024

Astronauts are surprisingly good at judging gravity-free distances

Astronauts have an incredible talent for judging distances in the weightlessness of space, according to new research published in the journal npj microgravity. The findings revealed that astronauts have a surprisingly accurate ability to estimate distances traveled in a microgravity environment, such as aboard the International Space Station (ISS).

The research was a collaborative effort led by the University of York in partnership with the Canadian Space Agency, NASA and other international space agencies. But why embark on such a study? The adventure in space presents unique challenges to astronauts, including the absence of gravity.

This lack of gravity affects several bodily functions and senses, including how we perceive movement and orient ourselves in space. Given the critical nature of precise movement and navigation in spacecraft or while performing spacewalks, understanding and improving astronauts’ spatial awareness in microgravity is critical.

“It has been repeatedly demonstrated that the perception of gravity influences perceptual ability. The most profound way to observe the influence of gravity is to eliminate it, which is why we took our investigation to space,” said study author Laurence Harris, professor of psychology and director of the Multisensory Integration Laboratory.

“We have had a constant presence in space for nearly a quarter of a century and with space efforts only increasing as we plan to return to the Moon and beyond, responding to health and safety concerns becomes increasingly important. Based on our findings, it appears that humans are surprisingly capable of adequately compensating for the lack of a normal Earth environment using vision.”

The research focused on two main groups: astronauts who would perform the tasks both on Earth and in the microgravity environment of the ISS, and a control group who underwent similar tests only on Earth. The group of astronauts consisted of 15 individuals (8 women and 7 men), although not all of them completed the study due to various reasons such as spaceflight delays or the inability to complete the second testing session within a specific time frame.

There were 12 astronauts left (6 men and 6 women) who fully completed all aspects of the testing protocol. The control group initially consisted of 22 participants, 20 of whom completed the study due to abandonment caused by nausea in some cases.

The researchers used virtual reality (VR) technology to simulate a three-dimensional corridor, which served as the main setting for the experiments. The hallway was designed with points of light on the walls to create an optical flow, mimicking the visual cues one would experience when moving through the space.

The experimental procedure was carefully designed to assess participants’ ability to estimate distances in a simulated environment. Participants viewed a target at various distances in the virtual hallway and were asked to estimate the egocentric distance to the target. After making the estimate, they signaled the start of the test, and the target disappeared, replaced by optical flow simulating movement toward the target location.

Participants then indicated when they felt they had reached the target position. This process was repeated across multiple trials and distances without providing any performance feedback to ensure that learning effects did not influence results.

The astronauts underwent testing in five different phases: before spaceflight, early and late during their mission to the ISS, and early and late after their return to Earth. While on Earth, tests were carried out with astronauts in sitting and supine postures (lying face up) to simulate different orientations in relation to gravity.

A key finding from the research was the significant role that visual cues, or optical flow, play in astronauts’ perception of motion and distance in space. Optical flow refers to the pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer and the scene. In the weightlessness of space, where gravity-related vestibular cues are unavailable, astronauts appear to rely more on these visual cues to judge distance traveled.

The study also found that posture affects the perception of distance on Earth. Specifically, when participants were in a supine position (lying face up), they tended to estimate distances as being shorter compared to when they were sitting upright. This finding was consistent with the hypothesis that the absence of typical gravitational cues may lead to a greater reliance on visual information to estimate distances.

Furthermore, the results showed no significant difference in the astronauts’ performance before and after spaceflight. This indicates that the microgravity experience does not negatively affect astronauts’ ability to perceive distances upon returning to Earth. It’s an encouraging sign for long-duration space missions, suggesting that astronauts can quickly readjust to Earth’s gravity without lasting impairments in spatial perception.

However, the study has its limitations, including the small sample size and exclusion of data from participants who did not complete all testing sessions. Additionally, the astronauts were not tested immediately upon arriving at the ISS, meaning the initial phase of adapting to microgravity was not captured.

The researchers call for more studies to explore these findings, especially to understand the long-term effects of spaceflight on spatial orientation and how this knowledge can benefit people with balance disorders on Earth.

The study, “The effects of long-term exposure to microgravity and body orientation relative to gravity on perceived distance traveled,” was authored by Björn Jörges, Nils Bury, Meaghan McManus, Ambika Bansal, Robert S. Allison, Michael Jenkins and Laurence R. Harris.

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