Long-term exposure to microgravity impacts astronauts’ perception of upright

Researchers at York University’s Centre for Vision Research (CVR) have discovered that astronauts who experience extended periods of microgravity experience long-term disturbances in their perception of upright.

The study “The effect of long-term exposure to microgravity on the perception of upright” appears this month in the Nature Partner Journal: Microgravity. The project investigates how astronauts understand which way is up while in microgravity, and how this changes when they return to Earth.

Astronauts on the International Space Station take part in the experiments designed by the BISE Project researchers

The results represent a major finding that will have an impact on how future extended space flights are planned and implemented.

Laurence Harris

Led by Faculty of Health Professor Laurence Harris, with co-investigator Professor Michael Jenkin of the Lassonde School of Engineering, the study of astronauts’ perception of upright is the culmination of the Bodies in the Space Environment (BISE) experiment, a multi-year project that was conducted in collaboration with the International Space Station (ISS) and sponsored by the Canadian Space Agency (CSA).

“On Earth, we use visual, body and gravity information to determine our sense of orientation, which is critical to many perceptual tasks including reading, recognizing faces, and, particularly important in a space environment, navigating around and interacting with the environment,” says Harris.

On the ISS, gravity is not available and astronauts must adjust how they determine which way is up. Harris and his team measured how seven astronauts, who spent 168 days on average on the ISS, perceived their orientation before, during and after flight, and compared these results to those from a control group on earth. Remarkably, no changes were observed in the astronaut’s perception of the direction of up during their missions.

Experiencing long periods of microgravity can have a lasting impact on an astronaut’s perception of what is up

“This indicates an impressive adaptability to a microgravity environment in which the dependence on visual cues to orientation is rapidly reduced to maintain its original, on-Earth relationship to the body,” adds Harris.

The researchers discovered that a reduced emphasis on vision persisted for up to four months after the astronauts returned to Earth indicating that readjusting to gravity may take longer than previously thought.

“The implications of this disturbance to the perception of upright could have ramifications for future missions such as those planned for Mars,” says Jenkin. The effects of long-term exposure to zero gravity could have an adverse effect the perception required to safely land on a planet.

“The disturbance in perception could impact how quickly the crew is able to function in the new gravity environment, which is critical,” says Jenkin, “given that no ground team will be available to help the astronauts readjust.”

The CVR Mission badge

Knowing “which way is up” is fundamental to our survival. On Earth, it is crucial to know where to put your feet to support your body and how to adjust to threats to this stability. In space, knowing which way is up is not needed for balance in the same way but is crucial for tasks such as knowing whether a toggle switch is in the on or off position and which way to go to get to the emergency hatch.

The findings could help with the development of countermeasures to avoid perceptual mistakes during space travel, and contribute to facilitating safer, long-duration journeys without gravity.

In addition to Harris and Jenkin, co-investigators on the study included CVR researchers Heather Jenkin, James E. Zacher and the late Richard Dyde.

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