Why does depth perception change during spaceflight? I’ve got answers!

In my April 13 blog entry I wrote about an experiment known as Reversible Figures that was performed by astronauts aboard the International Space Station. I also asked your thoughts on how depth perception might change during spaceflight. The results of this experiment have recently been published so I am now at liberty to provide the answer.

An ISS astronaut wearing a head-mounted display and holding a finger mouse in his hand performs the Reversible Figures experiment while free-floating.

An ISS astronaut wearing a head-mounted display and holding a finger mouse in his hand performs the Reversible Figures experiment while free-floating.

You recall that the objective of the Reversible Figures experiment was to learn whether the perception of illusory depth was altered in astronauts during long spaceflights. To investigate this, reversible figures (simple two-dimensional drawings of objects that we perceive in three-dimensions) were repeatedly viewed by astronaut subjects before, during and after spaceflight.


A sample of reversible figures viewed by ISS astronauts (Necker’s Cube is one the left).

Reversible figures such as those shown above can be interpreted three-dimensionally in two different ways by the brain. The findings from the experiment showed that on Earth the astronauts predominantly (i.e. about 70% of the time) viewed each of the above four figures one way. Most of the time, for instance, they perceived Necker’s Cube as though it was a box resting on a surface (i.e. as though viewed from above). When looking at the drawing of the chair, astronauts saw a chair with the seat pointing towards them (i.e. as though viewed from above) more often than with the seat pointing away.

In space, the results showed that this 70:30 asymmetry progressively decreased as the flight progressed. After several months in space, the astronauts perceived both depth interpretations equally. About 50% of the time Necker’s Cube was perceived as though resting on a surface and about 50% as though hanging from the ceiling.

Back on Earth, the 70:30 asymmetry quickly returned.

This change in depth perception during spaceflight is attributed to the lack of the gravitational reference for interpreting perspective depth cues. This result is relevant for space exploration because changes in 3D visual perception may influence an astronaut’s ability to accurately perform tasks such as grasping objects, operating robotic arms or controlling spacecraft.

The results of the Reversible Figures experiment have now been published in an online journal. You can click on this link to read the nitty-gritty details.

Or even better, you can watch a short video documentary that nicely summarizes the experiment. The documentary was produced by the students of Robert Thirsk High School in Calgary – they did a great job. In fact, their video was accepted as an entry in the Youth-By-Youth Cinema Competition at the Calgary International Film Festival. At last Saturday’s screening at the TELUS Spark Centre, their film received the “Special Local Narrative Award”. Well done, RTHS!

You can watch the ‘Reversible Figures Experiment’ online by clicking on this YouTube link http://youtu.be/sKtTFOG3PaQ


Proud cinematographers of the Robert Thirsk High School film club

In my April 13 blog entry, I also asked readers how the astronauts’ perception of 3D reversible figures might’ve been altered during spaceflight. Alina Kunitskaya’s response was quite close to the actual experiment results so I provided her with a signed photo. Well done, Alina. You’re a budding neurophysiologist!


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