We all have an implicit knowledge of Newtonian physics, according to a study of astronauts playing ball games in space.
Balls were thrown down from above the astronauts鈥� heads, first on Earth and then later in space. In zero gravity, they started moving their arms to catch the ball too soon.
The mistake in timing was only very slight 鈥� but it reveals that people take gravity into account when judging an object鈥檚 鈥渢ime to impact鈥�, says Joseph McIntyre at the European Laboratory for the Neuroscience of Action in Paris, France.
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This contradicts a classic theory that retinal information alone is sufficient for a person鈥檚 brain to coordinate their movement in response to a falling object.
鈥淭he differences we saw were small. You might imagine that in a very critical situation in space they would be important. But for most everyday tasks, you wouldn鈥檛 predict any problems,鈥� McIntyre told New 杏吧原创.
鈥淲e did this study more to understand how the brain works, and less to try to understand what might happen to astronauts in space.鈥�
The space study was carried out in the shuttle鈥檚 Neurolab. The astronauts were tested three times during their two-week mission. Balls were projected down at one of three randomly chosen initial speeds, from a height of 1.6 metres above their heads.
鈥淥n Earth, catching responses were well synchronised with the arrival of the ball,鈥� the team write in the journal Nature Neuroscience. But not so in space.
The astronauts started rotating their forearm upward to meet the ball about 400 milliseconds earlier than they did on the ground. They also started stiffening their arms about 50 milliseconds too early.
鈥淚f you are anticipating gravity and it isn鈥檛 there, you will be able to partly correct for that,鈥� McIntyre says. This is because the brain constantly updates its model of the motion of the falling balls.
鈥淏ut there will be small differences in timing 鈥� and that鈥檚 exactly what we found. The differences we saw in flight are consistent with the idea that the brain is anticipating acceleration due to gravity,鈥� he says.
McIntyre鈥檚 team did find that by the end of the shuttle mission, the astronauts had started to adapt.
鈥淓ven on the 15th day of the mission, they were still anticipating gravity, but the effect was starting to diminish,鈥� McIntyre says.
Anecdotal evidence suggests that they had much more trouble catching balls when they first returned to Earth, than in their first days in space.
鈥淚f you anticipate too early, you鈥檒l probably still catch the ball. But if your responses are a little bit late 鈥� as it sounds like they were when they came back 鈥� that鈥檚 more catastrophic.鈥�
More at: Nature Neuroscience (vol 4, p 693)