Visual cues help us understand body motion

Toronto: Humans are so good at perceiving others that even a few dots on a screen representing the major joints of a body are enough to retrieve all the information we need -- as long as they move.

This process is called biological motion perception, but what role does the visual system play in that process? Does it use it only to connect the dots to create a coherent, or "global," structure?

"Our visual system is tuned towards perceiving other people. We spend so much time doing that -- seeing who they are, what they are doing, what they intend to do," says psychology professor Nikolaus F. Troje of Queen`s University in Kingston, Ontario.

Troje and colleagues -- Masahiro Hirai and Daniel R. Saunders at Queen`s, and Dorita H.F. Chang, now at the University of Birmingham, UK -- examined this question, reports the journal Psychological Science.

They presented their participants with computer-generated stimuli showing 11 light points representing the shoulder, hip, elbows, wrists, knees, and ankles of a person walking, as on a treadmill, according to a Queen`s statement.

After a two-second display, the observers had to indicate which direction they believed the walker was facing. This is an easy task, and the participants performed it almost without fail -- even though the point-light walker was masked with 100 randomly placed additional dots.

But they were also able to do it if the structure of the body was entirely disrupted by randomly scrambling the 11 dots.

"The local motion of individual dots contained enough information about the walker`s facing direction," says Troje.


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