By Sindya N. Bhanoo, The New York Times, January 30, 2012
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| A Jumping Spider |
Jumping spiders do
not weave webs. Instead, they jump about and then pounce on their prey. For
this reason, depth perception is very important to their survival.
Now Japanese
researchers have discovered that the spiders use an unusual technique to
estimate how close or far away an object is.
The technique, called image defocus, involves blurring out objects in
the distance while keeping closer ones sharp. Jumping spiders are the only animals
known to use it, but a camera with a good lens demonstrates the same principle
— keeping a person’s face sharp in the foreground while blurring out the trees
in the background.
Takashi Nagata and Mitsumasa Koyanagi of Osaka City University and
their colleagues write about the jumping spiders in the current
issue of Science.
The researchers studied each of the four layers of the retina in one
of the spider’s eyes. They found that green light is never in focus in one of
the layers, and that in another layer it is always in focus.
“So the spider seems to capture a sharp image and a blurry image and
compare the information to estimate the distance of an object,” Dr. Koyanagi
said. Depending on whether a fly, for instance, looks blurry or sharp, the
spider can decide how far to jump.
“It’s
done in real time, so studying this may help develop better computer vision,”
Dr. Koyanagi added.
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