http://www.eurekalert.org/pub_releases/2006-04/qu-ab041806.php
Public release date: 18-Apr-2006
Animal brains 'hard-wired' to recognize predator's foot movements,
Queen's study suggests
'Life detector' could be part of evolutionary old system, say
researchers
KINGSTON, Ont. – The reason people can approach animals in the
wild more easily from a car than by foot may be due to an innate "life
detector" tuned to the visual movements of an approaching predator's
feet, says Queen's University psychologist Niko Troje.
"We believe this visual filter is used to signal the presence of
animals that are propelled by the motion of their feet and the force of
gravity," suggests Dr. Troje, Canada Research Chair in Vision and
Behavioural Sciences.
Conducted with Dr. Cord Westhoff from the Ruhr-Universität Bochum in
Germany, the study was funded by the Canada Foundation for Innovation
and the German Volkswagen Foundation. It will be published on-line
April 18 in the international journal Current Biology.
The researchers suggest this low level locomotion detector is part of
an evolutionary old system that helps animals detect quickly – even on
the periphery of their visual field – whether a potential predator or
prey is nearby. "Research on newly hatched chicks suggests that it
works from very early on in an animal's development," says Dr. Troje.
"It seems like their brains are 'hard wired' for this type of
recognition."
One impetus for starting this research several years ago was a
question by his young daughter, who asked him why she could get so much
closer to wild rabbits in their neighborhood while riding on her
bicycle rather than on foot. "I didn't have an answer for her then.
Now, I think I have one," he says.
Dr. Troje's Motion Capture Laboratory at Queen's uses high speed
cameras to track the three-dimensional trajectories of small reflective
markers attached to the central joints of a person's body. When the
subject moves, these seemingly unstructured white marker dots become
organized into meaningful images, from which observers can determine
the gender, body build, emotional state, and other attributes.
In this study, Dr. Troje's team used "point-light sequence" videos to
display the electronically captured motion of cats, pigeons and humans.
People were tested on whether they could tell the direction of movement
when these cues were changed.
Scrambling the dots didn't create a problem, but when the image was
inverted, observers were unable to say if the animal was moving to the
right or left. The researchers conclude that foot movement is an
independent, important visual cue that another animal is nearby.
"The observation that it is relatively easy to get close to wild
animals in a car, a canoe, or a similar vehicle might be due to the
absence of the typical movement of the feet," says Dr. Troje.
Similarly, the creeping movement of a hunting cat can be interpreted in
terms of disguising the ballistic component in its locomotion, he adds.
"Our finding might also provide an explanation for seemingly irrational
phobias towards animals that don't fit the ballistic movement pattern
of a proposed 'life detector'," he says. "Snakes, insects and spiders,
or birds can generate pathological reactions not observed in response
to 'normal' animals."
###
For a demonstration of the motion capture techniques used in this and
other studies, see the web site of the Queen's Motion Capture
Laboratory at: http://www.bml.psyc.queensu.ca
A PDF copy of the study is available upon request.
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