First documented by Aristotle, Motion |
Scientists
have come up with new insight into the brain processes that cause the
optical illusion in the video below. Focus your eyes directly on the “X”
in the center of the image.
The
yellow jacket (Rocky, the mascot of the University of Rochester)
appears to be expanding. But he is not. He is staying still. We simply
think he is growing because our brains have adapted to the inward motion
of the background and that has become our new status quo. Similar
situations arise constantly in our day-to-day lives – jump off a moving
treadmill and everything around you seems to be in motion for a moment.
This
age-old illusion, first documented by Aristotle, is called the Motion
Aftereffect by today’s scientists. Why does it happen, though? Is it
because we are consciously aware that the background is moving in one
direction, causing our brains to shift their frame of reference so that
we can ignore this motion? Or is it an automatic, subconscious response?
Davis
Glasser, a doctoral student in the University of Rochester’s Department
of Brain and Cognitive Sciences thinks he has found the answer. The
results of a study done by Glasser, along with his advisor, Professor
Duje Tadin, and colleagues James Tsui and Christopher Pack of the
Montreal Neurological Institute, will be published this week in the
journal Proceedings of the National Academy of Sciences (PNAS).
In
their paper, the scientists show that humans experience the Motion
Aftereffect even if the motion that they see in the background is so
brief that they can’t even tell whether it is heading to the right or
the left.
Even
when shown a video of a pattern that is moving for only 1/40 of a
second (25 milliseconds) – so short that the direction it is moving
cannot be consciously distinguished – a subject’s brain automatically
adjusts. If the subject is then shown a stationary object, it will
appear to him as though it is moving in the opposite direction of the
background motion. In recordings from a motion center in the brain
called cortical area MT, the researchers found neurons that, following a
brief exposure to motion, respond to stationary objects as if they are
actually moving. It is these neurons that the researchers think are
responsible for the illusory motion of stationary objects that people
see during the Motion Aftereffect.
This
discovery reveals that the Motion Aftereffect illusion is not just a
compelling visual oddity: It is caused by neural processes that happen
essentially every time we see moving objects. The next phase of the
group’s study will attempt to find out whether this rapid motion
adaptation serves a beneficial purpose – in other words, does this rapid
adaptation actually improve your ability to estimate the speed and
direction of relevant moving objects, such as a baseball flying toward
you.
