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Scientific Explanation of the left-right spinning dancer From: Michael Winn
Subject: General
Date/Time 2007-11-13 05:18:45
Remote IP: 66.32.95.77
MessageOne reason I am interested in brain dominance polarity as it may inform the chinese choices of yin and yang sides of the body (yang on left, yin on right), which seem to be opposite of most western descriptions. It raises the question as to whether the polar attributions are universal energy bodies or cultural energy bodies.
m
THE SPINNING DANCER AND THE BRAIN
By Yami McMoots
October 20, 2007
http://greengabbro.net/2007/10/20/the-spinning-dancer-and-the-brain/
This image , originally created by
Nobuyuki Kayahara , is a great scientific
personality test. If you see the dancer spinning clockwise, youıve got
excess spleen qi in your left frontal crockus. This means that youıre a
vibrant personality whose passions are apparent to everyone around you, but
sometimes you are indecisive. If you see her spinning counter-clockwise, the
right ascension of your natal chart lies in your sagittal broab and there
are Fire humours dribbling out your left nostril. You should see a doctor as
soon as possible.
An Australian tabloid recently republished the dancer with a little spiel
about how you can use her spin as an indication of whether you are
right-brained or left-brained. Since then, sheıs propagated all over the
internets, and so has the accompanying spiel.
In contrast to my deeply insightful, completely factitious interpretations
of the left frontal crockus, the tabloidıs claims about ³left brain² and
³right brain² personality types are vastly overblown. But the spinny dancer
is captivating, and because we are watching her with our brains in addition
to our eyeballs, she must surely tell us something about how our brains
work so whatıs actually going on?
As it happens, my fiancé is a professional optical illusion geek. He spends
his time making monkeys play video games, in order to figure out their
visual processing systems. So I made him explain it to me.
This much is true: you process some visual stimuli on the right side of your
brain, and some on the left. You also have two optic nerves, one from the
back of each eyeball. On their way to the brain these nerves meet up in a
location called the optic chiasm. From the optic chiasm, information about
the left side of your field of view, no matter which eye itıs coming from,
is sent to the right hemisphere of your brain to be processed. Information
about the right side of your field of view is sent to the left hemisphere.
Therefore, if you want to see what your right brain makes of the dancer, you
just need to look over to her right and watch her from your peripheral
vision. Looking to her left will show you the left-brained view.
After a little practice, I can get the dancer to switch between clockwise
and counter-clockwise spins - from either side of my visual field. This
means both sides of my brain see both directions of spin just fine. This
effect doesnıt have anything to do with differences in visual processing by
the right and left sides of the brain.
Actually, the spinning dancer is an example of something called bistable
perception. As an object that can be seen in either of two ways, itıs in the
same class of illusion as the Necker cube
and the face-vase
.
Your visual system has evolved to construct a reasonable mental image of the
world with a limited amount of information, and it uses a dizzying array of
assumptions to do so. In the natural world these assumptions are mostly
valid, and thereıs only one right way to interpret any given set of signals.
Artists and sundry neuroscientists, however, can consciously exploit the
assumptions your brain makes about the objects itıs looking at to produce
images with two or more equally valid interpretations.
When presented with stimuli that have two valid, mutually contradictory
interpretations, your brain just picks one. Then, sometimes, it picks the
other. We still donıt understand why this happens, or what role conscious
efforts might play in this shift in perception. Many people are able to make
the dancer shift directions at will, but the strategies Iıve seen almost
always invoke a change of focus - I shift my attention to her feet, or
scroll up and down, others look at her hands or to her side. (Iıve also seen
lots of people talk about staring at her nipples, but none who report that
it helps them see her change directions.)
There is absolutely nothing special about what your brain is doing when it
takes some funny black shapes and turns them into a dancer who spins in both
directions. Bistable stimuli are resolved using the exact same neural
circuitry as everything else, and you can prove it by sticking electrodes
into monkeysı heads (e.g., Grunewald et al., 2002). You could probably prove
it by sticking electrodes into your own head, too, if you felt like it.
Bistable images are useful tools for experiments, because they allow us to
isolate the part of visual processing where the brain is actually making a
decision about how to interpret an image from the parts that are purely
determined by the action at the back of your eyeball.
Bistability is not just a visual phenomenon, either - thereıs an audio
version called the tritone paradox. * If humans had less wimpy olfactory
processing, Iım sure we could figure out some bistable smell illusions, too
- though as far as I know no one has tried to confuse dogs with this
particular technique.
If this explanation hasnıt been technical enough for you, try this review
paper by Parker and Krug:
http://tinyurl.com/2vc4tb
.............
* The way you perceive the tones in the tritone paradox is strongly related
to your native language and the region in which you grew up. Itıs harder to
switch your perception of this paradox than it is to switch with most visual
illusions, but after listening a couple times and paying attention to the
overtones, I could hear the second pair of tones in the other direction.
There are lots of cool audio illusions to play with if you poke around that
site. This one, which ostensibly induces your brain to pick out words
related to things it has been dwelling on lately, is depressing -- I default
to hearing the words ³no way² repeated over and over. But if I move my
speakers around a little I also start to hear ³burp², ³rainbow², ³wanker²,
and the name of the guy in the office next door. I think Iıll stick to
interpreting my dreams instead.
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