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There is a difference between what is called persistence of vision which
is a physiological phenomenon, and apparent motion, which is a
psychophysical phenomenon. Persistence is the time it takes for the
pigments in the retina to bleach (light) or to return to their
unbleached state (dark). The pigments can only turn on and off over
time. The response of the pigments is what allows flicker fusion (not
specifically related to seeing motion), in which we do not perceive a
flashing illuminant to flicker anymore, this includes the cinema screen,
TV, or fluorescent light fixtures.
Motion is a perception which happens solely in the brain. Arguably, the
retina is part of the brain, but we perceive motion as an illusion at
the lateral border of the temporal and occipital lobes (V5) (not the
visual center in the back). The brain constructs objects and motion as
part of the same process, which is why we can sometimes see two objects
as either the same object moving or two separate objects in proximity to
each other. This depends on time. If the time between the viewing of the
first object and the second is half a second or more, then it looks like
two objects. If it is between a tenth of a second and half a second, it
looks like 1 object moving. Hoffman (1998, Visual Intelligence), looked
at brain injury (akinetopsia, primarily) and does a nice discussion
about how they indicate some of the phenomena which relate objects and
motion (see chapter 6 p.139). The smooth motion which we see when
viewing motion pictures is constructed in the brain because we have a
proclivity for constructing smooth motion. Here are some of the rules
which the brain uses for constructing motion. It doesn't matter whether
it is on the big screen or real life:
- Create the simplest possible motions.
- When making motion, construct as few objects as possible, and conserve
them as much as possible.
- Construct motion to be as uniform over space as possible.
- Construct the smoothest velocity field.
The verisimilitude with which we view motion pictures is a result of
these rules.
If you want to dissuade people from thinking that persistence causes the
illusion of motion, I would divorce the idea of motion perception from
notions of persistence. You can relate it to flicker, but not to motion.
I hope this helps.
Alana Parkes wrote:
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related
> institutions.
> *****************************************************************************
>
>
> We're redoing the casework of an old Exploratorium component called
> "Whirling Watcher." It's a slotted disk with drawings of a humming bird.
> When you spin the disk and watch the drawings through the slots in a
> mirror, you see a flying humming bird rather than individual drawings.
>
> Part of the original label describe the phenomenon this way:
> "The light sensitive retina at the back of your eye reacts relatively
> slowly
> to incoming light, so that a quickly changing image remains “inside” your
> eyes for a moment after it is no longer in front of your eyes. This
> effect is
> called “persistence of vision.”"
>
> While researching something else, I came across an article that seemed to
> say that this phenomenon is not, in fact, persistence of vision.
> (citation and
> link below) Before I embark on a more thorough research effort on this
> topic, I thought I would see if someone else has already looked into this
> and decided to change (or not) their label copy.
>
> Thanks for any incites you can share, or even a leg up on my eventual
> research. I'd be glad to know that this paper does not apply to
> phenakistoscopes, or that it is not known to be reputable. Mostly, I'm
> starting from zero on a project I hadn't planned to undertake.
>
> Alana Parkes
> Exhibit Developer
> Museum of Science
> Boston
>
> "The Myth of Persistence of Vision Revisited," Journal of Film and Video,
> Vol. 45, No. 1 (Spring 1993): 3-12.
> http://www.uca.edu/org/ccsmi/ccsmi/classicwork/Myth%20Revisited.htm
>
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Stephen Miles Uzzo, Ph.D.
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