Re: how much of what we see is black?

From: Flick Harrison (email suppressed)
Date: Wed Oct 31 2007 - 11:10:07 PDT


Are you suggesting that myths are less useful for artists than science?


Well, I was taught about persistence of vision straight out of the
textbook in 1994 at film school, which is reason enough to be
skeptical. Ha ha.

But it seems like the Andersons spend a lot more time explaining
different types and implications of motion perception than
"debunking" the myth of persistence of vision. You'll notice I
didn't actually conflate the two.

P.o.v. is a physiological concept. Not psychological.

I have no idea if it's a scientifically correct explanation of the
failure to perceive black between film images, though I have yet to
hear a better explanation.

But that paper you linked to does nothing to debunk it! It could be,
as Herbert suggests, that we are simply ignoring the black - Occam's
razor leans this way - but that's not proof.

(the unattributed stuff in Herbert about after-images is worth more
checking out, though it doesn't disprove p.o.v. by suggesting another
phenomena takes place later).

Good reading though, and I appreciate the challenge to my long-held

The reference to Munsterberg is especially, hilariously weak. Perhaps
his original articles are much more substantial.

When I see a scientific paper that says, "no part of the vision
system remains stimulated for any measurable length of time after the
last photon hits it; retinal nerves reset themselves to neutral
within less than 21 milliseconds (1/48th s)" then I'll believe it.
Proszynski isn't a neurologist; he made projectors.

If p.o.v. is the wrong term (flicker fusion?), or scientists can
divide it up into multiple concepts, then ok.

I would enjoy a p.o.v. wikipedia update coming from this discussion.

I said: the illusion of continuous image is a factor of p.o.v. (or
whatever physiology calls it) Motion-illusion is a separate thing.
You can get a motion-illusion from a flipbook, though you'll still
see, faintly, the flipping pages themselves. They aren't moving fast
enough to completely disappear. At below 18 fps projection, you'll
get motion-illusion but you'll see flickers. In fact, the illusion of
motion can happen even at incredibly slow shutter speeds, with long
periods of black in between (though not SMOOTH motion). But a half
second of black will definitely register on your brain; 1/48th second
of black won't.

Film Journals aren't exactly the place for hard science (and neither
is film school, apparently). Especially when the writer of this essay
seems to be attacking "19th century" (i.e. assumed outdated) Marxist
and Psychoanalytic film theory through this back channel, in addition
to DB's critique of his objectives.

"From our present perspective it seems reasonable to ask why film
scholars have been content for most of the twentieth century with a
nineteenth century explanation of the apparent motion in motion
pictures. But then, we could just as well ask why they have
contented themselves with a nineteenth century explanation of mind
(Freud's psychoanalytic model) or a nineteenth century explanation of
society (Marxism). The answer is not readily apparent. "

Seriously: why shouldn't a 19th century explanation be fine and dandy
for a 19th century phenomenon like Cinema? My bike works fine and
it's essentially a 19th-century design.

(And here we are using a 20th-century-style usenet discussion group
instead of a 21st-century virtual world, har har).

They call p.o.v. "a totally inadequate explanation of the illusion of
motion in the cinema." Not an incorrect explanation for flicker
fusion, i.e. the illusion of continuous image.

There's plenty more bad logic in the next couple paragraphs.

Their interpretation of Roget's work in their original "Myth of
Persistence of Vision" essay

skips over the whole 1/48th-of-a-second-blackness issue, because they
conflate "after-images" left by a very bright light, which stay in
one place in your eye and can last for some time, versus the medium-
bright overall image which *might* persist only for 1/48th of a
second. You can move your head around while watching a movie, they
seem to argue (though they are using the bicycle-spoke example rather
than cinema itself), and the movie still seems to be continuous,
rather than becoming jerky and blocky as the sequential after-images
fail to line up. Therefore no afterimages exist.

But this obviously assumes you are moving your head around fast
enough to cause a significant difference - more difference than, say,
an object moving quickly across a giant cinema screen image - within
1/48th of a second. Heads don't move that fast. And if they did, it
would no doubt alter the perception of the image, assuming the info
from your inner-ear fluid wouldn't clear up the confusion.

"Clearly, a simple fusion of a succession of images would not result
in the perception of motion. It would result in the perception of one
composite, still image. "

This is a straw man because no one is suggesting that ALL the images
persist forever. It's sequential. One image persists only long enough
for the next image to pop up.

The whole argument of the Andersons is based on refuting persistence-
of-vision by substituting "illusion of motion" halfway through the
argument: There is no such thing as persistence of vision because the
illusion of motion cannot be entirely explained by it. There is no
dog in my house because there is plenty of dog food left.

Over and over, they argue that "processing" of the image doesn't take
place in the retina, therefore no p.o.v. exists.

I've never heard anyone suggest that processing takes place in the
retina (unless it's like film processing, ie. converting visible
light into photo-electric brain-readable information). The p.o.v idea
is that the retina retains the image and sends it on to the brain as
if it were still happening. The brain processes it and that's where
the illusion of motion takes place.

I could write more but bla bla bla bla bla.


On 30-Oct-07, at 1:59 PM, Todd Eacrett wrote:

> The myth of persistence of vision was first debunked 30 years ago:
> 20Revisited.htm
> Todd Eacrett
> ----- Original Message -----
> From: Flick Harrison <email suppressed>
> Date: Tuesday, October 30, 2007 1:28 pm
> Subject: Re: how much of what we see is black?
>> Hate to be a splitter.
>> We don't actually "see" any blackness at all. From our point of
>> view, there is no blackness.
>> Aside from the witty comment on here that you can't see
> blackness
>> (it
>> is the absence of an image, so it's more like not-seeing).
>> Persistence of Vision is the phenomena wherein your optic nerve
> (or
>> whatever) takes time to "reset" i.e. cool down and stop
>> transmitting
>> the last image you saw.
>> Frame rates which create the optical illusion of continuous
>> movement
>> are using this phenomena.
>> The image stays in your optic nerve while the shutter closes,
>> advances the frame, then re-opens just in time for your optic
> nerve
>> to absorb a new image.
>> Your eye / mind never notices the blackness because it's not fast
>> enough to see it.
>> I.o.w., your eye is fooled into thinking there is no darkness. The
>> darkness is too short for you eye's mechanism to register.
>> It;s not like the optical illusion of a bunch of dots becoming a
>> straight line as you pull back. That is simply perceptual / mental
>> illusion, at least until you get back so far that the dots fall
>> below
>> the resolution of your eyeballs.
>> It's more like an optical override.
>> To be clear - continuous motion on screen is an optical illusion,
>> created by a series of still pictures. Continuous brightness on
>> screen is a neurological illusion, not an optical one - though
>> that's
>> splitting optic nerve-hairs.
>> * BLOG / NEWS:
>> On 30-Oct-07, at 6:53 AM, Yoel Meranda wrote:
>>> A question I'm curious about...
>>> When a film projector is running, what is the percentage of
> time the
>>> light is interrupted by the shutter? In other words, what
> percentage
>>> of what we see is darkness?
>>> I realize that this question will have different answers for each
>>> projector...
>>> I am mostly curious about 35mm projectors but any clue on
> any other
>>> projector would be great. Even guesses would be fine if no one
> has
>>> concrete answers.
>>> Thanks,
>>> yoel
> _________________________________________________________________
> _
>>> For info on FrameWorks, contact Pip Chodorov at
> <email suppressed>.
> _________________________________________________________________
> _
>> For info on FrameWorks, contact Pip Chodorov at
> <email suppressed>.
> __________________________________________________________________
> For info on FrameWorks, contact Pip Chodorov at <email suppressed>.

For info on FrameWorks, contact Pip Chodorov at <email suppressed>.