I was giving a presentation on early film to an audience of non-academics
last Friday and was explaining a bit about its pre-history and the
persistence of vision when an incredibly astute first-grader--in an
audience otherwise consisting entirely of adults--asked me if it could be
used to explain why wheels which are going forward sometimes appear to be
going backward or in reverse of the direction they ought to be spinning
when they are filmed. Yow. (After my talk, the series organizer mentioned
to me that this shrewd little guy causes his first-grade teacher a great
deal of angst and suffering.)
 
So I'm kicking the question back to the film list. Can anyone answer this
for me? Why do wheels, when filmed, sometimes look as if they are
spinning in a direction which appears to be the opposite of the direction
which logic tells us they actually must be spinning? Does persistence of
vision have anything to do with it?
 
Also, David Cook's book mentions something called the phi phenomenon
which combines with persistence of vision to produce the effect of
continuous motion in film. His explanation of what the phi phenomenon is,
is not very satisfying, but none of my other film textbooks (Monaco,
Bordwell and Thompson, Abel, Gollin) seem to elaborate the phi phenomenon
much more than Cook, if indeed they mention it at all. I'm not quite sure
if I can distinguish a difference between persistence of vision and the
phi phenomenon, given the way he explains it.
 
Does the phi phenomenon have something to do with this wheel thing? Is
there a good journal article or something out there in language which I
can grasp? Awhile back, I read some stuff by perception psychologists,
hoping to find more about these film effects, but it was more mystifying
than helpful. I remember reading something in a book edited by de
Lauretis--THE CINEMATIC APPARATUS?--but, as I recall, the conclusion was
something along the lines of "current models of the persistence of vision
are unsatisfying, and we need to re-examine them." But I don't
remember--or perhaps did not grasp--the updated model.
 
Does anyone have a good sound bite about this which they are willing to
share? Or at least can someone explain that wheel thing in case I bump
into any more armed and dangerous, precocious first graders?
 
Thanks--
 
Meryem Ersoz
University of Oregon
 
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