As I read the two answers referenced by Tom, they both talk about stroboscopic motion. (The first says it _ordinarily_ requires strobe light, but doesn't say any more about seeing it when light is steady.)
I have often noticed what looks like stroboscopic motion from looking into the front of a jet engine, and sometimes at propellers. I have wondered, but not enough to look it up.
don
Donald McBurney


Dennis Goff wrote:

Tom,
Take a look at http://www.newton.dep.anl.gov/askasci/gen01/gen01404.htm. Be sure to read both answers. The first answers indicates that the illusion won't happen under steady lighting. The second answer indicates how the illusion could happen under that condition. Hope it helps
Dennis


-----Original Message-----
From: Tom Allaway [mailto:[EMAIL PROTECTED]
Sent: Thursday, April 01, 2004 9:40 AM
To: Teaching in the Psychological Sciences
Subject: A Perception Question



   In a class discussion of the phi phenomenon the other day, the talk
drifted around to stroboscopic phenomena, and the
"wagon-wheels-turning-backward" illusion that you get with films or TV.
I explained this briefly, but several of my students said that it didn't
depend on a flashing or intermittent source of illumination, as they
frequently saw this effect in broad daylight, on the wheels of moving
cars (especially those with wire wheels).  I told them I didn't
understand how that could be.

Can you get this illusion under continuous illumination? How?




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