What? This is the first
visual illusion that is caused by a non-visual cue, namely sound! The illusion
is: when a single flash is accompanied with two beeps, the single flash
is perceived as two flashes. The illusion is strongest when the flash is
in the periphery
but it also works in the fovea.
By Whom? This illusion was discovered
by Ladan Shams, Yukiyasu
Kamitani, and Shinsuke
Shimojo.
How? To see how it works first hand, you
can run the Quicktime movies below. Here is how it works: the eye
icon is the fixation point (i.e., where you are supposed to look at). We
have provided three pairs of movies to accomodate machines with different
CPU speeds. You should first try the top pair which is the highest quality
one. If that does not work, then try the pair below it etc. The movies
on the left are the illusion demos and the ones on the right are just there
for comparison. In both the left and right hand side movies the visual
stimulus is the same--a single flash. In the left-hand-side movies two
beeps accompany the flash whereas in the right-hand-side ones the flash
is accompanied with one beep. Since the visual and auditory stimuli are
very brief, the flash and/or the beep may be skipped by Quicktime. If so,
do not despair ;-), try again and again, and you shall be able to see the
complete movie at least in one of the pairs provided below.
Double Beeps Single Beep
30Hz