Scientific American magazine ran an article back in the 1970's about
experiments with headphones.  Put 440 Hz into one ear, put 442 Hz into
the other.  Do you hear beats?  Turns out that it depends on the person
and that this ability has some considerable significance in brain
research.

Psychoacoustics is an interesting and thoroughly legitimate field of
study.  It has, however, been used in the not-so-scholarly field of
home audio equipment sales pitches.  You can, often enough, convince
someone that one speaker or amplifier sounds better than another.
This kept the ball rolling in the stereo business for years, and it
still seems to work in the world of high-end audio.

The same techniques do not work very well if you're trying to sell TV
sets.  Vision seems to be different, for reasons that we've been trying
to determine for many years.

Both vision and hearing are unbelievably complicated.  A good deal of
the research still revolves around optical illusions and the 'aural
illusions' mentioned in this thread.

Mark Kinsler
Lancaster, Ohio USA
http://home.earthlink.net/~mkinsler1