[From Rick Marken (2000.12.27.1530)]
But how could a perception be invalid?
Many ways. Perceptual illusions, for one...
Bruce Gregory (2000.1227.1626) --
A perception is a signal in the input to a control system.
I don't see how a neural signal can be "an illusion". As
far as I know, a neural signal is a neural signal.
I'd say an "invalid" or "illusory" perception (neural signal)
is one that does not map as expected to the physical variable
to which it presumably corresponds. For example, the size of
the moon is a perception (neural signal) that is a function
of some set of physical variables, including the size of the
moon itself. The _perceived_ size of the moon is much larger
when the moon is near the horizon than when it is high in the
sky. This is called the "Moon illusion" because science tells
us that a) the moon itself is the same size no matter where it
is in the sky and b) the optical size of the moon is also
the same no matter where it is in the sky. So we have a
perception (neural signal) of moon size changing when the
physical variable to which it presumably corresponds (the
size of the moon itself) does not change. I (and just about
every other psychologist in the world) would call this an
"illusion" or an "invalid perception". The perception is
invalid because it does not correspond to our _model_ of
the reality that corresponds to the perception.