> "Transitions from one percept to its alternative are called perceptual
> reversals. They are spontaneous and stochastic events which cannot be
> eliminated by intentional efforts (although some control over the
> alternation process is learnable). Reversal rates vary drastically between
> stimuli and observers, and has been found to be slower for people with
> Bipolar disorder ("sticky" interhemispheric switch in bipolar disorder)
> [1]."
>
> http://en.wikipedia.org/wiki/Multistable_perception#Characterization
>
> Added 11/22/06:
> 'Impossible objects' exist as two dimensional vectors which can be defined
> by Cartesian Coordinate systems. As such, the 'objects' do not exist as
> 'true three dimensional forms', and in this context are identical to the
> perception of 'paint' on a wall, that is: 'color'. Or, similarly, a 'skin'
> defining form. Thus, 'impossible objects' can be defined as a 'visual'
> tautology, the ambiguity of the apparent object being nothing more than the
> result of self-referential perceptual conventions.
> ...