We have been working on this striking illusion that was discovered
by
Yoram Bonneh. There are a number of similarities to rivalry (See Carter
and Pettigrew 2003 pdf).
Look steadily at one stationary point, such as one of the yellow discs,
as blinks and sudden eye movements destroy the illusion Notice that
one,
two or all of the yellow discs will disppear and reappear.

We can make the disappearing yellow dots reappear by disrupting the
activity of the left hemisphere using TMS (Funk and Pettigrew
2003 pdf). Alternatively, we can
increase
the duration of the disappearance by disrupting the activity of the
Right
hemsiphere with precisely time pulses (the Right hemisphere seems to be
much more picky about the prcise timing of the TMS pulse than the Left,
perhaps associated with the larger blocks of time dealt with by the
Left ).
Our interpretation is that the left hemisphere is "into denial" as
Ramachandran showed so nicely ( in patients suffering from right
hemisphere
damage, who felt less compelled to deny their paralysis when
right
hemisphere function was temporarily improved by caloric stimulation).
If we are correct, the illusion and perceptual rivalry may share the
same competitive tussle between the right and left sides of the brain.
The disappearance of the yellow discs may thus represent the ascendancy
of the Left, while their reappearance may represent the ascendancy of
the
Right.
Critics have pointed out that there is only one Left hemisphere while
there are a number of different possible patterns of disappearance of
the
yellow discs (8 to be precise). This may be a little pedantic , since
all
of these patterns can be subsumed under one rubric, viz:-
disappearance.
We are presently working on multi-stable perceptions where more than
two
alternatives are possible. These do not seem to present fatal
difficulties
to the hemispheric switching idea so far. In any case, multistable
rivalries
are relatively rare compared to the vast majority of rivalries, which
are
bistable.
Another apparent difference between binocular rivalry and Bonneh's
MIB is that increasing the contrast seems to increase the duration of
the
dominant phase in opposite directions, since brighter yellow dots
increase
the disappearance phase while increasing contrast shortens the
suppressed
phase but has not effect on the dominant phase of binocular rivalry. We
think that it is premature to make too much of this difference, since
there
are some forms of stimulus manipulation (e.g. changing the context)
that
CAN increase the dominance phase duration in binocular rivalry. The
more
monophasic form of the oscillation in Bonneh's MIB might align it more
apporpriately with only one phase of the binocular rivalry oscillation,
for example. In addition, brightening the yellow discs might be seen as
a contextual stimulus in the sense that this would further
separate
the blue swirl from the discs and therefore tend to reject the
hypothesis
that the yellow discs were "connected" to the blue swirl.