1. Monocular
Rivalry:
It is difficult to
demonstrate
binocular rivalry on the web, but a good idea of the perceptual
switching
of binocular rivalry can be gained by looking at monocular rivalry. The
alternating dominance of the orthogonal, complementary-coloured
gratings
is similar to binocular rivalry with orthogonal gratings and
seems
to share similar neural mechanisms, thus taking the emphasis away from
binocularity and placing it upon the resolution of ambiguity.
2. Necker
Cube:
3. Animated
Necker
Cube:
The switching may become more apparent in this
version,
especially when the spatial properties of the intruding objects
conflict
with your current interpretation of the figure's perspective.
4. Bonneh's
Illusion: Invented by Yoram Bonneh.
bonneh@nisan.weizmann.ac.il
At first sight this does not seem to be related
to reversible figures. Nevertheless, the cyclic disappearance of the
yellow
discs has many similarities with the cyclic changes of perceptual
rivalry.
The duration of the disappearance-reappearance cycle is correlated with
the binocular rivalry cycle in an individual and the disappearance
phase
can be cut short by disrupting Left hemisphere activity with TMS, just
as with binocular rivalry.
This is the pattern used on the Catalyst program, from which I received
hundreds of emails. Perhaps the most common comment was that the dots
did
not disappear at all. Note that that this does not mean a "slow switch"
, for which one would have to see dots disappear and reappear again,
but
slowly. The most common reasons for the dots to fail to disappear
include:-
stress and tiredness, depression, anxiety, visual problems such as
amblyopia
or loss of vision, neurological problems etc. If the dots fail to
disappear,
try again when you are in a "better mood" (disappearance increases with
euphoria), or at a different time of day.
5. Reversible
Sphere: Horizontal: Yoram Bonneh.
The apparent rotation of the sphere reverses direction, but with a
very long period compared to other rivalry figures. This reversible
figure
also shows considerable plasticity, since the cycle shortens as one's
experience
with the pattern grows.
6. Reversible
Sphere:
Vertical : Yoram Bonneh.
7. Dancer Silhouette:
A popular reversible figure has appeared recently in the Australian
press. This was invented by Nobuyuki Kayahara
and has provoked enormous reaction on the web, along with some
ill-informed criticism. Not many commentators have recognised this as
an example of perceptual rivalry and none that I have seen have noted
our original suggestion that links perceptual rivalry to
interhemispheric switching. It is ventured that a clockwise spinning
dancer indicates a
right hemisphere in control; vice versa for the left hemisphere. This
is consonant with our thesis that the opposite percepts
represent opposite hemispheres and goes a step further by
attributing one hemisphere to a particular direction of
motion.
dancer. We were able to do this recently for plaid
motion rivalry, where the component, "sliding" percept is apparently a
right hemisphere phenomenon, whereas the left hemisphere percept is the
coherent, "diamonds moving upwards" ( see 15 below).
8.Eight
Reversible Spheres: Do you see them all spinning and
switching
together? Or are the directions or spin and time of switches different
for different spheres? I would be very interested in your answers to
these
questions. j.pettigrew@uq.edu.au Note
that
this one may require a click on Reload to get going.
9. Dali's Slave
Market/Voltaire:
Salvador Dali was fascinated by perceptual rivalry and has dozens of
paintings that utilise this aspect of perception. He seems to have
realised
just how ambiguous sensory input often is. I have chosen this painting
because I saw the original in Florida and was unable to see the bust of
Voltaire at first. It became apparent when I changed my distance from
the
painting. If you have trouble seeing Voltaire, move away from the
screen
to make his head have more suitable spatial frequencies to balance the
slave-girl heads.
10. Mona Lisa:
The enigmatic smile of Leonardo's La Gioconda has intrigued
viewers for centuries. Her different "looks" alternate back and forth.
Another example of perceptual rivalry?
11.
Dale Purves' Illusion:
Believe it not, both surfaces have the same
brightness!!
Dale has stressed the ambiguity that exists between
the intrinsic light/dark nature of an object's surface and its incident
illumination.
Is it white-looking because it is made of Carrara
marble, or is it a more dingy stone that is brightly illuminated?
It is impossible to tell from inspection what are
the relative contributions of these two things......the intrinsic
properties
of the object ....and its incident
illumination.
So we have to resort to other information that relies heavily on our
past
experience with illumination, shapes of objects, shadows, brightness of
materials etc.
This illusion is very hard to "shake" but its magnitude may fluctuate
in time, like the other ambiguous perceptions. I would appreciate
feedback
from observers about this possibility.
12. Dale's
Colour Cross:
Also from Dale Purves.
Have a look at the joining region where all the arms of the cross meet.
Most people see the joining region on the Left as a dark grey, almost
purplish
colour, contrasting with the corresponding region on the Right, which
looks
yellow.
Yet they are both physically identical!
You can verify the identity by a stepwise removal of the background
until only the joining regions are showing.
13.
Logvinenko's
Illusion:
In the same class as Dale Purves' illusion, this one is even more
astonishing.
It was met with disbelief by my research group....until they masked off
the surrounding regions.
1 and 2 have the same brightness, as can be checked in the masked
version
on the left.
This is in the same class as Dale Purves' figure. The misperception
may arise from our experience of folded structures like curtains and
drapes,
where we are misled by applying a rule about the constancy of the
drapes'
brightness and colour, even in the depths of shadow.
14.
Adelson's Shadow-checker Illusion:
This is in the same class as 10, 11 and 12, arising fom the
inescapable
ambiguity of colour.
15. Plaid Motion Rivalry:
This is our latest object of study. The switch rate between the
coherent ("diamonds") perception of a plaid and the perception of two
transparent, independently-moving gratings (the component or "slidings"
percept) is correlated with switch rate on binocular rivalry and
Bonneh's motion-induced blindness. In addition, the hemispheric
assignment of each percept is more reliable than it is in binocular
rivalry. The coherent percept seems to be associated with the left
hemisphere while the component percept is associated with the right.
For this reason, there is a very good correlation between mood and the
ratio of the time spent in each percept.
Click here
for plaid motion
rivalry display
This works in Netscape and Explorer, but not in Safari.
Notes on getting the best display:
1. The moving displays, especially 4, 5, 6, and 7, will perform best
if you do not have other greedy software (e.g. Eudora, Powerpoint)
running
in the Background.
2. Another way to get good performance of the display is to save it
as a Favourite in Explorer and then run it from your browser directly
instead
of from the web.
If you have other software running and rely on the web for the display,
you may find that it jogs or stops and starts instead of running
smoothly.
3. You may have to click on Reload to get Display 7 moving.
Volunterering for Perceptual
Rivalry Research: If you enjoyed these demonstrations and
would like to participate actively in the enjoyable and topical area of
resarch, please contacy Bonnie Sheppard at the University of
Queensland, email b.sheppard@uq.edu.au. You will be paid for your
participation. Since we are investigating the effect of mood and mood
disorders on perceptual rivalry, we particularly welcome volunteers who
may have altered moods.