Motion-Induced Blindness
What to see
On the above you see a rotating array of blue crosses and 3 yellow dots. Now fixate
on the centre (watch the flashing red/green spot). Note that the yellow spots disappear
once in a while: singly, in pairs or all three simultaneously, right?
In reality, the 3 yellow spots are continuously present, honest! This is captively
called “motion induced blindness” or MIB.
What to do
You can change the speed (preset to 12 rotations per minute). Disappearance persists
down to surprisingly slow speeds.
You can adjust the size (preset to 5 pixels). Disappearance persists up to surprisingly
large sizes.
You change the colour of the rotating crosses, the dots and the background. The
dots disappear into whatever colour the background has.
The ‘reset’ button at the top restores the standard
settings.
Comment
Steady fixation favours disappearance, blinks or gaze shifts induce reappearance.
All in all reminiscent of the Troxler
effect, but stronger and more resistant to residual eye movements.
In Feb 2008, John from Phoenix posed an intriguing question in the guestbook: If
several people observe together, do the yellow dots disappearence disappear at the
same time for everyone (synchronised)? I remember I briefly considered this years
ago and rejected the hypothesis of synchronised perception as esoteric. I also informally
tested this, and it did not occur. I still believe that the disappearence is an
individual phenomenon, and thus not synchronised, but this should be formally tested
with careful methodology. Should be an interesting experiment! Anyone?
There is no consensus as to the explanation in vision literature yet. I personally
think that motion is not necessary, any (temporal) change in the image
will suffice. [Note added 2008-03-07: see now Wallis & Arnold, 2008.] A more
recent paper from that group (2009) sugggests a link of MIB to “motion blur / motion
streak” suppression. If so, MIB would be illusion subserving a useful purpose in
everyday vision. This also holds for a different explanatory approach by New &
Scholl (2008) who conclude that “rather than being a failure of visual processing,
MIB may be a functional product of the visual system’s attempt to separate distal
stimuli from artifacts of damage to the visual system itself.”
A simple version of explanation: If you fixate steadily, all structures
are imaged on their same retinal location. This leads to local adaptation on the
retina (the Troxler effect, often incorrectly addressed as “fatigue”). By adding
additional temporal modulation (here the rotation), effectively the background noise
is increased. Thus the Troxler disappearence is more pronouned and/or happens faster.
Sources
Bonneh,
Cooperman & Sagi (2001) Motion-induced blindness in normal observers.
Nature 411:798–801
Wallis TSA & Arnold
DH (2008) Motion-induced blindness is not tuned to retinal speed. JOV 8:11,
1–7
Wallis TSA & Arnold DH (2009) Motion-induced blindness and motion streak
suppression. Current Biology 19:325–329 [website]
New JJ,
Scholl BJ (2008) “Perceptual Scotomas” A functional account of motion-induced
blindness. Psychological Science 19(7):653–659
Created: 2002-10-12
Last update: 2013-10-04