## Motion-induced Blindness Illusions

posted on 6 May 2014 by guy
last changed 25 May 2016

 5 Average: 5 (1 vote) Select ratinghated itdidn't like itliked itreally liked itloved itCancel rating Your vote (click to rate)ages: 14 to 99 yrs budget: $0.00 to$0.00prep time: 0 to 5 min class time: 5 to 20 min Motion induced blindness illusions use apparent background motion to make static portions of the visual field temporarily disappear from view. They produce an effect that seems similar to the blind spot in the eye, or the disappearance of images in Cheshire cat illusions, but which apparently has a different cause. Younger students can enjoy the illusion in its own right, while older students can speculate about the cause of the effect, which is still not completely understood.
subjects: Biology, Psychology
keywords: motion, blindness, desensitization, optical illusion

## try the illusion

Stare at the yellow-green flashing dot in the center of figure 1. Without moving your eyes, try to pay attention to the surrounding three yellow dots with your peripheral vision. You should notice that the surrounding dots disappear from time to time, singly or in groups, and then reappear. This effect is called "Motion-induced Blindness" (MIB).

## what's going on?

MIB was originally discovered by Ramachandran and Gregory in 1991.1 There is not yet concensus on the precise neurological mechanism that is responsible, but several ideas have been proposed over the years.

## not desensitization

MIB produces an effect similar to a blindness illusion caused by neural desensitization, but is probably not directly related.

It's well known that static images can be made to disappear under certain circumstances. Images that stay in a fixed place on the retina quickly fade away due to desensitization of light sensitive cells in the retina. This desensitization (a.k.a. "adaptation" or "bleaching") is the reason we do not normally see the shadows of blood vessels that lie on top of the retina. (See our lesson on Seeing Blood Vessels in the Eye for more details.)

Most images on the retina are not subject to desensitization. Small involuntary eye movements ("tremors") move the image around on the retina, changing the illumination on the light sensitive cells, thereby guaranteeing that they never completely desensitize. However, some low-contrast, blurry images can reduce the effect of eye tremors and allow desensitization to take place. See our lesson on Cheshire Cat Illusions for examples.

The illusion in figure 1 seems to be produced by a different mechanism. The dots that disappear are small, sharply-defined and have high contrast. Normally, tremors in the eye should prevent them from desensitizing particular cells in the retina. In this case, the disappearance seems to depend critically on the changing background.

## possible explanations

attention focus — One suggestion for the cause of MIB has to do with the focus of attention.2 Perhaps the brain is simply distracted by the changing image and fails to pay attention to static portions of the visual field. In this respect, MIB may be similar to an effect produced when two different images are seen by the two eyes (binocular rivalry). In that case, the brain tends to focus on the image in one (dominant) eye, to the exclusion of the image in the other eye.

suppression of eye movements — There is some evidence that some eye movements are partially suppressed in the presence of background motion.3 In that case, the reduced eye motion may allow desensitization to occur, as it does in Cheshire Cat Illusions. However, more recent studies of eye movements in MIB experiments4 claim that eye movement suppression is not adequate to allow significant desensitization.

filling in the gaps — Some research has suggested that MIB might be related to a known effect called "perceptual filling-in",5 which explains why we don't see the blind spots in our eyes. In the absence of sensory input for portions of the visual field, the brain fills in the missing parts with information from surrounding areas. (See our lesson on Blind Spot for activities to explore the blind spot.)

contrary to logic — It has also been suggested6 that if a static image is inconsistent with the motion of its background, the brain may discount the static image as contrary to the logic of the scene, perhaps akin to how it ignores the blind spot in the eye.

streak suppression The eye and brain integrate the visual image over time. For images that are moving, this integration produces streaking in visual perception, like the streaking in a long exposure photograph of fast motion. The brain actively suppresses the streaking in order to make better sense of the image. This suppression may account for some or all of the MIB effect. Research has demonstrated7 that MIB is enhanced at the trailing edge of motion, which supports this idea.

## motion-induced blindness in everyday life

Figure 2 shows an example of motion-induced blindness with everyday objects, demonstrating that the effect works with static images that are not just simple dots. Although it's hard to find examples of motion-induced blindness in everyday life, there is concern over the possibility that MIB could play a role for pilots and drivers. Fixing your gaze on the traffic straight ahead while driving down the highway (with the background scenery apparently in motion) could conceivably make you blind to a car passing you on the side. Pilots have long been advised to continue shifting their gaze, never fixing on any one point for more than a couple seconds lest they fail to notice something important. See http://www.arrivealive.co.za/print.aspx?s=5&i=2999 for a discussion of these concerns.

## teaching notes

This lesson follows nicely after a study of Cheshire Cat Illusions in order to compare the differences in the two effects. Cheshire act illusions require low contrast, low resolution static images, while MIB illusions can work with high-resolution high-contrast images, but require a changing background.

Use Michael Bach's version of the illusion to allow students to study how the MIB effect depends on color, dot size, and rotation speed.

The underlying cause of motion-induced remains a matter of debate. It is a great example of experimental science at the forefront, before a widely accepted explanation is in place. For students who already have some experience in scientific thought, it offers an opportunity for open-ended speculation.

Ask students to consider which of the above explanations might be most plausible and why. See if they can come up with other possibilities. Have them brainstorm about how to explore each of the explanations further. What dependent parameters (such as the frequency and duration of disappearances) would they look at in order to measure an effect on MIB?

Some topics that researchers have already explored include:

1. To study how attention plays a role in MIB, subjects have been asked to focus on different targets (the center of the screen, the static images, the rotating background) while looking at MIB images. What if the subject is asked to concentrate on another task (such as a mathematical calculation) while looking at a MIB image?
2. In order to try better understand how eye movements are connected to MIB, researchers can track eye movements of subjects by measuring reflections in the eye, and using computer analysis to calculate what direction the eye is pointed. This measurement can measure the size of eye movements in MIB experiments, and determine if they are small enough to allow neural desensitization. See figure 3 in the online article at http://www.scholarpedia.org/article/Motion_induced_blindness for an example of eye tracking measurements. (These authors think that eye movements are too large to allow image stablization and desensitization.)
3. Some research has made use of the differences in left and right brain activity to study how the brain handles the different sensory input of stationary and moving images in MIB experiments. The left brain sometimes seems to suppress sensory information that conflicts with its model of the world; the right brain more likely sees the world the way it really is. In MIB experiments, there may be a conflict of interpretation between static and moving images that causes the brain to suppress the static parts. One experiment8 used magnetic pulses to temporarily disrupt left or right brain activity, noticing a correlation with MIB that suggested these higher level processes in the brain may contribute.
4. To study the role of streak suppression, researchers have compared MIB activity both in front of and behind background image motion. Increased MIB at the trailing edge of background motion suggests this mechanism might contribute to MIB.

## further resources

Michael Bach hosts a wonderful library of optical illusions. His version of the motion-induced blindness illusion allows adjustment of various independent parameters (color, resolution, dot size).

For those wanting more advanced discussion of the MIB effect, the article by Bonneh and Donner at http://www.scholarpedia.org/article/Motion_induced_blindness provides a thorough overview.

• 1. Ramachandran, V. S.; Gregory, R. L. "Perceptual filling in of artificially induced scotomas in human vision". Nature 350 (6320) (25 April 1991): 699–702.
• 2. Bonneh, Cooperman & Sagi "Motion-induced blindness in normal observers". Nature 411(2001):798–801.
• 3. New, J. J.; Scholl, B. J. "Perceptual scotomas": a functional account of motion-induced blindness". Psychological Science 19 (7) (July 2008): 653–659.
• 4. Bonneh, Y. S., Donner, T. H., Sagi, D., Fried, M., Cooperman, A., Heeger, D. J., et al. "Motion-induced blindness and microsaccades: cause and effect". Journal of Vision, 10(14) (2010): 22.
• 5. Hsu, L. C.; Yeh, S. L.; Kramer, P. "Linking motion-induced blindness to perceptual filling-in". Vision Research 44 (24) (November 2004): 2857–2866.
• 6. New, J. J.; Scholl, B. J. "Perceptual scotomas": a functional account of motion-induced blindness". Psychological Science 19 (7) (July 2008): 653–659.
• 7. Wallis TSA & Arnold DH. "Motion-induced blindness and motion streak suppression". Current Biology 19 (2009):325–329
• 8. Funk A P, Pettigrew J D, 2003, "Does interhemispheric competition mediate motion-induced blindness? A transcranial magnetic stimulation study" Perception 32(11) 1325 – 1338.