Fancy messing with your senses? Stare at the flashing green dot in the middle of the animation below, and see if you notice anything untoward.
If you stare at the green speck long enough, the three surrounding yellow dots will disappear. This is a phenomenon called “motion-induced blindness” (MIB), a form of illusion that causes a person to lose sight of objects that are otherwise in plain view. Although this may appear to be a failing of your own brain’s visual system, fret not: It is merely a way of filtering out excess information.
GIF credit: Mlechowicz/Wikimedia Commons; CC BY-SA 3.0
A 2008 study by two researchers at Yale University note that these yellow dots may represent a type of scotoma, or “blind spot.” Every mammalian eye has a scotoma in its field of vision: either a location that contains no cells receptive to light (photoreceptor cells) or the position where the optic nerve exists in the retina. Of course, these yellow dots aren’t always invisible to the eye, so they represent a type of temporary scotoma.
According to common theories behind MIB, the reason you are not seeing the yellow dots is due to a phenomenon called sensory overload. As the grid around the green dot rotates, and the yellow dots remain unmoving and unchanging, the brain processes the yellow dots as unnecessary information and blanks them out.
The brain, after all, does not automatically process all information, visual or otherwise, that the body’s sensory systems encounter. If it did, it would overload, so it tends to filter out information that it has repeatedly encountered without change.
The Yale study suggests something else. Instead of the brain automatically removing pieces of unchanging information from view due to sensory overload, the mind is in fact perceiving the objects as contrary to the logic of real-life perceptions. The brain simply does not accept that the object can logically exist based on what information it has. Thus, they disappear from view – they become perceptual scotomas.
The authors suggest that the greater the visual differences between two competing stimuli – in this case, the blue grid rotating around the flashing green dot, and the stationary yellow dots – the more effectively the unchanging parts are able to disappear from view. One experiment even demonstrates that this type of perceptual scotoma can be induced without a moving stimulus, but with changing object brightness.