As seen in the video above the yellow jacket (Rocky, the mascot of the University of Rochester) appears to be expanding. But he is not. He is staying still. We simply think he is growing because our brains have adapted to the inward motion of the background and that has become our new status quo. Similar situations arise constantly in our day-to-day lives — jump off a moving treadmill and everything around you seems to be in motion for a moment.

This age-old illusion, first documented by Aristotle, is called the Motion Aftereffect by today’s scientists. Why does it happen, though? Is it because we are consciously aware that the background is moving in one direction, causing our brains to shift their frame of reference so that we can ignore this motion? Or is it an automatic, subconscious response?

Davis Glasser, a doctoral student in the University of Rochester’s Department of Brain and Cognitive Sciences thinks he has found the answer. In their paper, the scientists show that humans experience the Motion Aftereffect even if the motion that they see in the background is so brief that they can’t even tell whether it is heading to the right or the left.

Find more here Neuroscientists find famous optical illusion surprisingly potent.

Interestingly, we found the affect still worked after watching the video and then looking at a page of text on a piece of paper or a web site – Optical Spy

New research by psychologists at Queen Mary, University of London has revealed that the way we see the world might depend on reflexes in the brain. Writing in the Journal of Vision, Dr Michael Proulx from Queen Mary's School of Biological and Chemical Sciences, and former student Monique Green, explain how an optical illusion known as the Müller-Lyer Illusion captures our attention more strongly than other visual tests, suggesting that the brain calculates size as a reflex fast enough to guide where the eyes look.

The Müller-Lyer illusion was first described by F.C. Müller-Lyer in 1889, and is one of the most famous size illusions. He found that two lines of the same length can be seen as longer or shorter by simply adding arrow heads that point in or out at either end.

In this study, Dr Proulx and Green asked participants to search for a vertical line among distracting lines tilted to the left and right. All of the lines had arrow heads at either end that randomly pointed in or out, making some lines appear to be longer or shorter than others due to the illusion. They found that the line that appeared to be the longest captured the participants' attention the most. Dr Proulx explains: "The surprising difference here is that the perceived longer line not only captured their attention, but was even more distracting than the sudden appearance of something new as shown in prior research.

"This suggests that many visual illusions might be so effective because they tap into how the human brain reflexively processes information."

Optical Spy note - The illusions shown here have nothing to do with this latest research, but we thought you might enjoy an example of the famous Muller-Lyer illusion.

An Ames room is a distorted room that is used to create an optical illusion. Probably influenced by the writings of Hermann Helmholtz, it was invented by American ophthalmologist Adelbert Ames, Jr. in 1934, and constructed in the following year.

An Ames room is constructed so that from the front it appears to be an ordinary cubic-shaped room, with a back wall and two side walls parallel to each other and perpendicular to the horizontally level floor and ceiling. However, this is a trick of perspective and the true shape of the room is trapezoidal: the walls are slanted and the ceiling and floor are at an incline, and the right corner is much closer to the front-positioned observer than the left corner (or vice versa). (See overhead view diagram)

As a result of the optical illusion, a person standing in one corner appears to the observer to be a giant, while a person standing in the other corner appears to be a dwarf. The illusion is so convincing that a person walking back and forth from the left corner to the right corner appears to grow or shrink.

Studies have shown that the illusion can be created without using walls and a ceiling; it is sufficient to create an apparent horizon (which in reality will not be horizontal) against an appropriate background, and the eye relies on the apparent relative height of an object above that horizon.