Optical illusions: Not a mystery anymore

Washington, June 3 : While deja vu or ability to see the future is a much debated topic, it is this ability to see into the future that may explain how optical illusions trick us.

How optical illusions actually dodge our concentration is still a mystery. But now a cognitive scientist has said humans have an intrinsic ability to see into the future and that we get a glimpse of events one-tenth of a second before they occur and the mechanism behind this can tell us why we get tricked by optical illusions.

Mark Changizi of Rensselaer Polytechnic Institute in New York has said that the first step in the mechanism is a neural lag, experienced by almost everyone while awake. When light strikes the retina, about one-tenth of a second passes by before the brain translates the signal into a visual perception of the world.

While this lag is common knowledge, still there are debates over exactly how we compensate for this delay. In fact one school of thought has even proposed that it is our motor system that transforms our movements to offset the delay.

But, now Changizi has discovered that it's our visual system that has evolved to compensate for neural delays, by generating images of what will occur after one-tenth of a second. This is what keeps our view of the world in the present. It gives you enough heads up to catch a fly ball instead of getting socked in the face and move without banging with each other while walking in a crowd.

"Illusions occur when our brains attempt to perceive the future, and those perceptions don't match reality," Live Science quoted Changizi, as saying.

This foresight theory can explain the most common visual illusions, i.e. geometric illusions that involve shapes. For example, the Hering illusion, which looks like bike spokes around a central point, with vertical lines on either side of this central, so-called vanishing point.

While looking at this illusion, we think that we are moving forward, and this switches on our future-seeing abilities. And we were not actually moving and the figure is static, we tend to misperceive the straight lines as curved ones.

"Evolution has seen to it that geometric drawings like this elicit in us premonitions of the near future. The converging lines toward a vanishing point (the spokes) are cues that trick our brains into thinking we are moving forward - as we would in the real world, where the door frame (a pair of vertical lines) seems to bow out as we move through it - and we try to perceive what that world will look like in the next instant," said Changizi.

In reality, usually when you are approaching an object, not does its shape changes, but other variables, like the angular size (how much of your visual field the object takes up), speed and contrast between the object and background, will also change.

For example, if two objects are about the same distance in front of you, and you move toward one of the objects, that object will speed up more in the next moment, appear larger, have lower contrast (because something that is moving faster gets more blurred), and literally get nearer to you compared with the other object.

In fact, Changizi said that this future-seeing process could also explain several other types of illusions. He has even made a "grand unified theory," in which he organized 50 kinds of illusions into a matrix of 28 categories. The results can successfully predict how certain variables, such as proximity to the central point or size, will be perceived.

He said that finding a theory that works for so many different classes of illusions is "a theorist's dream." And the majority of ideas put forth to explain illusions have explained one or just a few types.

Changizi said that the theory is "a big new player in the debate about the origins of illusions. All I'm hoping for is that it becomes a giant gorilla on the block that can take some punches."

His research on this topic is detailed in the latest issue of the journal Cognitive Science.

ANI