How Our Eyes Deceive Us

The Hebrew Scriptures warn us not to follow our hearts or our eyes because they will lead us astray.

Science is trying to understand why and how our eyes deceive us.

Researchers at the University of Sydney have thrown new light on the tricks the brain plays as it struggles to make sense of the visual and other sensory signals it constantly receives.

“We tend to regard what we see as the real world,” said Dr Mareschal from the University’s School of Psychology.

“In fact a lot of it is distortion, and it is occurring in the early processing of the brain, before consciousness takes over. Our work shows that the cells of the primary visual cortex create small distortions, which then pass on to the higher levels of the brain, to interpret as best it can.”

A common example of this that is often exploited by artists and designers is known as the tilt illusion where perfectly vertical lines appear tilted because they are placed on an oriented background.

(In this tilt illusion, the lines in the centre of the image appear tilted counterclockwise, but are actually vertical) [1]

“The brain seeks more contextual information from the background to try to work out the alignment of the object it is seeing.”

“These illusions happen very fast, perhaps in milliseconds,” Dr Mareschal says. “And we found that even the higher brain cannot always correct for them, as it doesn’t in fact know they are illusions.”

This is one reason why people’s eyes sometimes mislead them when looking at objects in their visual landscape.

The brain uses context, or background, to interpret a host of other visual signals besides the orientation of objects. For example, it uses context to tell colour, motion, texture and contrast. The research will help study how the brain understands these visual cues adding to our overall understanding of brain function.

So the old adage is true… don’t believe anything you hear and only half of what you see. Your eyes and brain may be plotting against you.

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[1] Image adapted from University of Sydney image

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