A team of researchers at the University of Sydney has completed research detailing how the brain reacts to the bombardment of visual and other sensory signals it constantly receives.


The research has broad implications for the understanding of the process used by the brain for interpreting the world visually, and how the brain itself works.


In an article published in the Proceedings of the National Academy of Science, Dr Isabelle Mareschal and Professor Colin Clifford from the University of Sydney’s School of Psychology and the Vision Centre, report a series of ground breaking experiments tracing the origins of a number of illusions to the cells of the primary visual cortex. 


"We tend to regard what we see as the real world," said Dr Mareschal.


"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.


"We wanted to test at what level the illusion occurs in the brain, unconscious or conscious - and also to see if the higher brain is aware of the illusions it is receiving and how it tries to correct for them," she explains.


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


The team subjected volunteers to a complex test in which they indicated the orientation of a vertical line, perceived as constantly tilting from side to side, against a fuzzy background that was also changing.


"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."