Brain balances perception and action when caught in illusion, suggests a new study at the University of Oregon.
In a two-experiment study, neuroscientists Paul Dassonville and Scott A. Reed used eye-tracker technology in a dark laboratory to test a developing theory about how the brain determines the locations of nearby objects.
In a test of perception, 20 students were asked to report whether a line was tilted left or right of vertical. Their performance in this simple task became skewed, however, when the line was shown within a tilted frame. A left-leaning frame caused the line to appear tilted to the right, and vice versa.
In spite of this well-known visual illusion, when subjects were asked to look at the end of the line they had no trouble making accurate eye movements, demonstrating an apparent difference in the way that perception and actions respond to the illusion.
Similar demonstrations have led other researchers to suggest that the brain forms two maps of space, an illusion-prone map for creating conscious perception of the world, and an illusion-resistant map used for guiding movements.
Results of the new experiments showed that accurate eye movements to the end of the line prove to be the exception, rather than the rule. When subjects were instead asked to make simple vertical eye movements, for example, those movements were affected by the tilted frame just as visual perception had been.
Dassonville said that the perceptual illusion caused by the tilted frame is analogous to a treasure map that is created using the faulty compass. The map is technically incorrect, but as long as you use the combination of the faulty map and the faulty compass to navigate around, you'll be able to accurately find the treasure once again. The errors cancel out.
In the experimental task, the cancellation of errors allowed the subjects to make accurate movements to the end of the line in spite of the illusion.
Reed added that they found that the brain relies on a shared representation of space that is used to both make perceptual judgments about the world and to guide behavior.
The study is published in the journal Frontiers in Human Neuroscience