Eyes can tell what we have in our minds

Eyes are not just windows to the soul - they can also tell what we are thinking, a new research has shown.

Researchers at the University of Melbourne have been able to predict the numbers people are thinking of by analysing their eye movements.

In the study, participants were asked to state a series of random numbers. By measuring their vertical and horizontal eye position, researchers were able to predict with reliable confidence the next chosen number - before it was spoken.

Specifically, a leftward and downward change in eye position announced that the next number would be smaller than the last.

Correspondingly, if the eyes changed position to the right and upward, it forecast that the next number would be larger. The degree of eye movement reflected the size of the numerical shift.

First author, Dr Tobias Loetscher of the University of Melbourne's School of Behavioural Sciences and previously of the Department of Neurology, University Hospital Zurich, Switzerland says the research demonstrates how the eyes and their position give insight into the nature of the systematic choices made by the brain's random number generator.

"When we think of numbers we automatically code them in space, with smaller number falling to the left and larger numbers to the right. That is, we think of them along a left-to-right oriented mental number line - often without even noticing this number-space association ourselves," Loetscher said.

"This study shows that shifts along the mental number line are accompanied by systematic eye movements. We suggest that when we navigate through mental representations - as for example numbers - we re-use brain processes that primarily evolved for interacting and navigating in the outside world," Loetscher added.

The study was published online in the prestigious journal Current Biology.