Science Daily reviews an article published in Current Biology that indicates people give away the size of the number they are thinking about through their eyes. According to the researchers, we tend to look down and to the left when the number we are thinking of is smaller than the previous number, while we look up and to the right if the number is larger. From the article, here is the explanation:
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."
"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."
It's interesting that our eyes shift in response to what we are "looking at" in our mental representations, at least for the majority of us. I wonder what the researchers hypothesize regarding the outcome if they were to assess individuals who cannot read, are blind, etc. I also wonder (as many of the professional poker players probably do, as well) if this can be corrected or altered if an individual is aware of this reflex, or if we are unable to prevent our eyes from acting this way...