Most think of the pupil as being the part of the eye that expands or contracts to adjust the amount of light entering the eye. This is, of course, correct and is the primary function of the pupil. The pupils of the eyes are under the control of the body's Autonomic Nervous System, a system that operates below the level of consciousness and control most non voluntary functions of the body.
Thus, research has shown that the pupils will also dilate when the body is subject to different stimuli. For instance, a well known fact is that a person's pupils will dilate when they see an attractive member of the opposite sex.
Further it has been discovered that the degree to which a person's pupils dilate can be an indication of their latent IQ. Studies have shown that when presented with difficult cognitive problems, the subject's pupils were seen to dilate in correlation with the degree of difficulty.
It is therefore possible to discern that a person with a high IQ—thus finding the hard problems less "hard"—would show a lesser amount of dilation.
