You have more control over your body than you might think. Take your pupils. The small black dots are our window on the ever-changing world. As light waxes and wanes, our pupils contract and dilate. It is, you’d think, a perfect example of your body reacting to the environment on its own, the epitome of the sympathetic nervous system.

But we may have to throw that all out. Researchers have discovered that merely thinking about light or dark can make your pupils contract or dilate. Our mind’s eye, it seems, may have more control over our actual eyes than we thought.

Mechanical though they may be, the workings of pupils are allowing researchers to explore the parallels between imagination and perception. In a recent series of experiments, University of Oslo cognitive neuroscientists Bruno Laeng and Unni Sulutvedt began by displaying triangles of varying brightness on a computer screen while monitoring the pupils of the study volunteers. The subjects’ pupils widened for dark shapes and narrowed for bright ones, as expected. Next, participants were instructed to simply imagine the same triangles. Remarkably, their pupils constricted or dilated as if they had been staring at the actual shapes. Laeng and Sulutvedt saw the same pattern when they asked subjects to imagine more complex scenes, such as a sunny sky or a dark room.

The research is important because it adds to a growing wealth of knowledge regarding how consciousness works. It also contributes to neuroscience’s understanding of the complexity of vision . By comparing and contrasting studies in which visual stimulation is externally induced with those where visual stimulation is psychologically stirred, scientists might be able to provide hard data to question that have long been rooted in pure philosophy.

Discover another way in which the mind influences the eye by watching this NOVA scienceNOW segment, "Change Blindness."