Conjuring Up an Image: How our Pupils Adjust to Imagine Light and Dark

For just a minute, try and visualize an image in your mind, such as sunny day or a grey, cloudy night sky. Got it? Now imagine this! Just as you were visualizing those images, your pupils were corresponding to this effect by adjusting to the images of the light.

That's right. That black, circular opening in the center of the iris watches light that passes through the retina and conjures up an image.

A recent study examines how our eyes adjust to the thought of images, especially those involving bright and dark light components.

"Visual imagery is a private and subjective experience which is not accompanied by strongly felt or visible physiological changes," explains psychological scientist and lead researcher Bruno Laeng of the University of Oslo, according to a press release. "It is a particularly difficult topic to research, as years of controversy about the nature of mental imagery testifies."

Patients involved in the study were asked to look at a screen with triangles where different levels of brightness appeared. When they were later asked to actively imagine those triangles, researchers found that the participants' pupils adjusted size based on the original brightness of the triangle. When imagining brighter triangles, for instance, their pupils became smaller. However, when imagining darker triangles, their pupils became larger.

To do this, the researchers monitored pupillary size with an eye-tracking device.

With additional experiments, researchers found that participants' pupils also changed diameter when looking at a sunny skiy or a dark room as well as facing the sun or shade.

The experiments further showed that these results aren't due to voluntary changes in pupil size or differences in the mental effort required to imagine scenes.

"Because humans cannot voluntarily constrict the eyes' pupils, the presence of pupillary adjustments to imaginary light presents a strong case for mental imagery as a process based on brain states similar to those which arise during actual perception," Laeng said, via the release.

More information regarding the study can be found via the journal Psychological Science.