The Science Behind Non-verbal Expression Via Dilation of the Pupils

In the realm of nonverbal communication, few things are as expressive as the face. A complex combination of features, the human face can shift and change to produce a staggering array of different messages. Of the many features of the face, the eyes may be the most important to conveying these messages. In the 1960’s researchers J.M. Polt and E.H. Hess studied the eyes, and found that one’s pupils dilate in connection to our interest in a subject, be it another person, an object, or something else all together. In this article, I’ll look at this phenomenon, the theoretical interpretations of such and the importance of this information in relation to non-verbal communication.

The eye itself is a complex organ, made up of several delicate mechanisms which each perform specific functions. The visible part of the eyeball only presents us with a fraction of this intricate body part. The visible parts of the eye are easily recognizable. First is the sclera, commonly referred to as the ‘white of the eye’. It provides an opaque protective housing for the inner functions of the eye which rely upon very specific amounts of light to work properly. Allowing this light into the eye is the pupil, which is essentially the opening through which light passes into the eye. Surrounding the pupil is the iris, a specialized sphincter muscle, adapted for the minute, precision contractions which allow the eye to focus and function in different levels of light. The pupil is the area in the center of the iris, where the unobstructed lens refracts light into the inner eye. Covering the pupil is another lens-like layer called the cornea. As light passes through the cornea, past the iris, through the pupil and lens, it is focused onto the back wall of the eyeball. There, the light stimulates the macula, a collection of photoreceptors which in turn stimulate the optic nerve, sending the visual information gathered to the brain. At the center of the macula is a portion known as the fovea, the portion of the eye which is capable of the most detailed vision. The fovea is literally a fraction of a millimeter in diameter, requiring the focusing mechanism of the iris to function with flawless precision.
When functioning on a purely mechanical, non-expressive level, the iris either dilates to allow more light into the eye, or contracts to block excessive light which may damage or temporarily impair the delicate photoreceptors of the macula. The iris constantly adjusts to maintain sight in changing lighting circumstances. This accommodation occurs at a reflexive level, without conscious thought controlling it.

This unconscious dilation and contraction of the iris becomes an item of interest to the observant communicator when one notes that pupil size sometimes changes in circumstances where lighting is consistent, thus suggesting that it may indicate something beyond adjustment for brightness of light. Researchers E.H. Hess and J.M. Polt studied this phenomenon in the early sixties. While subjects looked at different pictures, they experienced changes in pupil size, and analysis of this information found that there was a direct correlation between one’s interest in an image and the pupillary response; the greater the dilation, the higher the degree of interest.

This information is of particular importance in the realm of nonverbal communication. Externally, the eye is ideally set up to communicate. The black spot of the pupil is surrounded by the colorful iris, and set against the white backdrop of the sclera. Such contrast and color make the eyes distinctively expressive, and make observation of pupil dilation simple.

In applying this information to interpersonal communications, there are three important details one must pay attention to. The first is to be aware of variations in pupil size. Only by observing such dilation does this information become at all useful. Next, one should determine the focus of one’s gaze, to determine the object which produced the dilation response. On a date, it would be inaccurate to attribute the dilation in the other’s eyes as romantic desire if this dilation occurs when they glance at the passing dessert tray. Lastly, be aware of changes in brightness. For example, if one were conversing in an outdoor environment, another person’s pupillary responses may be influenced by clouds blocking sunlight. Changes in lighting activate reflexive dilation and contraction in the eye, which will have little or no bearing on the messages being conveyed from one party to another.

By careful observation, keeping in mind the findings of Hess and Polt, one may gain great insights in their day to day communications. By being attentive to such nonverbal cues in others, one may come to better understand their wants and desires. By understanding their motivations, one may come a step closer to that ideal goal of perfectly clear communication between individuals.