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Physiological Measurement: Pupillary Response

A lot of poetic and philosophical statements exist about the eyes, such as the eye represents the “window to the soul.” Literature on romance and relationships often indicate a desire for persons to look into the eyes of the other, as if such an examination would provide clarity or meaning. Clearly, the reactions that take place in the eyes of a person constitute a visible reaction that someone can observe. Much as with any observed reaction, the research focuses on how to draw meaning from these observations. What does any change or reaction on the part of the elements of the eye, particularly the pupil, indicate about the person’s mental state? Both observing the reaction and then correctly drawing a conclusion about what the reaction indicates provides a challenge for research. As with most research dealing with physiological measurement, the observer views the reactions of the eyes and then makes inferences about the associated message. For example, a person may become “wide eyed” indicating surprise or shock in response to information, the lack of such a response may be viewed as a lack of surprise. The increase or decrease, or nonresponsiveness of the pupil to particular stimuli becomes interpreted as an indication of a mental state. This entry introduces pupillary response and offers insight into how pupillary responses are measured and analyzed in communication research.

The History of Research on Pupillary Response

The origin of the study of eyes and other behaviors dates back to the work of Charles Darwin back in the 1860s and 1870s. In formulating what became the theory of evolution, Darwin was examining how species of animals each provide examples of common physiological responses across species. Part of his argument was that the development of the set of common responses indicates a common origin that may provide evidence linking various species.

One of Darwin’s assumptions was that the various needs for vision would create the need to modify and focus the eye as tool of vision. The argument was the animals (including humans) would have evolved to create a means of improving or adapting eyesight (when needed) to increase the probability of survival. Since the laws of physics work the same for all species, the development across species should show great signs of similarity. The argument he wished to make was that in response to environment each species would demonstrate similarities that make survival more possible. What Darwin was examining was how the eye responded to a stimulus like danger (threat) or affection (safety). He hoped to determine whether such responses were the same across species. The question of how the eye responds or changes in response to some change in the environment provides the basis for much of the research using this approach. The particular animal would respond to the environment by adapting the eye to the conditions to increase the effectiveness of vision.

Understanding the Change in the Eye

Essentially, two basic changes or eye behavior serve as a basis for most research in the area: (a) size of the pupil and (b) focus of the eye gaze direction. Often this research involves a great deal of focus on biometrics and employs a variety of devices to measure the changes associated when observing this physiological behavior. For example, some version of the pupillometer is used that records and measures the size of the pupil and can track changes over time. The pupil is the part of the eye involving the iris through which light passes. The amount of light becomes controlled by either increasing or decreasing the size of the iris in response to the need to improve vision or react to various environmental conditions (e.g., contraction takes place when a light is shone on the eye). The “light reflex” simply indicates that in response to low light the pupil dilates to increase light flow and will constrict when a great deal of light is available. The response of the eye combines a combination of physiology that is motivated or exerted by the person indicating the desire to look or increase the clarity of vision. Specifically, the lens of the eye becomes something that the animal will use to make vision more effective and increase clarity of vision.

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