In the center panel, you see the person’s pupil at rest, after being exposed to normal indoor lighting conditions. The pictures were taken using an eye-tracker blue coloration indicates the location and size of the pupil.Figure 2 - In this figure, you see the same person’s pupil in three different states.
Pupillary responses, then, can partly be understood as involuntary or unconscious physical responses to lighting conditions, but this is actually just the tip of the iceberg! (see Figure 2). The autonomic nervous system-the part of the nervous system responsible for unconscious and involuntary processes, which are processes that we cannot consciously control, like heartbeat and digestion-is also responsible for the pupillary light reflex. This is called the pupillary light reflex. When lighting is dim, the iris responds by dilating (relaxing)-making the pupil larger for situations in which more light is needed to see. When lighting is intense, the iris responds by contracting (flexing)-making the pupil smaller and thereby allowing less light into the eye. The light is absorbed/captured at the back of the eye/camera by the retina/film (shown in purple at the back of the eye, and in purple on the camera, behind the lens). The iris/diaphragm adjusts the size of the pupil/aperture to allow the appropriate light into the eye/camera. The iris (shown in green at the front of the eye, surrounding the pupil) is similar to the camera’s diaphragm (shown in green at the front of the camera lens) and the pupil (the small opening at the center of the eye) is similar to the camera’s aperture (the black opening at the center of the camera lens that allows light in).Figure 1 - An analogy can be made between a camera and the eye.
Photoreceptors gather information from the light and send it to the brain to be processed into the image you see. The retina is covered in specialized cells called photoreceptors (think of this part of the eye as the film of a camera where the picture is captured). Light travels through fluid in the eye and is then absorbed at the back of the eye, in an area known as the retina. The iris responds to the amount of light entering the eye by adjusting the size and diameter of the pupil (the aperture), in order to allow the appropriate amount of light into the eye (the camera). The iris is a muscle in the eye that functions like the diaphragm of a camera (see Figure 1). The pupil is the opening at the center of the eye that appears as a black dot surrounded by the colored part of the eye, the iris. The opening at the center of your eye allows light to enter it, enabling you to gather information about the world around you, but the opposite is true, too-insights can be gained about what is going on in your brain based on the behavior of your pupils.
As you will discover, the small opening at the center of your eyes can tell us a whole lot about what is happening in your brain! In this article, we will discuss how pupils function, how they respond to environmental stimuli, and how their reactions are reflective of cognitive processing-that is, the inner workings and computations going on in the mind. The pupils also respond when people ingest certain drugs, when they feel strong emotions, when they retrieve a memory, or when they are concentrating or thinking very hard about something. But environmental responses-like the response to light-are just the tip of the iceberg. When the environment is bright, the pupil constricts, and when it is dim, the pupil dilates. But a lesser known fact about the pupil is that by closely examining how it constricts (gets smaller) and dilates (gets larger) in response to certain stimuli, scientists can gain crucial insights about what is going on in the brain. Your pupil, the opening at the center of your eye, allows you to gather information from the world around you.
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