A variety of psychological and physical conditions can cause variations in the diameter of the pupil—the black center of the eye that changes in size to regulate the amount of light reaching the retina and to sharpen images. In an article published in Psychophysiology, experts offer a set of guidelines to inform and guide research involving pupil measurements during psychological research.

Pupil diameter is changed as muscles of the iris expand or contract in response to the activity of neurons and hormones. The guidelines summarize important aspects concerning the physiology of the pupil, provide recommendations on how to examine data related to measurements of the pupil, and discuss psychological phenomena that modulate the reactivity of the pupil to increase or decrease its diameter.

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