Pupillometry

Pupillometry is the measurement of changes in pupil size in response to cognitive, emotional, or perceptual stimuli. The pupil automatically dilates (mydriasis) during mental effort, emotional arousal, or approach-related states, and constricts (miosis) during relaxation or withdrawal. First documented systematically by Hess in the 1960s, pupillometry provides an objective, continuous measure of cognitive load, attention, and emotional response that complements behavioral and self-report measures.