Pupillometry

Pupillometry is the measurement of pupil size and its dynamic changes over time. It is commonly performed with infrared video-oculography or dedicated eye-tracking systems that record pupil diameter at high sampling rates. Pupil size reflects autonomic nervous system activity and is modulated by luminance, cognitive effort, emotional arousal, and attention.

Typical data include baseline pupil diameter, task-evoked pupil responses, and metrics such as peak dilation, dilation latency, and rate of change. Because luminance strongly drives pupil size, experiments control lighting and equalize stimulus luminance or use isoluminant stimuli. Data are preprocessed to remove blinks, interpolate missing values, and smooth trajectories; baseline correction is often applied to obtain relative dilations.

Hardware ranges from low-cost palm-sized trackers to high-end laboratory systems, with sampling rates from tens to thousands of Hz. Experimental design often includes control of gaze position, accommodation, and refractive error. The pupillary response is thought to index locus coeruleus activity linked to surprise, attention, and effort, though interpretation is indirect and context dependent.

Applications span cognitive psychology, neuroscience, and clinical research. Pupillometry has been used to study reading, memory load, decision making, and emotional processing. In clinical contexts it supports assessment of autonomic function, medication effects, and disorders with altered arousal systems. Limitations include sensitivity to lighting changes, pupil disorders, medications, age, iris color, and individual baseline variability; cross-study comparability requires standardized protocols.