linguistic:voice_change, information:extraction
The responses can have a variety of causes, from an involuntary reflex reaction to exposure or inexposure to light—in low light conditions a dilated pupil lets more light into the eye—or it may indicate interest in the subject of attention or arousal, sexual stimulation, uncertainty, decision conflict, errors, physical activity or increasing cognitive load or demand. The responses correlate strongly with activity in the locus coeruleus neurotransmitter system. The pupils contract immediately before REM sleep begins. A pupillary response can be intentionally conditioned as a Pavlovian response to some stimuli.