The pupil dilation response to visual detection

The pupil dilation reflex is mediated by inhibition of the parasympathetic Edinger-Westphal oculomotor complex and sympathetic activity. It has long been documented that emotional and sensory events elicit a pupillary reflex dilation. Is the pupil response a reliable marker of a visual detection event? In two experiments where viewers were asked to report the presence of a visual target during rapid serial visual presentation (RSVP), pupil dilation was significantly associated with target detection. The amplitude of the dilation depended on the frequency of targets and the time of the detection. Larger dilations were associated with trials having fewer targets and with targets viewed earlier during the trial. We also found that dilation was strongly influenced by the visual task.