Increments or decrements of light are associated with pupillary constrictions or dilations, respectively. This was not the case when the pictures were successfully suppressed from awareness, demonstrating that pupil size is highly sensitive to the contents of consciousness.

Results revealed that when participants were aware of the sun pictures their pupils constricted relative to the control stimuli. A stream of Mondrian patterns was displayed to the right eye to produce continuous flash suppression, which rendered the left-eye stimuli invisible on some trials. Is conscious appraisal of these stimuli necessary for the pupillary constriction to occur? Participants' pupil diameter was recorded while sun pictures and their phase-scrambled versions were shown to the left eye. For example, stimuli that evoke the idea of brightness (e.g., pictures of the sun) induce pupillary constriction compared to control stimuli of matched luminance.

3Institute of Neuroscience, Consiglio Nazionale delle Ricerche (CNR), Pisa, ItalyĪlthough retinal illumination is the main determinant of pupil size, evidence indicates that extra-retinal factors, including attention and contextual information, also modulate the pupillary response.

2Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy.1The School of Psychology, University of East Anglia, Norwich, United Kingdom.Irene Sperandio 1 * Nikki Bond 1 Paola Binda 2,3

Pupil size chart for drugs