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Pupillometry is the measurement of pupil diameter in psychology. As mentioned in the paper of Laeng et al., this method established itself after its use in three seminal studies (Hess & Polt, 1960, 1964; Kahneman & Beatty, 1966). The method examines not only humans (including infants) but also animals. Pupillary responses occur from birth and are involuntary. Pupil dilation of 0.5 mm can occur when elicited by psychological stimuli.
The beginning of pupillometry
Hess and Polt (1960) presented pictures of semi-naked adults and babies to adults (four men and two women). Pupils of both sexes dilated after seeing pictures of people of the opposite sex. In females, the difference in pupillary sizes occurred also after seeing pictures of babies and mothers with babies. This examination showed that pupils react not only to the changes of intensity of light (pupillary light reflex) but also in reaction to arousal or emotions. According to T.M. Simms (1967), pupillary responses of males and females were greater when they were exposed to pictures of the opposite sex. In another study, Nunnally and colleagues (1967) found that seeing slides rated as 'very pleasant' is associated with greater pupil dilation as seeing slides rated as neutral or very unpleasant.
Sex and pupillary response
In 1965 Hess, Seltzer and Shlien examined pupillary responses in heterosexual and homosexual males. Results showed a greater pupil dilation to pictures of the opposite sex for heterosexuals and to pictures of the same sex for homosexuals .
Pupillary responses can reflect activation of the brain allocated to resolving cognitive tasks. It is found that greater pupil dilation is associated with increased processing in the brain. Vacchiaco and colleagues (1968) found that pupillary responses were associated with visual exposure to words with high, neutral or low value. Presented low-value words were associated with dilation, and high-value words with constriction of a pupil. In decision making tasks it was found that dilation of the pupil was increased before making a decision as a function of cognitive load. In an experiment about short-term serial memory, students heard strings of items and were asked to repeat them. Greater pupillary diameter was observed after the items were heard (pupillary diameter depended on how many items were heard), and accordingly pupillary diameter decreased after items were repeated by the participants. The more difficult the task given to participants, the greater pupillary diameter observed in the time preceding the solution, and pupil dilatation is maintained until the solution is found.
Differences in pupillary diameter were also found in the domain of prefential looking in infants. Infants showed greater pupillary size when they saw pictures of faces than when they saw geometric shapes, and greater pupillary dilation after seeing pictures of the infant's mother than pictures of a stranger.
The pupil response has also been linked to long-term memory processes both at encoding, predicting the success of memory formation, and at retrieval reflecting the operation of different recognition outcomes.
- Laeng B., Sirois S., Gredebäck G. (2012) "Pupillometry: A Window to the Preconscious?" Perspectives on Psychological Science January 2012 vol. 7 no. 1 18-27
- Hess E. H., Polt J. M. (1960) "Pupil size as related to interest value of visual stimuli" Science, 132, 349-350.
- Simms T. M. (1967) "Pupillary response of male and female subjects to pupillary difference in male and female picture stimuli" Perception and Psychophysics, 2, 553-555.
- Goldwater B. C. (1972) "Psychological significance of pupillary movements" Psychological Bulletin 77(5):340-55.
- Nunally J. C., Knott P. D., Duchnowski A., Parker R. (1967) "Pupillary response as a general measure of activation." Perception and Psychophysics, 2, 149-155
- Hess E. H., Seltzer A. L., Shlien J.M. (1965) "Pupil response of hetero- and homosexual males to pictures of men and women: A pilot study" Journal of Abnormal Psychology, 70, 165-168
- Granholm E., Steinhauer S. R. (2004) "Pupillometric measures of cognitive and emotional processes" International Journal of Psychophysiology, Vol 52(1), 1-6. 
- Vacchiano R. B., Strauss P. S., Ryan S., Hochman L. (1968) "Pupillary response to value-lined words" Perceptual and Motor Skills, 27, 207-210.
- Simpson H. M., Hale S. M., (1969) "Pupillary Changes During a Decision-Making Task" Perceptual and Motor Skills, 29, 495-498.
- Kahneman D., Beatty J. (1967) "Pupillary Response in a Pitch Discrimination Task" Perception and Psychophysics, 2, 101-105.
- Kahneman D., Beatty J. (1966) "Pupil Diameter and Load on Memory" Science, 154, 1583-1585.
- Hess E. H., Polt J. H. (1964) "Pupil Size in Relation to Mental Activity During Simple Problem Solving" Science, 143, 1190-1192
- Bradshaw J. L. (1968), "Pupil size and problem solving" Quarterly Journal of Experimental Psychology, Volume 20, Issue 2, 116-122.
- Fitzgerald H. E. (1968), "Autonomic pupillary reflex activity during early infancy and its relation to social and nonsocial visual stimuli" Journal of Experimental Child Psychology, 6, 470-482
- Fitzgerald H. E., Lintz L. M., Brackbill Y., Adams G. (1967), "Time perception and conditioning an autonomic response in human infants" Perceptual and Motor Skills, 24, 479-486
- Kafkas, A., & Montaldi, D. (2011). Recognition memory strength is predicted by pupillary responses at encoding while fixation patterns distinguish recollection from familiarity. The Quarterly Journal of Experimental Psychology, 64(10), 1971–1989. http://www.tandfonline.com/doi/abs/10.1080/17470218.2011.588335
- Kafkas, A., & Montaldi, D. (2012). Familiarity and recollection produce distinct eye movement and pupil and medial temporal lobe responses when memory strength is matched. Neuropsychologia, 50(13), 3080–93. doi:10.1016/j.neuropsychologia.2012.08.001
- Tryon, W. W. (1975), "Pupillometry: A Survey of Sources of Variation" Psychophysiology, 12: 90–93. 
- Verney, S. P., Granholm, E. and Dionisio, D. P. (2001), "Pupillary responses and processing resources on the visual backward masking task" Psychophysiology, 38: 76–83. 
- Beatty J. (1977), "Pupillometric Measurement of Cognitive Workload"