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Pupil Dilation and Object Permanence in Infants


should be sent to Sylvain Sirois, Département de Psychologie, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, Qc, Canada G9A 5H7. E-mail:


This paper examines the relative merits of looking time and pupil diameter measures in the study of early cognitive abilities of infants. Ten-month-old infants took part in a modified version of the classic drawbridge experiment used to study object permanence (Baillargeon, Spelke, & Wasserman, 1985). The study involved a factorial design where angle of rotation and presence or absence of an object were crossed. Looking time results are consistent with previous work and could suggest object permanence if one ignored data from all cells of the factorial design. When all cells are considered, the data rather suggest a perceptual interpretation. Dynamic changes in pupil diameter uniquely support this interpretation, illustrating which aspects of events (and when) infants primarily respond to. Overall, the results fail to support object permanence in 10-month-olds, and pupil dilation provides a much finer-grained interpretation of infants’ information processing, relative to looking time.