Diameter of the pupil of the human eyedoes not only change in response to variations in ambient light (pupillary light reflex), but it additionally responds to the perception of arousing oremotionally relevant stimuli and to the increased cognitive load caused bymemory demands (e.g., by increasing the span of a string of digits to be remembered),or the difficulty of mental calculations. Pupillometry makes use of this effectby using the pupil diameter as dependent variable to measure infants’ (andadults’) processing of observed stimuli and events. The technique has proved to be useful in screening for a number of disorder (e.g., diabetes). In studying infants, it is valuable with regard to cognitive development as it provides a time course of how an infant responds to novelty, but it is not without some methodological problems that are amenable to resolution (see Hepach & Westerman, 2013).
See Novelty preference, Oculomotor nucleus, Violation of expectation technique
Hepach, R., & Westermann, G. (2013).Pupillometry in infancy research. Journal of Cognition and Development, 17, 359-377.