Only a few empirical investigations have focused on infants' ability to perceive static subjective contours. Furthermore, these experiments have provided contradictory findings regarding the age at which this capability emerges. The present study examined the development of infants' sensitivity to an elliptical version of the subjective circle described by Ehrenstein. A habituation-dishabituation procedure was used to test the ability of 4-, 5-, and 7-month-old infants (N = 128) to differentiate between a subjective ellipse and a nonsubjective pattern that was constructed by displacing the inducing elements of the illusory figure. Results indicated that even the 4-month-olds were capable of discriminating between the subjective ellipse and the nonillusory display. A control experiment secured that this behavior was not generated by certain local differences between the test patterns. Furthermore, the results suggest that the perceived strength of the subjective contour was size dependent. This observation is discussed within the context of more recent neurophysiological models.
We review comparative studies of infant habituation and dishabituation performance focusing on preterm infants. Habituation refers to cognitive encoding, and dishabituation refers to discrimination and memory. If habituation and dishabituation constitute basic informationprocessing skills, and preterm infants suffer cognitive disadvantages, then preterms should show diminished habituation and dishabituation performance. Our review provides evidence that preterm infants' habituation and dishabituation are impoverished relative to term infants. On the whole, effect sizes indicated that the differences between preterms and terms are of a medium magnitude. We also find that preterms' performance is moderated by risk factors, stimulus materials, procedural variables, and age. These factors need to be taken into account in the construction of tests in which habituation-dishabituation tasks are employed. Overall, the habituation-dishabituation paradigm presents a promising approach in the diagnosis of cognitive status and development in preterm infants.
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