Habituation assessment in infancy

Infant-control habituation methodology, although serving the research community well, has never been carefully analyzed. A main use is to equate infants in their level of habituation prior to experimental manipulations in a posthabituation phase. When studied analytically and with simulation, it is found to have serious difficulties. It inadvertently recruits infants with large variations in performance while discriminating against those with less variable performance. For nonhabituating infants, its Type I error rates can approach 1. A model-based nonlinear regression framework is proposed, which, because of large individual differences in infants, takes as the unit of analysis the individual infant. It is shown to be more powerful and efficient than existing procedures and can offer practical and theoretical benefits.