The A-not-B error (Piaget, 1954) , which occurs when infants search perseveratively on reversal trials in a delayed-response task, is one of the most widely studied phenomena in developmental psychology. Nonetheless, the effect of A-trial experience on the probability and magnitude of this error remains unclear. In this study, 9-month-old infants were tested at location A until they searched correctly on 1, 6, or 11 A trials. Results revealed an effect of A trials on the proportion of infants

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... o erred on the first B trial, and on the number of errors prior to a correct search at B (i.e., the error run). These effects were asymptotic, or U-shaped, consistent with a dual-process model according to which A-trial experience increases habit strength but also provides opportunities for reflection on task structure.