The A-not-B error is one of the most robust and highly studied phenomena in developmental psychology. The traditional Piagetian interpretation is that the error reflects the immaturity of infants' understanding of objects as permanent entities. More recently, the error has been interpreted in terms of changes in representation, in memory, in spatial knowledge, and in inhibitory processes. Each account may be partially right but none offers a unified account of the many accumulated facts about this error. This article presents and tests a new unified explanation. The authors propose that the perseverative reach back to A is the product of the processes that take a hand to a location in visual space: the body-centered nature of the spatial code, memories for previous reaching activity, and the close coupling of looking and reaching. The results from 6 experiments support this explanation. The results are used to challenge the idea of knowledge independent of and distinct from behavior.

Two experiments investigated the proposition of the elaboration explanation for contextual interference that more than one task is present in working memory when multiple tasks are practiced in a random schedule but that only one task is present in working memory when multiple tasks are practiced in a blocked schedule. Three motor tasks were performed as fast as possible in either a random or blocked practice schedule. At the end of practice, a reminder trial for each task was either given or not given. Acquisition performance was slower for the random practice conditions than for the blocked practice conditions. Retention performance was faster for the random practice conditions than for the blocked practice condition that did not receive a reminder trial for each task. Importantly, performance differences were not found between the random practice conditions and the blocked practice condition that did receive a reminder trial for each task. A blocked practice condition with a beneficial acquisition and reminder task order pairing performed faster during both acquisition and retention than a comparable random practice condition. Reminder trials can facilitate detailing of task characteristics, and their effectiveness is determined by the elapsed time and number of intervening tasks during acquisition and retention.

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