Are A-not-B errors caused by a belief about object location?

Eight- to 12-month-olds might make A-not-B errors, knowing the object is in B but searching at A because of ancillary (attention, inhibitory, or motor memory) deficits, or they might genuinely believe the object is in A (conceptual deficit). This study examined how diligently infants searched for a hidden object they never found. An object was placed in A twice, and then in B. In a different task the object was placed beside A twice, and then in B. Infants made more A-not-B errors in the former task, and perseverating infants searched diligently in A rather than in B. Infants seemed to believe the object was in A, suggesting that both a conceptual deficit and ancillary deficits account for A-not-B errors.