Optimal Policies for Free Recall

There is rich structure in the order in which studied material is recalled in a free recall task (Howard & Kahana, 2002a). Extensive effort has been directed at understanding the processes and representations that give rise to this structure; however, it remains unclear why certain types of recall organization might be favored in the first place. We provide a rational analysis of the free recall task, deriving the optimal policy for recalling items under the internal representations and processes described by the context maintenance and retrieval (CMR) model of memory search (Polyn et al., 2009a). Our model, which we call rational-CMR, shows that the optimal policy for free recall is to start from the beginning of the list and then sequentially recall forwards, providing a rational account of the primacy and forward asymmetry effects typically observed in free recall. In addition, when recall is not initiated from the beginning of list, it is optimal during recall transitions to minimize the amount of forward asymmetry. Predictions from the rational model are confirmed in human behavioral data: Top-performing human participants demonstrate a stronger tendency to initiate recall from the beginning of the list and carry forward recalls, and the amount of forward asymmetry in participants depends on whether they start recall from the beginning or end of the list. We discuss the resemblance of optimal behavior in free recall to participants' behavior when applying mnemonic techniques such as the method of loci.