Two storage mechanisms in free recall

Two experiments were carried out to test the hypothesis that the bimodal serial position curve in free recall is produced by output from two storage mechanisms—short-term and long-term. Experimental operations were applied that were predicted to have a distinct effect on each of these mechanisms, and the changes in the serial position curve were observed. In the first experiment, presentation rate and repetition of individual words were varied in order to affect long-term storage and thereby affect the beginning sections of the serial position curve. Presentation rate has the predicted effect of differentially raising the beginning section of the serial position curve. It does not affect the end section. Repetition, however, did not have any effect that could not be ascribed to presentation rate. It could not, therefore, be used to demonstrate independently the predicted differential effect. In the second experiment, delay between end of list and recall was varied in order to affect short-term storage and, thereby, the end section of the serial position curve. The predicted effect was clearly demonstrated. The results make it possible to systematize a number of findings in the literature.