Correcting the SIMPLE model of free recall

The scale-invariant memory, perception, and learning (SIMPLE) model developed by Brown, Neath, and Chater (2007) formalizes the theoretical idea that scale invariance is an important organizing principle across numerous cognitive domains and has made an influential contribution to the literature dealing with modeling human memory. In the context of free recall data, however, there is a previously unreported conceptual error in the specification of the SIMPLE model. We show that the error matters not only in theory but also in practice by reapplying the corrected SIMPLE model to the benchmark data reported by Murdock (1962). The corrected model makes different predictions about serial position curves, shows better fit to the Murdock (1962) data, and infers different parameters that require substantively different psychological interpretation.