The shape of things to come: Evaluating word frequency as a continuous variable in recognition memory

The role of experience in memory, specifically the word frequency (WF) mirror effect showing higher hit rates and lower false alarm rates for low-frequency words, is one of the hallmarks of memory. However, this "regularity of memory" is limited because normative WF has been treated as discrete (low vs. high). We evaluate the extent to which the prototypical WF mirror effect holds when WF is treated as a continuous variable. We find a clear nonmonotonic U-shaped relationship. Hit rates are higher for both low-frequency and high-frequency words. Linear and quadratic regression models were fit to the data at both the item and the participant level, and the quadratic model provided a better fit at both levels. This finding is inconsistent with the empirical and theoretical finding of a mirror effect and requires a novel approach to accounting for the role of experience in episodic memory.