How lexical decision is affected by recent experience: symmetric versus asymmetric frequency-blocking effects

In a lexical decision task (LDT) in which list composition is manipulated, a typical finding to date has been a slowdown for easy items (e.g., high-frequency words) but little speedup for hard items (e.g., low-frequency words) when they are mixed together. This asymmetric frequency-blocking effect contrasts with the symmetric pattern (both a speedup for hard items and a slowdown for easy items when they are mixed together) observed with the naming task. In the present study, we investigated the mechanism responsible for the asymmetric blocking effect in the LDT within a model of blocking effect proposed by Mozer, Kinoshita, and Davis (2003), termed the adaptation-to-the-statistics-of-the-environment (ASE) model. Experiments 1A and 1B showed that when the same high- and low-frequency words were used, consistent with the existing literature, an asymmetric blocking effect was found in the LDT and a symmetric blocking effect was found in the naming task. Within the ASE model, a symmetric versus asymmetric blocking effect can be explained in terms of different asymptotic rates in subjective estimates of error probability. Experiments 2 and 3 tested and confirmed a prediction of the model based on this assumption that a speedup of hard items would be observed in an LDT with hard items whose subjective error probability asymptotes near zero (low-frequency words with high familiarity ratings that subjects could be certain were words). Implications of the model for task differences in reaction times are discussed.