When people repeatedly perform the same cognitive task, their mean response times (RTs) invariably decrease. The mathematical function that best describes this decrease has been the subject of intense debate. Here we seek a deeper understanding of the effect of practice by simultaneously taking into account the changes in accuracy and in RT distributions, both for correct and error responses. To this end we used the Ratcliff diffusion model, a successful model of two–choice RT that decomposes the effect of practice into its constituent psychological processes. Analyses of data from a 10,000–trial lexical decision task demonstrate that practice not only affects speed of information processing, but also response caution, response bias, and peripheral processing time. We conclude that the practice effect consists of multiple subcomponents, and that it may be hazardous to abstract the interactive combination of these subcomponents in terms of a single output measure such as mean RT for correct responses.
Supplementary materials may be downloaded from www.psychonomic.org/archive.