Context effects in letter perception : a comparison of two theories

Abstract: "The purpose of this study is to test whether EPAM (Elementary Perceiver and Memorizer) can explain context effects in letter recognition. EPAM, a model of learning and recognition in the form of a computer program, has successfully explained many aspects of learning and perception in a range of task environments. In 1984, Barsalou and Bower claimed that EPAM could not explain the phenomena in the tachistoscopic perception experiments successfully simulated by the Interactive Activiation Model (IAM) of word perception (McClelland & Rumelhart, 1981; Rumelhart & McClelland, 1982).In this study, using EPAM IV, a revision of the most recent version of EPAM, we show that the human data modeled by the IAM are at least as accurately simulated by EPAM. Close examination of the performance of the two programs shows that the fact that one (EPAM) processes perceptions serially, while the other (IAM) processes them in parallel, plays no essential role in producing the context effects that are observed. The main effects are produced, in both programs, by a feedback of information from word recognition to the process of recognizing letters."