Orthographic uncertainty

Abstract Measures of orthographic typicality have long been studied as predictors of lexical access. The best-known orthographic typicality measure is orthographic neighbourhood size ( Coltheart’s N or ON ), the number of words that are one letter different, by substitution, from the target word. A more recent related measure of orthographic typicality is orthographic Levenshtein distance 20 ( OLD20 ), the average Levenshtein orthographic edit distance of a target word from its 20 closest neighbours ( Yarkoni, Balota, and Yap, 2008 ). Both measures have been implicated in lexical access. In this paper, we propose and assess a family of measures of word form similarity we call orthographic uncertainty . These measures are based on Shannon entropy ( Shannon, 1948 ), which has a long history of being considered psychologically relevant. Orthographic uncertainty measures are superior to ON and OLD20 at predicting lexical decision and naming reaction times and accuracies. They are also superior to the older measures insofar as they are naturally tied to the widely-accepted quantification using Shannon Entropy of the psychological functions of familiarity, uncertainty, learnability, and representational and computational efficiency.