The letter-frequency effect and the generality of familiarity effects on perception

A widely accepted perceptual principle is that familiar patterns are easier to recognize than are less familiar patterns. Previous letter-recognition studies are examined to determine whethermore frequent letters in English are easier to recognize than less frequent letters (the letterfrequency effect). Most studies required subjects to identify single letters, while some measured reaction time to compare two letters or name or classify a letter. The results, based on over 800, 000 observations from 58 studies that span nearly 100 years, showed that: (1) there is no letter-frequency effect in recognition studies in which subjects simply report letters, and (2) there is a letter-frequency effect in reaction time studies. The presence of la letter-frequency effect for reaction time studies is interpreted as demonstrating an effect of familiarity on a comparison stage and perhaps a response stage, but not on input coding. The absence of a letter-frequency effect for single-letter recognition studies is interpreted as limiting the generality of the effect of familiarity on perception and as limiting the generality of models that correctly predict frequency effects for words. Alternative explanations for the absence of a letter-frequency effect are discussed.