Alphabetic letter identification: Effects of perceivability, similarity, and bias

Abstract

The legibility of the letters in the Latin alphabet has been measured numerous times since the beginning of experimental psychology. To identify the theoretical mechanisms attributed to letter identification, we report a comprehensive review of literature, spanning more than a century. This review revealed that identification accuracy has frequently been attributed to a subset of three common sources: perceivability, bias, and similarity. However, simultaneous estimates of these values have rarely (if ever) been performed. We present the results of two new experiments which allow for the simultaneous estimation of these factors, and examine how the shape of a visual mask impacts each of them, as inferred through a new statistical model. Results showed that the shape and identity of the mask impacted the inferred perceivability, bias, and similarity space of a letter set, but that there were aspects of similarity that were robust to the choice of mask. The results illustrate how the psychological concepts of perceivability, bias, and similarity can be estimated simultaneously, and how each make powerful contributions to visual letter identification.

A letter visual-similarity matrix for Latin-based alphabets

“…Although many letter visual-similarity matrices have been published over the last century (for a review, see Mueller & Weidemann, 2012), these can only be used to carry out relevant research in English. Furthermore, these matrices have mostly been formed from data generated in atypical reading conditions, using, for example, speeded naming or degraded presentation conditions.…”

“…For these reasons, the letter visualsimilarity matrices published to date are of limited utility for research undertaken in alphabetical languages other than English, and are also unsuitable for reading researchers who are typically interested in the mental processes occurring in natural reading conditions. The aim of the present article was to Mueller and Weidemann (2012) study were based on the predicted accuracy scores of their best model, which is described by the parameters contained in their Table 5 (Mueller & Weidemann, 2012, p. 31). The scores represent the predicted probability of a participant accurately identifying a target letter (L1) in the presence of a foil letter (L2).…”

“…In an extensive review of the literature spanning over 120 years, Mueller and Weidemann (2012) identified more than 70 published articles that had in one way or another sought to measure letter similarity (or confusability). From this review, the authors identified three main motivations for studying letter similarity: (1) practical attempts to make written text more comprehensible, and thereby allow learners to acquire reading skill more easily; (2) empirical investigations with the goal of understanding how the visual system functions; and (3) theoretical research attempting to explain how letters are represented by the visual system or, in abstract form, by the cognitive system.…”

“…To investigate how our matrix differs from those constructed using different paradigms, we compared our matrix to matrices based on (a) direct ratings of letter pair similarities (i.e., a similar paradigm as the one used in the present study; Boles & Clifford, 1989); (b) feature analysis of letter forms (i.e., nonbehavioral data; Briggs & Hocevar, 1975); (c) low contrast/noisy presentation of letters (Liu & Arditi, 2001); (d) brief presentation of letters (Mueller & Weidemann, 2012); and (e) presentation of small letters (Phillips et al, 1983). The results are summarized in Table 2.…”

“…As a result, many variations have been introduced to this paradigm so that errors will occur frequently. These include using brief presentations of the letters (Mueller & Weidemann, 2012), reducing the letter Electronic supplementary material The online version of this article …”