The Role of Allograph Representations in Font-Invariant Letter Identification

The literate brain must contend with countless font variants for any given letter. How does the visual system handle such variability? One proposed solution posits stored structural descriptions of basic letter shapes that are abstract enough to deal with the many possible font variations of each letter. These font-invariant representations, referred to as allographs in this paper, while frequently posited, have seldom been empirically evaluated. The research reported here helps to address this gap with 2 experiments that examine the possible influence of allograph representations on visual letter processing. In these experiments, participants respond to pairs of letters presented in an atypical font in 2 tasks-visual similarity judgments (Experiment 1) and same/different decisions (Experiment 2). By using representational similarity analysis (RSA) in conjunction with linear mixed effect models (LMEM; RSA-LMEM) we show that the similarity structure of the responses to the atypical font is influenced by the predicted similarity structure of allograph representations even after accounting for font-specific visual shape similarity. Similarity due to symbolic (abstract) identity, name, and motor representations of letters are also taken into account providing compelling evidence for the unique influence of allograph representations in these tasks. These results provide support for the role of allograph representations in achieving font-invariant letter identification. Public Significance Statement In everyday reading, we often encounter unfamiliar letter shapes such as when we read handwritten notes or read in a font we have not seen before. Although our brains may have never before processed these shapes we are, nonetheless, usually able to effortlessly recognize them. The research reported here is directed at furthering our understanding of how this happens. In 2 experiments, research participants made decisions regarding the visual characteristics of letters presented in a highly unusual font. We found evidence that one important part of the letter recognition process involves automatically generating mental information about the standard, canonical geometric shapes of letters. These results have implications for reading teachers and clinicians working with acquired or developmental reading impairments as understanding the types of mental representations that skilled readers use for efficient and effective letter recognition can be used to structure teachin