Abstract
A crucial question in the domain of visual word recognition is whether letter similarity plays a role in the early stages of visual word processing. Here we focused on Arabic because in this language there are various groups of letters that share the same basic shape and only differ in the number/location of diacritical points. We conducted a masked priming lexical decision experiment in which a target word was preceded by: (i) an identity prime; (ii) a prime in which the critical letter was replaced by a letter with the same shape that differed in the number of diacritics (e.g., ); or (iii) a prime in which the critical letter was replaced by a letter with different shape (e.g., ). Results showed a sizable advantage of the identity condition over the two substituted-letter priming conditions (i.e., diacritical information is rapidly processed). Thus, diacritical marks play an essential role in the "feature letter" level of models of visual word recognition in Arabic.