Research using masked priming and parafoveal preview techniques has shown that visual letter similarity has an impact on word processing during the initial stages in Latin-derived scripts. However, these effects appear to be absent in Arabic. One reason for this discrepancy could be attributed to the distinctive features of the Arabic script, which includes numerous letters sharing a basic form while varying in the location or number of diacritics. To shed light on this issue, the present study employed Arabic letters rather than words in two masked priming experiments: an alphabetic decision task and a letter-matching task. Both experiments showed that visually similar letters were more effective as primes than visually dissimilar letters. These findings suggest that the processes of letter identification in Arabic and Latin scripts may be roughly alike, implying that differences in visual letter similarity across scripts may arise at later stages of processing.

Although the Latin-based orthographies of most Western languages employ vowels with accent marks (e.g., é vs. e), extant models of letter and word recognition are agnostic as to whether these accented letters and their non-accented counterparts are represented by common or separate abstract units. Recent research in French with a masked priming alphabetic decision task was interpreted as favoring the idea that accented and non-accented vowels are represented by separate abstract orthographic units (orthographic account: é↛e and e↛é; Chetail & Boursain, 2019). However, a more parsimonious explanation is that salient (accented) vowels are less perceptually similar to non-salient (non-accented) vowels than vice versa (perceptual account: e→é, but é↛e; Perea et al., 2021a; Tversky, 1977). To adjudicate between the two accounts, we conducted a masked priming alphabetic decision experiment in Catalan, a language with a complex orthography-to-phonology mapping for non-accented vowels (e.g., e→/e/, /ə/, /ε/). Results showed faster responses in the identity than in the visually similar condition for accented targets (é–É < e–É), but not for non-accented targets (e–E = é–E). Neither of the above accounts can fully capture this pattern. We propose an explanation based on the rapid activation of both orthographic and phonological codes.

Prior research has shown that word identification times to DENTIST are faster when briefly preceded by a visually similar prime (dentjst; i↔j) than when preceded by a visually dissimilar prime (dentgst). However, these effects of visual similarity do not occur in the Arabic alphabet when the critical letter differs in the diacritical signs: for the target the visually similar one-letter replaced prime (compare and is no more effective than the visually dissimilar one-letter replaced prime Here we examined whether this dissociative pattern is due to the special role of diacritics during word processing. We conducted a masked priming lexical decision experiment in Spanish using target words containing one of two consonants that only differed in the presence/absence of a diacritical sign: n and ñ. The prime-target conditions were identity, visually similar, and visually dissimilar. Results showed an advantage of the visually similar over the visually dissimilar condition for muñeca-type words (muneca-MUÑECA < museca-MUÑECA), but not for moneda-type words (moñeda-MONEDA = moseda-MONEDA). Thus, diacritical signs are salient elements that play a special role during the first moments of processing, thus constraining the interplay between the “feature” and “letter” levels in models of visual word recognition.