The Vowelization Effect in Arabic Reading: A Systematic Review and the Conditional Facilitation Account

The results of studies on Arabic vowelization have been mixed: some have shown that diacritical marks facilitate reading, while others document processing costs. These discrepancies suggest that vowelization effects are not uniform but conditional on multiple interacting factors. The present systematic review synthesizes empirical studies published between 2000 and 2025 to identify the conditions under which vowelization facilitates or constrains reading. Following PRISMA guidelines, 26 studies examining native Arabic readers across different developmental stages, reader profiles, and task paradigms were included. Results indicate that vowelization effects vary across four dimensions: reader development and proficiency, task demands and outcome measures, word level properties, and the diglossic structure of Arabic. Diacritics tend to facilitate reading in the early grades, when phonological decoding is still developing and lexical representations are weak, or when target words are phonologically ambiguous. When lexical knowledge is well established, full vowelization may slow recognition without improving accuracy, possibly because the added visual information interferes with pattern-based word identification. To account for these patterns, we propose a Conditional Facilitation Account (CFA), which treats vowelization effects as a function of the interaction among reader proficiency, lexical properties, task demands, and the sociolinguistic context of Arabic. The CFA has implications for reading theory and for decisions about vowelization in Arabic educational materials.