The diacritical markers that represent most of the vowels in the Arabic orthography are generally omitted from written texts. Previous research revealed that the absence of diacritics reduces reading comprehension performance even by skilled readers of Arabic. One possible explanation is that many Arabic words become ambiguous when diacritics are missing. Words of this kind are known as heterophonic homographs and are associated with at least two different pronunciations and meanings when written without diacritics. The aim of the two experiments reported in this study was to investigate whether the presence of diacritics improves the comprehension of all written words, or whether the effects are confined to heterophonic homographs. In Experiment 1, adult readers of Arabic were asked to decide whether written words had a living meaning. The materials included heterophonic homographs that had one living and one non-living meaning. Results showed that diacritics significantly increased the accuracy of semantic decisions about ambiguous words but had no effect on the accuracy of decisions about unambiguous words. Consistent results were observed in Experiment 2 where the materials comprised sentences rather than single words. Overall, the findings suggest that diacritics improve the comprehension of heterophonic homographs by facilitating access to semantic representations that would otherwise be difficult to access from print.

The diacritical markers that represent most of the vowels in the Arabic orthography are typically omitted from written texts, thereby making many Arabic words phonologically and semantically ambiguous. Such words are known as heterophonic homographs and are associated with different pronunciations and meanings. The three experiments reported in this paper were conducted to investigate how Arabic readers understand diacritized heterophonic homographs.The results suggested that even when diacritics were added to disambiguate a heterophonic homograph, it was still initially processed as if it was ambiguous and its alternative meaning(s) were activated.