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 aim of the six experiments reported in this thesis is to investigate how proficient readers of Arabic process diacritics, and how they understand heterophonic homographs with and without diacritics. In Experiment 1, readers were asked about the meaning of ambiguous and unambiguous words presented with and without diacritics. Results showed that diacritics improved the comprehension of ambiguous words (i.e., heterophonic homographs) without impacting their speed, but that they had no effect on the comprehension of unambiguous words while slowing them. Consistent results were observed in Experiment 2 where the materials comprised sentences rather than single words. Therefore, diacritics were found to improve reading comprehension by facilitating access to the semantic representations of heterophonic homographs that would otherwise be difficult to access from print. In Experiment 3, only the heterophonic homographs were diacritized in a sentence, in order to determine whether this selective diacritization might appear the most economic way to use diacritics. Even if mixed, the results suggested that adding diacritics to the whole sentence or to the heterophonic homograph only improved the comprehension of sentences equally. The results did not clearly provide evidence that selectively diacritizing the heterophonic homograph was optimal for reading comprehension. The last three experiments were conducted to further 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 processed as if it was ambiguous and both of its meanings were activated
