Lexical decisions in Persian: a test of the orthographic depth hypothesis

The orthographic depth hypothesis holds that words in scripts whose spelling-sound correspondences are entirely consistent (transparent) are recognized by computing a phonological code prior to lexical access. In contrast, the universal hypothesis holds that words in all scripts are recognized by utilizing visual orthographic information to access the mental lexicon. The present experiment examines the issue of whether orthographic-phonological transparency of Persian words affect the decision in a lexical decision task, because the orthographic depth and the universal hypothesis make different predictions. Persian script enables contrast of words reflecting extremes of orthographic opaqueness and transparency. This is because, the spelling-sound correspondences in written Persian are always consistent, but only some of the words include vowels as a fixed part of their spelling, (transparent words), whereas for other words the vowels are typically not specified (opaque words). The result of the lexical decision task found that for higher frequency words the Reaction Times (RTs), were as fast for both opaque and transparent words, although RTs to lower frequency transparent words were faster than matched opaque words. These data offer support for the universal hypothesis, and are inconsistent with the orthographic depth hypothesis.