Distinct orthography boosts morphophonological discrimination: Vowel raising in Bengali verb inflections

This study is concerned with how vowel alternation, in combination with and without orthographic reflection of the vowel change, affects lexical access and the discrimination of morphologically related forms. Bengali inflected verb forms provide an ideal test case, since present tense verb forms undergo phonologically conditioned, predictable vowel raising. The mid-to-high alternations, but not the low-to-mid ones, are represented in the orthography. This results in three different cases: items with no change (NoDiff), items with a phonological change not represented in the orthography (PronDiff) and items for which both phonology and orthography change (OrthPronDiff). To determine whether these three cases differ in terms of lexical access and discrimination, we conducted two experiments. Experiment 1 was a cross-modal lexical decision task with auditory primes (1 ^st PERSON and 3 ^rd PERSON forms, e.g. [lek ^he] or [lik ^hi]) and visual targets (verbal noun; e.g. [lek ^ha]). Experiment 2 uses eye tracking in a fragment completion task, in which auditory fragments (first syllable of 1 ^st or 3 ^rd PERSON form, e.g. [le-] from [lek ^he]) were to be matched to one of two visual targets (full 1 ^st and 3 ^rd PERSON forms, [lek ^he] vs. [lik ^hi] in Bengali script). While the lexical decision task, a global measure of lexical access, did not show a difference between the cases, the eye-tracking experiment revealed effects of both phonology and orthography. Discrimination accuracy in the OrthPronDiff condition (vowel alternation represented in the orthography) was high. In the PronDiff condition, where phonologically differing forms are represented by the same graphemes, manual responses were at chance, although eye movements revealed that match and non-match were discriminated. Thus, our results indicate that phonological alternations which are not represented in spelling are difficult to process, whereas having orthographically distinct forms boosts discrimination performance, implying orthographically influenced mental phonological representations.