Orthographic effects on vowel contrast in language acquisition

This study measures whether differing letter shapes affect the production of /ɯ/ for L1-English learners of Turkish or Korean, which use a Latin-based and featural alphabetic orthography, respectively. Native speakers and L1 English learners of Turkish and Korean were recorded reading word lists and performing a picture-naming task in their target languages to compare whether read speech is significantly different from more naturalistic speech. Acoustic analysis of the high vowels /i, ɯ, u/ (n=1056) reveals that visual similarity between Turkish <ı> and <i> causes /ɯ/ to move towards the front of the vowel space, suggesting these letters’ vertical line shape is interpreted as [+front]. The visual similarity of Korean /ɯ/~<으>, /u/~<우> and /o/~<오> results in learners analyzing /ɯ/ as having an intermediary vowel height between /u/ and /o/ rather than being contrastive via the [±round] feature. These findings demonstrate that speech production models must account for visual input, highlighting the need for further multimodal linguistic research in language acquisition.