The main focus of this dissertation is to investigate to what extent Japanese English-as-an-additional-language (EAL) learners have mastered default grapheme-phoneme correspondence (GPC) patterns of North American English vowels. The underlying motivation of this research comes from my observation that many mispronunciations of English vowels by Japanese EAL learners in formal learning settings are caused by their misinterpretation of English spellings rather than by phonological factors. Traditionally, Japanese speakers’ mispronunciations of English vowels have been attributed to a phonological factor that there is a mismatch of vowel inventories between English and Japanese. However, Nogita and Lin (2016) found that when vowel length and diphthongization are taken into consideration, native Japanese speakers are able to produce all the 13 North American English vowels although not necessarily in a native-like manner. This seems to suggest that other factors than the vowel inventory difference are responsible for the Japanese speakers EAL pronunciation errors. One such factor can be that Japanese EAL learners have not grasped the English GPC patterns and their misinterpretation of the spellings causes their pronunciation errors. To see if a GPC problem really plays a role, this dissertation examines how Japanese EAL learners map all the 13 North American English vowels with English vowel graphemes. In order to examine Japanese EAL learners’ knowledge of English vowel GPC, I conducted both reading and spelling tasks with English-like one-syllable nonsense words. In the reading task (e.g., reading aloud <snad>, <staw>, <stoe>, <nube>, etc.), the results showed that the Japanese EAL participants read vowel letters differently from native English speaking participants 40.1% of the time. In the spelling task (e.g., listening and spelling out native utterances of such syllables as [sneɪ], [zɑ:d], [gaʊ], [fʌd], etc.), the results showed that the Japanese EAL participants spelled out vowel sounds differently from native English speaking participants 60.0% of the time. These results suggest that the Japanese EAL participants’ English vowel grapheme-phoneme mapping patterns were quite different from those of the native English-speaking participants. In more details, the results showed that some correspondences were performed very well in both grapheme-to-phoneme and phoneme-to-grapheme directions presumably because of the similarities between the English GPC and the standardized Japanese romanization GPC: specifically, <e>-[ɛ] (in a closed syllable) and <oi, oy>-[ɔɪ]. In contrast, some correspondences were performed very poorly in both directions presumably in part because of the differences between the English GPC and the standardized Japanese romanization: specifically, <aw, au>-[ɑ:], <ow, ou>-[aʊ], <uh#>-[ʌ#] (# = word-final), <i>-[ɪ], and to a lesser extent <o>-[ɑ:] (in a closed syllable), and <o#, oe#, oh#>-[oʊ]. There were also correspondences that were performed very well only in the grapheme-to-phoneme direction but not in the other direction: specifically, word-medial <ee>-to-[i:] and <a_e>-to-[eɪ]. To a lesser extent, the <u>-to-[ʌ] conversion was also much less problematic than the [ʌ]-to-<u> conversion, although the <u>-[ʌ] correspondence was performed relatively poorly overall. Finally, none of the correspondences were performed very well only in the phoneme-to-grapheme direction but not in the other direction, but there were correspondences that showed this tendency. For example, the [æ: (æə)]-to-<a> conversion was much less problematic than the <a>-to-[æ: (æə)] conversion. Pedagogically, these results seem to suggest that Japanese EAL learners can benefit from being taught English default GPC patterns in order for them to improve on their graphophonic skills. / Graduate / 2017-08-23 / 0290 / 0279 / akitsugu@uvic.ca