Gender and age differences in sub-phonemic variants of /o/ in Korean spontaneous speech: A corpus-based study

The purpose of this corpus-based study is to identify sub-phonemic variants of /o/ in standard Korean, focusing on phonetic variants [o] and [u] of the phoneme /o/. The major concerns of this paper are (1) substitution rates in word-final position, whereby the mid-back vowel [o] is substituted by the high-back vowel [u], and (2) the acoustic analysis of F1 and F2 (Hz) values for [o] and [u] according to gender and age differences. A total of 40 participants’ speech samples (five females and five males in each of four age groups: teens, 20s, 30s, and 40s) were selected from the Korean Corpus of Spontaneous Speech. As a result, the study confirmed the following: Although the [u] substitution rates of older female speakers were significantly higher than those of male younger speakers, younger female speakers reported a relatively shorter Euclidean distance than older male speakers. Once younger speakers substitute [u] for [o], the Euclidean distances between [o] and [u] are much closer than in older speakers; this finding is consistent with previous studies’ findings. What is noteworthy about this acoustic analysis is that statistically significant differences were found in F2 values in both male and female groups, but not in F1 values. This study also suggests that the phonetic spaces of [o] and [u] is getting closer in terms of F2 values (within 1 standard deviation) with a decrease in the ages of both men and women, which can be robust evidence that /o/-shift is still ongoing in a different direction, and might lead to another chain shift triggered by [o] moving inwards that results in high-back vowel [u] pushing in modern Korean.