Categorical and gradient effects in segmental deletion:
the case study of /w/-deletion in Seoul Korean
Introduction In Seoul Korean, /w/ is variably deleted after a consonant (e.g. sa.kwa→sa.ka ‘apple’)and /w/-deletion is constrained by various linguistic and social factors (Silva, 1991; Kang, 1997;Kwon, 2016). /w/-deletion has been regarded as a categorical alternation of /w/ and zero only, hence
the phonetic variability of /w/ has rarely been discussed in the literature. This study examines theeffects of categoricity and gradiency on /w/-realization, using articulatory data.
Methods Three female speakers participated in the ultrasound recording. Midsagittal images of thetongue were recorded using the EchoB ultrasound machine with a 5-8 MHz convex-curved
transducer (87fps for 70mm depth; 70% FOV). Also, the side-view video of the participants’ face wasvideotaped to record lip rounding. The speakers participated in the semantic differential task ofexplaining the difference between 14 minimal pairs of words containing CV and CwV sequence (e.g.
tweji ‘pig’ vs. teji ‘earth’), which elicited 465 tokens. To quantify the amount of movement ofarticulators, Optical Flow Analysis (OFA), a video-based motion analysis tool measuring themagnitude of movement (MM) of two articulators, lips and tongue (Barbosa et al., 2008), was used.
Mixed-effects regression models were fit to the normalized values of MM to examine the effects ofDURATION and CATEGORY (CwV vs. CV).
Results & discussion Several mixed effects models
were constructed for the magnitude of lip and tongue
gestures, respectively, and compared to each other interms of their goodness-of-fit. For lip gestures, themodel including DURATION and CATEGORY
together with their interaction provides the best fit.
Based on this model, CATEGORY has significant maineffects (p<0.001); and more importantly, there is asignificant interaction between CATEGORY andDURATION (p<0.01). Once the interaction is added,
the sole effect of DURATION generates a nonsignificant p-value, highlighting how duration plays a bigger role in conditioning CwV than CV. In
Figure 1, the correlation lines for CV and CwV diverge from each other, indicating a significant effectof CATEGORY. CwV exhibits a strong positive correlation between the magnitude of lip gesturesand duration, with a Pearson’s value of r=0.699 (p<0.001) while CV has a much weaker but significant
value of r=0.375 (p<0.001). The amount of gestures for CwV is much more strongly correlated withduration than that of CV, which suggests that /w/ exhibits a wide range of temporal and gesturalvariability. The categorical distinction between CwV and CV is mediated by the gradient factor –DURATION: the longer the duration, the more robust the categorical distinction between the two.
For tongue gestures, by contrast, both CwV and CV show a strong correlation with duration and do
not show much difference from each other: tongue's contribution to making acoustic and perceptual
cues for /w/ in Seoul Korean appears minimal. The findings demonstrate that the realization of /w/deletion in Korean is subject to gradient phonetic effects as well as effects of category. The results arediscussed in terms of how phonological processes evolves diachronically discussed (Bermudez-Otero
2015; Kiparsky 1995). This study also provides important methodological implications for researchanalyzing phenomena understood only as categorical processes.

References
Bermúdez-Otero, R. (2015). Amphichronic explanation and the life cycle of phonological processes.
In The Oxford handbook of historical phonology (pp. 374-399). Oxford University Press.
Kiparsky, P. (1995). The phonological basis of sound change. The Handbook of Phonological Theory,edited by John Goldsmith.