Regional accents that differ from those of listeners impede higher levels of language processing, much as the processing words in foreign-accented speech can be more effortful and error-ridden than in native accents (Arnhold et al., 2020; Floccia et al., 2009). The present study explores the acoustic predictors of perceived regional accent, based on the understudied North Korean (NK) dialect produced by NK refugees residing in the Seoul metropolitan area. Although North and standard Seoul South Korean (SK) dialects are mutually intelligible, linguistic divergence has been observed in phonology, morphology, grammar, pragmatics, and most noticeably, in the lexicon, mainly because North and South Korea have used different language policies since their separation after the Korean War. North Korea banned the use of Chinese characters and prohibited the influx of loanwords in terms of nativizing them, whereas South Korea was open to non-native words, actively accepting foreign and loan words, both Sino-Korean and Indo-European (Choi, 2025; Lee, 2022; Sohn, 2001). The geo-political separation and different language policies led SK and NK that were originally the same to experience linguistic divergence, and today, the North Korea and South Korea are considered two different countries. After 1990, many North Koreans moved to the South because of severe poverty. As of March 2025, there were a total of 34,352 refugees from NK living in South Korea (The Ministry of Unification in Korea). Upon arrival, the refugees attend an adaptation program supported by the SK government to learn about the culture, language, and career paths in South Korea. As most NK refugees are stigmatized because of their economic status, many attempt to adapt to the SK community by hiding their NK identity and language (Kang and Yun, 2018).

The main goal of the present study was to identify the sources of the primary acoustic characteristics of NK dialect accents. Since we are exposed to a variety of NK dialects in SK society, not just one particular dialect, we explored the acoustic sources of the perceived NK dialect accents produced by NK speakers from different backgrounds. For this purpose, we used the methodology employed in previous studies on the phonetic sources of perceived foreign (L2) accents. Many studies have investigated the acoustic sources of perceived foreign accents (Anderson-Hsieh et al., 1992; Jilka, 2000; Sereno et al., 2016; Wayland, 1997). For example, Wayland (1997) examined the production of Thai vowels, consonants, and tones produced by native English speakers, focusing on which acoustic parameters influence native (L1) listeners' judgments of the perceived degree of accentedness. She found that among segments, only vowel differences in the spectral, as opposed to temporal, dimensions contributed to accentedness, indicating the larger role of vowel features than others in the rating of L2 accents. Idemaru et al. (2019, 2021) explored the acoustic sources of foreign accent in L2 Japanese produced by English and Mandarin learners. When examining segmental (vowels and stops) and suprasegmental (rhythm, tone, and fluency) features, they found one of the prosodic features (pitch accent and intonation) to be a strong predictor of foreign accent across the two L1 backgrounds, which was significantly stronger than the other prosodic features, vowels, and stops. Thus, previous studies suggest that the degree of foreign accents differs according to the sound contrast types in L1–L2 pairs.

Studies have reported that the phonetic differences between NK and SK dialect are mainly observed in segments such as vowels or consonants. First, Table 1 presents the vowel inventory of NK and SK dialects.

Before the Korean War, Korean monophthongs comprised 10 monophthongs (/i, e, ε, ʌ, ∔, o, u, a, y, ø/; Shin et al., 2013). However, most SK speakers do not retain all of the monophthongs. First, /ε/ has been raised to and neutralized with /e/ (Eychenne and Jang, 2015; Lee and Cho, 2021). For example, Eychenne and Jang (2015) have investigated the production of /e/ and /ε/ across the different regional dialects and gender groups of younger generation speakers; they found that the contrast of these two vowels was largely lost. Moreover, Kang (2014) reported that when partitioned by age and gender, the /e-ε/ contrast seems marginally retained by older male speakers (specifically those born before 1962) in word-initial position alone. Second, /y/ and /ø/ have been diphthongized to /wi/ and /wε/, respectively (Kang and Yun, 2018; Shin et al., 2013). From ~1990, in both natural and real speech, these two vowels were never produced as monophthongs. Consequently, the SK dialect has seven monophthongs. Additionally, in SK, the vowel /o/ has been raised toward /u/ (Han and Kang, 2013), which in turn led to the closeness of /u/ to /∔/ (Kang, 2014; Kang and Kong, 2016). (Han and Kang 2013) examined these two vowels' acoustic characteristics and their Euclidean distance; they observed that /o/ became increasingly approximated with /u/, particularly in younger female speakers and non-initial positions. More recently, Kang (2014)—based on the analysis of a large corpus of data—observed that the vowels /∔/ and /u/ are realized with a higher F2 (equivalent to a more front vowel quality) among younger speakers. Based on this phenomenon, she argued that the SK vowel system appears to be undergoing the chain-shift change of the three vowels /∔, u, o/.

Unlike the SK vowels, few systematic phonetic studies have examined NK vowels. Based on the results of previous empirical studies on NK refugees, the NK dialect likely maintains the 10- (Lee and Idemaru, 2024) or 8-vowel system of monophthongs, with the diphthongization of /y/ and /ø/ (Lee and Ramsey, 2000). Namely, /e/ has lower F1 values (equivalent to a higher vowel quality) than /ε/, without overlapping values. The vowel /∔/ is produced in the back region of the vowel space, close to /u/. Additionally, NK and SK dialects differ in the spectral qualities of /o/ and /ʌ/—in NK, /o/ is lower than /ʌ/, while the opposite is true in SK.

Regarding consonants, NK and SK dialects reportedly differ in their use of acoustic cues for stops. Although both dialects have a three-way contrast in stops, namely lenis, fortis, and aspirated, the primary acoustic cues used to distinguish stops differ between the two. Before the early twentieth century, stops were historically distinguished based on the duration of their Voice Onset Time (VOT; Cho et al., 2002). The VOT values of stops are the shortest for fortis, moderate for lenis, and the longest for aspirated. However, recent phonetic studies (Bang et al., 2018; Kang and Guion, 2008; Silva, 2006) have shown that the SK dialect has considerable overlap of VOT values between lenis and aspirated stops; therefore, VOT is no longer a salient cue to differentiate them. Instead, the F0 in the vowel following the stop is used as the primary cue to differentiate lenis and aspirated stops, with a lower F0 for lenis stops than for aspirated stops. As a result, the three stops in SK appear to be distinguished based on VOT and F0: a very short VOT and high F0 for fortis stops, a long VOT and low F0 for lenis stops, and a long VOT and high F0 for aspirated stops.

By contrast, the production patterns of NK stops remain largely unknown owing to the lack of systematic phonetic studies on NK consonants. However, the results of previous studies on the NK refugees living in Seoul, South Korea (Kang and Yun, 2018; Lee et al., 2025) reveal that NK speakers distinguish the three stop categories by VOT, and F0 was not utilized robustly. In Lee et al. (2025), NK refugees participated in the tasks of reading aloud one-syllable words and short phrases, as well as a sociolinguistic interview. The results indicated that NK speakers distinguished the three categories of stops by VOT in all tasks, except for the phrase reading where fortis and lenis stops were barely distinguishable, while F0 was not utilized as robustly by NK speakers as by SK speakers. Although the empirical data on NK stops have focused on the two different dialects such as the Hamgyeong (Kang and Yun, 2018) and Pyongan dialects (Lee et al., 2025), these studies suggest that NK stops are still distinguished by VOT, and that the process of acquiring the second dialect remains incomplete. This has resulted in a major discrepancy in the phonetic characteristics of stops between the NK and SK dialects.

Similar to stops, the affricates in NK and SK have a three-way contrast, such as lenis, fortis, and aspirated; however, prior studies reported that NK speakers articulate affricates in a more anterior position than do SK speakers. Although the place of articulation of affricates in SK has been variably described as “palatal,” “postalveolar,” or even “alveolar,” previous studies have demonstrated more posterior articulation of SK affricates than alveolar fricatives (/s, s'/; Anderson et al., 2004; Kang and Kochetov, 2010). More recently, Kong et al. (2014) examined young SK speakers using the spectral peak frequency as an acoustic index of the place of articulation and found gender-related variations. The constriction locations of the females' affricates were closer to or as anterior as the alveolar fricatives, while the males' affricates were still posterior to the alveolar fricatives, supporting the post-alveolar place of affricates. Therefore, they argued that this gender-specific variation in SK affricates may represent an ongoing sound change led by female speakers. By comparison, no research has investigated the place of NK affricates. Prior studies based on NK refugees residing in the Seoul metropolitan area from Northern Hamgyeong dialect (Kang and Yun, 2018) and Mandarin-Korean bilinguals using Northern Hamgyeong dialect or Pyongan dialect (Schertz et al., 2017) might provide a hint regarding the location of the NK affricates: Both groups of NK speakers produced the /tɕ/-initial words in various vowel contexts (including /i/) with higher center of gravity (COG) values than those of SK speakers. This result may indicate the NK speakers' more anterior articulation of affricates.

Unlike segments, objectively verified data are lacking on the NK dialect's prosodic characteristics. In the SK dialect, the intonation structure is hierarchically organized such that an Intonational Phrase (IP) comprises one or more Accentual Phrases (APs), which in turn can have one or more words. The AP has the primary pitch pattern of “THLH” where “T” is realized as “H” if the vowel is preceded by fortis or aspirated consonants and “L,” elsewhere. The final syllable of the IP has a boundary tone; thus, the “H” in the last syllable of “THLH” is realized as “L” or “HL” in the statement sentences, and “H” or “LH” in the interrogative sentences (Jun, 2000). For the NK dialect, Lee and Cho (2021) impressionistic descriptions stated that the AP has the primary pitch pattern of “falling” (a pattern whereby the first syllable is “H” and the last syllable is “L”; “H…L”), and in the IP, the last syllable is associated with the boundary tone, namely, “L” for the statement sentences, and “H” for the interrogative sentences. However, experimental studies have not validated these impressionistic descriptions. Considering the dearth of relevant acoustic studies on NK prosody, exactly how the pitch patterns of NK speakers' AP and IP differ from those of SK speakers and whether NK speakers' pitch patterns are associated with their perceived NK accent remains unclear. Notably, NK speakers may produce sentences exhibiting the same prosodic pattern as SK speakers, or other unknown features may emerge in their productions.

Given that NK and SK differ in these segmental and presumably suprasegmental features, this study aims to explore the potential acoustic sources of the NK accent produced by NK refugees living in the Seoul metropolitan area. Specifically, we constructed target sentences, each containing one of the phonetic features in which the two dialects were shown to exhibit discrepancies. The phonetic features included vowel formants, VOT and F0 values of stops, place cues of affricates, and intonation contours. The target sentences produced by NK refugees were then presented to and rated by SK speakers. The accent ratings enabled us to evaluate the acoustic features that contributed the most to the perceived NK accent.

The present study investigated the acoustic sources of the perceived NK dialect accent in sentences produced by NK refugees in the Seoul metropolitan area and found that not all acoustic features predicted the degree of the perceived NK accent equally. Various phonetic features were examined, such as vowel formants for the two pairs of vowels, /u-∔/ and /o-ʌ/, stop VOTs, COG of affricates, and IP-boundary tones. Consequently, spectral features of the /o-ʌ/ pair emerged as the most robust predictor of accentedness, and acoustic features differentiating the lenis and aspirated stops were the weakest predictor. The remaining acoustic features were mildly correlated with NK accent ratings.

A comparison between the results of acoustic measurements and NK dialect accent ratings revealed a match between production and perception, except for the acoustic cues used to differentiate the lenis from aspirated stops. The distribution of /o/ and /ʌ/ between the NK and SK dialects significantly contributed to the perceived NK accent. In contrast to the vowel heights in SK, the NK participants produced /o/ lower than /ʌ/. The two vowels produced by the NK participants seemed to be close together, yet they did not exhibit a reversal in their relationship, as seen in SK. This difference likely directly influenced the perceived NK accent. However, the vowel pair of /u-∔/, the COG of affricates, and the pitch patterns appeared to be largely adapted to SK. Moreover, unlike NK speakers with limited exposure to SK, whose /∔/ was close to /u/, the NK participants produced /∔/ much further forward than /u/, with no overlap between the two vowels. Similarly, NK participants produced affricates further back in the oral cavity than typical NK speakers, which is a feature of SK speakers. The intonation patterns were also similar to those of the SK dialect for most of the NK participants; however, these results should be interpreted with caution. A small percentage of the NK participants' utterances showed a pattern different from that of the SK dialect, which resulted in a perceived NK accent.

The change in the production of the first regional Korean dialect and the subsequent change in its perceived accent when moving to a new region has been well-documented in previous studies of second dialect acquisition (Clopper et al., 2023; Conn and Horesh, 2002; Johnson and Nycz, 2015; Kang, 2022; Nycz, 2016). For example, Kang (2022) examined the production of word-initial tensification and /∔-ʌ/ merger, which are features of nonstandard Gyeongsang Korean dialect, in Gyeongsang-to-Seoul and Seoul-to-Gyeongsang transplants, and found that all speakers in these two groups produced Seoul (standard) forms only. In prosody, speakers from the southwestern dialect (i.e., the Jeolla dialect) area, especially female speakers, showed a rapid adaptation to the prosodic patterns of the standard, SK dialect, suppressing the pitch patterns of their home dialect when they moved to the Seoul metropolitan area (Kang, 2015). This may be related to the social evaluation of the dialects, where speakers from the non-standard regional dialect are likely to orient toward the standard dialect, which has greater overt prestige. Migration-triggered shifts in perception have also been observed (Evans and Iverson, 2007). Considering the social status of NK refugees and their language attitudes toward the SK dialect, adaptation to SK must have been far more rapid and intensive than in other second dialect acquisitions.

An exception in the match between production and perceived accent ratings was observed in the stop VOT. In the standard SK dialect, the primary cue to the lenis-aspirated stop contrast is shifted from the VOT to the F0 of the following vowel (Kang and Guion, 2008; Lee et al., 2020). The NK participants employed F0 to distinguish between these two stop categories, indicating their adaptation to SK. However, they simultaneously retained a large VOT difference between lenis and aspirated stops. Using both acoustic cues—namely F0, used in SK, and VOT, used in NK—might have led to the lowest perceived NK accent rating. One possible explanation for the use of both acoustic cues is that the NK participants are in the process of adapting to SK by using the cues for stops; therefore, they might easily pick up the F0 cue and then slowly lose the VOT cue. This result contrasts with the previous work in which VOT and F0 were measured in NK refugees in Seoul and only VOT showed a statistically significant difference between lenis and aspirated stops (Lee et al., 2025). In this work, the use of F0 cue by NK refugees in this context approached that of SK speakers, higher F0 for aspirated than lenis stops; however, NK refugee speakers' degree of differentiation of these two stops by F0 did not reach the level of SK speakers. The discrepancy between these results may be due to the difference in the length of residence in South Korea; in Lee et al. (2025), the NK refugees averaged 3.7 years (SD = 3.4) of residency at the time of experiment, while in the present study they averaged 13.78 years (SD = 4.6).

Relatedly, Lee et al. (2024) investigated the acoustic cue weighting of the Korean lenis-aspirated contrast in the perception and production of mobile speakers from Gyeongsang to the Seoul dialect region. The change in cue weighting in the standard Seoul dialect from VOT to F0 was observed more clearly in the use of the innovative F0 cue than in the abandonment of the conservative VOT cue, more salient for perception than for production. Furthermore, this trend was more robust for female than male speakers. Mobile speakers used F0 in the same way as Seoul speakers in both perception and production, whereas in the use of VOT, mobile speakers were similar to Seoul speakers in perception but more like their home dialect speakers in production. These results suggest that mobile speakers use the primary cue F0, which is required to be intelligible in SK, and continue to use the conservative VOT cue simultaneously. Lee et al. (2024) interpret this as an attempt to maintain the home dialect's identity in a new speech community. The retention of the VOT cue by NK refugees can be explained similarly. The NK refugees quickly acquired the Seoul dialect, but at the same time they revealed a subconscious desire to preserve their NK identity because it could be a way to maintain a connection to the home dialect.

The /o-ʌ/ pair was the most robust predictor of accentedness in this study. If the NK speakers produced the vowels /o-ʌ/ as typical NK dialect speakers, it would result in a strong NK dialect accent and threaten a phonological contrast, thus eliciting confusion regarding the lexical items that contained the two vowels. Recall that the vowels /o/ and /ʌ/ are in a completely inverse relationship between NK and SK regarding vowel height; thus, compared with aforementioned, non-categorical, phonetic features, the /o-ʌ/ pair can harm a phonological contrast, because there are many minimal-pair words in Korean containing these two vowels, such as /mol.ta/ “to herd (cattle)” and /mʌl.ta/ “far.” Therefore, the phonetic features of these two vowels appear to be more salient and easier to identify as a group-level property of the NK accent. Not pronouncing these two vowels, as in the SK dialect, does more than just harm the identification of words containing these vowels, but it also affects the social status of those who utter them. As most NK refugees are stigmatized because of their socio-political background, they try to adapt to SK to avoid potential discrimination. If the /o-ʌ/ pair contributes to the perceived NK accent as the most robust predictor, this is also socio-linguistically salient enough to elicit embarrassment and discrimination.

The present findings have pedagogical implications for both NK and SK speakers. When NK refugees arrive in South Korea, they attend an adaptation program to learn the SK language and culture for 12 weeks. Although the NK dialect is mostly intelligible to SK speakers, many NK refugees have difficulty learning the pronunciation of the second, SK dialect. For more effective learning within a limited time, NK refugee speakers need to know the differences between the NK and SK dialects and carefully investigate which differences have a greater impact on perceived NK accent. Simultaneously, the present findings can be utilized as a resource to educate SK speakers not to discriminate against NK refugee speakers owing to the pronunciation differences between these two dialects.

The present study has several potential limitations that would be important to address in future studies. First, the NK speakers who participated in this study varied in their demographic and linguistic backgrounds, and many participants were shown to have already adapted to the SK dialect within its many phonetic features because of the strong incentive to adapt to SK society. Without a control group representing NK speakers (unexposed to SK), it may be challenging to determine whether the NK refugees have fully adapted to SK, whether their speech patterns fall somewhere between NK and SK, or whether they align more closely with one variety over the other. The inclusion of NK speakers from a wide range of origins reflects the reality that the NK dialects encountered in SK society are often not specific dialects, but rather a mixture of dialectal features. Although the primary purpose of this study was not to provide a descriptive analysis of individual NK dialects but to explore the phonetic characteristics of perceived NK dialects, it is necessary to recruit more NK refugees with limited exposure to the SK dialect. Second, while the acoustic features for the NK accent were selected based on phonological descriptions or the results of acoustic measurements in prior work, the features not discussed in this study may also influence accent ratings. In particular, the target sentences for evaluating the intonation contour were relatively short, which may not reflect the variety of intonation patterns that occur in spontaneous speech. These issues should be addressed in future studies.

In conclusion, the present study examined the nature of perceived second-dialect features in the language production of NK refugees in Seoul, South Korea. Results demonstrated that among the phonetic features associated with vowel contrasts, stop and affricate contrasts, and intonation patterns, the spectral differences of the vowels /o/ and /ʌ/ played the most important role in the perception of NK dialect accent. The accent rating results were mostly consistent with predictions based on phonological and phonetic comparisons between the NK and SK dialects. The results of the present study can offer valuable insights into second dialect acquisition process by providing empirical data from NK refugees, un underexplored population in this field. Furthermore, the present findings have some important educational implications: They could help NK refugees learn the SK (second) dialect effectively and more importantly, to educate SK speakers not to discriminate against NK refugees based on dialect differences.