2.1 Morphology

It has been reported in the literature that n-insertion does or does not apply depending on the type of morpheme involved. Morphemes preceding and following the insertion site, called here M₁ and M₂, have been argued to be subject to different restrictions on the occurrence of n-insertion. I will first discuss previous proposals on the restriction of M₁ and then those of M₂.

2.2 Syllabicity of M₂-initial vocoid

It is widely assumed in the traditional literature on Korean phonology and morphology that n-insertion occurs not only before a high front vowel /i/ but also before a palatal glide /j/. However, some previous studies have argued either that the vowel /i/ is not a trigger of n-insertion, or that /i/ is less likely to trigger n-insertion than the glide /j/. Lee & Lee (2006: 422–4), Hong (2006: 397) and Ahn (2009: 263) deny the existence of synchronic pre-/i/ insertion in Korean, thus claiming that /j/ is the sole trigger of n-insertion. Lee (1996: 168), Bae (2003: 241), and Oh (2006: 125–9) acknowledge the existence of pre-/i/ insertion, but describe it as less frequent, or less naturally occurring, than pre-/j/ insertion. To summarize, /j/ is a stronger trigger of n-insertion than /i/, although it is controversial whether the difference in strength is categorical or gradient.

2.3 Sonorancy of C₁

Some previous studies have argued that the sonorancy of C₁ determines the likelihood that n-insertion will apply. According to Cho (1995: 610–11) and Cho & Iverson (1997: 702), Korean n-insertion applies obligatorily after a sonorant C₁ and optionally after an obstruent C₁.

A similar C₁ sonorancy asymmetry has been argued to hold for Sino-Korean words consisting of monosyllabic roots. In the description of Seoul Korean n-insertion presented by Oh (2006: 121–2) and followed by Ahn (2008: 384–5), Sino-Korean words consisting of monosyllabic roots undergo n-insertion only after a sonorant (e.g. /kʌm-jʌl/ [kʌmnjʌl] ‘censorship’), not after an obstruent (e.g. /pɛk-jʌl/ [pɛkjʌl] ‘white heat’). The same type of C₁ sonorancy asymmetry in Sino-Korean words can also be found in Lee’s (2006: 635–6, (24) vs. (27)) description of Kyungsang Korean n-insertion.

To summarize, the previous studies on the role of sonorancy of C₁ in the application of Korean n-insertion suggest that a sonorant C₁ is a stronger trigger of n-insertion than an obstruent C₁, although the exact strength and domain of the sonorancy asymmetry still need to be explored.

2.4 Exceptions and variation

As discussed above, traditional analyses of Korean n-insertion have attempted to explain the variation in n-insertion by restricting the domain of rule application in terms of the morphological category of M₁ and M₂, syllabicity of M₂-intial vocoids, and sonorancy of C₁, which may interact with additional factors such as dialect, etymology and/or length of the morphemes involved, as summarized in (4).

They mostly propose such factors to have categorical effects on variation while describing relevant patterns based mainly on the authors’ intuition as a native speaker of Korean.

However, some exceptions to each of those factors have already been pointed out in the previous studies based on the authors’ intuition, and even a wider range of exceptions were reported in experimental and survey studies on Korean n-insertion (Kim 2000; Choi 2002; Kim 2003). For instance, the free M₂ requirement (i.e. n-insertion applies to words with a free M₂) is neither a sufficient nor a necessary condition for the occurrence of n-insertion. Not all /i, j/-initial M₂ stems trigger n-insertion: e.g. /mas-is’-ta/ *[mannitt’a], [masitt’a] ‘delicious (taste-exist-SE)’. On the other hand, certain (/j/-initial) native Korean M₂ suffixes may trigger n-insertion: e.g. /camsi-man-jo/ [camsimannjo] ‘Wait a moment (moment-only-SE)’ (Bae 2003; Oh 2006). It seems that none of the conditioning factors proposed in the previous studies completely determine the occurrence or absence of n-insertion. In addition, as mentioned in a number of previous studies on Korean n-insertion (Kim-Renaud 1974/1991; Ko 1992; and many others), n-insertion is often optional. The probability of n-insertion may vary greatly across speakers and words, as can be seen in the results of previous experimental/survey studies on Korean n-insertion (Choi 2002; Kim 2003; and Jun 2015), and as is also evident from the data of this study presented in sections 3–4. The widespread exceptions and variation involved make Korean n-insertion look quite irregular. Nonetheless, it is still possible that the factors proposed in the previous literature may have gradient effect, contributing to the overall probability of n-insertion. In fact, such possibilities have been mentioned for some of the factors in the previous studies: for instance, a higher frequency or preference of n-insertion before /j/ than before /i/ (Lee 1996; Bae 2003; and Oh 2006) and a greater likelihood of n-insertion after a sonorant C₁ than after an obstruent C₁ (Han 1994). Unfortunately, the few claimed tendencies were mostly based on the authors’ intuition, rather than the results of wide-scale experimental or survey studies.

In the next section, I will provide a comprehensive and systematic investigation of n-insertion in existing Korean words to establish what factors affect n-insertion and whether they have categorical or gradient effects. For this purpose, I consider the following expanded set of factors:

The type of C₁, the length of component morphemes, and the height of V₂ are added to the list of factors, mainly because they have been shown to be active in the application of Seoul Korean n-insertion by some previous studies (Hwang 2008, Jun 2015). Note that the length of a word or morpheme has been identified as a factor affecting the rate of a phonological process such as Turkish final devoicing (Becker et al. 2011). It has, in fact, been shown in Jun (2015) that n-insertion in Seoul Korean is less likely with words with monosyllabic M₁ than those with longer M₁. As discussed in section 2.2, several previous studies on Korean n-insertion have argued for the effect of C₁ sonorancy. However, the results of Hwang’s (2008) experimental study and Jun’s (2015) survey on Seoul Korean speakers show that this C₁ sonorancy effect differs depending on the place of articulation of C₁ sonorants. Specifically, n-insertion is less likely after a velar nasal C₁ than after other sonorants. Thus, the present investigation will involve a comparison not only between words with obstruent vs. sonorant (except /ŋ/) C₁, but also between those with the velar nasal vs. other sonorant C₁. Jun also reports that the height of V₂ plays a significant role in determining the rate of Seoul Korean n-insertion, and, specifically, that insertion is more likely before a high vowel than before a non-high vowel. Finally, word frequency is added to the list in (5) as it has often been shown to affect the application rate of an optional process (for instance, English final t/d deletion as discussed by Coetzee and Pater 2011).

3.1 Data and experimental procedure

In this section, I explore n-insertion in existing Korean words by investigating the results of the surveys on native speakers of two dialects of Korean, Seoul and Kyungsang. For Seoul Korean data, I use the results of the survey conducted by Jun (2015). In that survey, twenty-two Seoul Korean speakers participated. For Kyungsang Korean data, I performed a survey on Kyungsang Korean speakers, using the same method and the same word set as adopted by Jun.

Twenty-three paid Kyungsang Korean speakers participated in the survey (mean age = 25.9 years, eleven females and twelve males). Most of the participants (n = 20) were raised in Daegu, and the rest (n = 3) in other parts of Northern Kyungsang province. Sixteen participants were recruited from the community at Seoul National University through public advertising, and they took the survey in a quiet room (for about 40–50 minutes). The rest of the participants (n = 7), who were recruited through personal referrals, completed and returned the survey via email.

304 multi-morphemic Korean words with /j/-initial M₂ were employed as test words. These formed an exhaustive set of words with /j/-initial M₂ that Jun classified as multi-morphemic in a pilot investigation of his dictionary database.⁴ No test words included /i/-initial M₂, mainly because it was clear from the results of Jun’s investigation of the data drawn from a dictionary and from previous surveys (Choi 2002, Kim 2003, Kook et al. 2005) that pre-/i/ insertion is attested, but less frequent in existing Korean words. Most of the test words were nouns (n = 286), and the exceptions included thirteen verbs and five adverbs.

A single survey form was used, and thus the tasks were administered in the same order for all participants. In the survey form, each test word along with its inserted and non-inserted forms were presented in standard Korean orthography.⁵ For each test word, the participants were instructed to choose their pronunciation from the following three (or two) options:

When C₁ was not /ŋ/ as in (6i–ii), two non-inserted forms (6b,c) were given in addition to an inserted one (6a). The resyllabified form (6b) is known as the standard surface form in Korean where an intervocalic consonant occupies an onset position. But, it has been argued in the literature (Lee 1992, Park 2001) that the aligned form (6c) is also possible when a morpheme boundary intervenes between a consonant and a following vocoid. When C₁ was /ŋ/ as in (6iii), only a single non-inserted option (6c) was given since there is no way to represent the resyllabified option (6b) in the standard Korean orthography, and it is generally assumed in Korean phonology that [ŋ] cannot be syllabified (at least exclusively) in onset position. When C₁ was underlyingly an obstruent as in (6ii), the option (6a) with insertion included nasalization of C₁ since obstruent nasalization is obligatory in Korean, as stated in section 2. The participants were allowed to choose more than one, each of which was counted as one data point in the analysis. Also, when their pronunciation was not given as an option, they were asked to write it in the blank space on the survey form. (See Jun (2015) for more details of the methods and the reason for conducting a self-evaluation survey using written forms.)

In order to construct a database for the analysis of n-insertion in existing Korean words, I first combined results of Jun’s survey on Seoul Korean speakers and the results of the present survey on Kyungsang speakers. The resulting data will be analyzed and discussed, using a statistical model and insertion rates (i.e. number of insertion responses divided by total number of responses).

I conducted data screening before the main analysis. Responses to certain sets of test words would cause difficulty in the analysis of the effects of the factors, presented above, on Korean n-insertion. First, I excluded the responses to a test word with a compound marker in C₁ position (/twi-s-jɛki/ ‘backbiting (back-COMPOUND MARKER-story)’) from the database. The phonological nature of the compound marker is controversial in the literature on Korean phonology and morphology: /s/, /t/, /ʔ/, empty skeletal slot and others.⁷ It is thus unclear which category the compound marker belongs to. It should probably not be classified as either obstruent or sonorant, although it is represented with the letter <s> in Korean orthography.

An additional problematic set of test words has the same M₂-initial suffix sequence /jʌ/, a contracted form of a causative suffix /i/ and a converbal suffix /ʌ/: e.g. /cuk-jʌ-cu-ta/ ‘be killing (die-CAUS.CVB-give-INF)’.⁸ This suffix sequence is the only native Korean M₂-intial suffix included in the test word set. There is almost no variation among responses to the words with it. Most Korean participants did not choose the insertion option for them. The insertion rates for the ten test words with /jʌ/ are either zero or close to it: 3 words (0%), 4 words (4%), 2 words (6%), 1 word (13%). Thus, it seems that n-insertion is blocked almost categorically before this suffix. In the analysis of the database, I excluded responses to the test words with /jʌ/ so that they cannot weaken the effects of the factors adopted for investigation. The resulting data consist of 13,484 responses to 293 test words (285 nouns, five adverbs and three verbs).

3.2 Raw data analysis

This section considers only overall patterns of the data by calculating the mean insertion rates for each of the factors adopted in the experiment. In the next section, I provide a statistical analysis of the same data.

3.2.1 Dialect

The mean insertion rate for the entire data is 51.4%, and the rate is, on average, higher for Kyungsang speakers than for Seoul speakers, as shown in Table 1 and Figure 1.

Table 1

Insertion rate (%) by dialect.

Dialect	rates
Seoul	45.2
Kyungsang	57.4

Figure 1

Insertion rate (%) by dialect.

The observed higher rate of insertion for Kyungsang speakers is consistent with previous studies (section 2.1.1), but it will be shown that the observed difference is not statistically significant.

3.2.2 Morphological category

To establish the effect of M₁ morphology, insertion rates were calculated for different morphological categories of M₁, as shown in Table 2.

Table 2

Insertion rate (%) by M₁ morphology.

M1 morphology	rates
root	33.1 (58)
stem	57.3 (215)
prefix	41.2 (20)

• (The number of corresponding words is shown in parentheses.)

Insertion rate was lowest for words with a bound root M₁, highest for those with a free stem M₁, and intermediate for those with a prefix M₁. This observed ranking by M₁ morphological category, root < prefix < stem, did not differ depending on the dialect of the participants, as shown in Table 3 and Figure 2.

Table 3

Insertion rate (%) by M₁ morphology and dialect.

M1 morphology	Seoul	Kyungsang
root	24.2	41.6
stem	51.8	62.6
prefix	34.0	48.0

Figure 2

Insertion rate (%) by M₁ morphology and dialect.

In addition, to establish the effect of M₂ morphology, insertion rates were calculated for different morphological categories of M₂, as shown in Table 4.

Table 4

Insertion rate (%) by M₂ morphology.

M2 morphology	rates
root	47.3 (62)
stem	51.3 (208)
suffix	64.7 (23)

• (The number of corresponding words is shown in parentheses.)

Insertion rate was lowest for words with a bound root M₂, highest for those with a suffix M₂, and intermediate for those with a free stem M₂. As can be seen in Table 5 and Figure 3, the observed ranking by M₂ morphological category, root < suffix < stem, did not differ across dialects.

Table 5

Insertion rate (%) by M₂ morphology and dialect.

M2 morphology	Seoul	Kyungsang
root	38.9	55.2
stem	45.6	56.6
suffix	58.5	70.6

In summary, n-insertion was more likely with a free stem or an affix than with a bound root, regardless of whether it precedes or follows the insertion site. In addition, the relative frequencies of n-insertion by morphological category did not differ by dialect.

Figure 3

Insertion rate (%) by M₂ morphology and dialect.

3.2.3 Etymology

To establish the effect of M₁ etymology, insertion rates were calculated for different etymological origins of M₁ morphemes, as shown in Table 6.

Table 6

Insertion rate (%) by M₁ etymology (loan = loanword).

M1 etymology	rates
sino	49.8 (250)
native	60.0 (39)
loan	68.7 (4)

• (The number of corresponding words is shown in parentheses.)

Insertion rate was, on average, lower when M₁ is Sino-Korean than native Korean. Although the rate was highest for words with a loanword, the test word set has only four words with a loanword M₁. As can be seen in Table 7 and Figure 4, the observed ranking by M₁ etymology, Sino-Korean < native Korean (< loanword), did not differ by dialect.

Table 7

Insertion rate (%) by M₁ etymology and dialect.

M1 etymology	Seoul	Kyungsang
sino	43.1	56.3
native	56.7	63.2
loan	64.0	73.1

Figure 4

Insertion rate (%) by M₁ etymology and dialect.

In addition, to establish the effect of M₂ etymology, insertion rates were calculated for different etymological origins of M₂ morphemes, as shown in Table 8.

Table 8

Insertion rate (%) by M₂ etymology.

M2 etymology	rates
sino	50.4 (267)
native	62.3 (26)

• (The number of corresponding words is shown in parentheses.)

Similarly to the results for M₁ etymology, insertion rate was lower when M₂ is Sino-Korean than native Korean. As can be seen in Table 9 and Figure 5, the observed relative rate difference between words with native and Sino-Korean M₂ did not differ by dialect.

Table 9

Insertion rate (%) by M₂ etymology and dialect.

M2 etymology	Seoul	Kyungsang
sino	43.7	56.8
native	60.3	64.2

Figure 5

Insertion rate (%) by M₂ etymology and dialect.

In summary, n-insertion was less likely with a Sino-Korean morpheme than with a native Korean (or loanword), regardless of whether it precedes or follows the insertion site. This tendency was true for both Seoul and Kyungsang speakers.

3.2.4 C₁ type

To establish how n-insertion varies depending on the type of C₁, insertion rates were calculated for different C₁ consonants, as shown in Table 10.

Table 10

Insertion rate (%) by C₁ consonants.

C1 type	C1	rates
obstruent	c	55.6 (1)
	th	64.4 (1)
	ph	51.1 (1)
	s	58.1 (3)
	p	51.1 (15)
	k	40.6 (48)
sonorant	l	65.6 (35)
	m	60.7 (18)
	n	55.5 (78)
	ŋ	46.2 (93)

• (The number of corresponding words is shown in parentheses.)

Excluding consonants with extremely low frequency (less than or equal to 3), insertion rates are plotted by C₁ consonants in Figure 6.

Figure 6

Insertion rate (%) by C₁ consonants.

Insertion rate was lower after an obstruent or velar nasal than after a sonorant other than /ŋ/, as shown in Table 11.

Table 11

Insertion rate (%) by C₁ type.

C1 type	rates
obs	44.2 (69)
son	58.9 (131)
ŋ	46.1 (93)

• (obs = obstruent, son = sonorant except /ŋ/; The number of corresponding words is shown in parentheses.)

The observed lower insertion rates with an obstruent or /ŋ/ C₁ are true for both Seoul and Kyungsang speakers, as can be seen in Table 12 and Figure 7.

Table 12

Insertion rate (%) by C₁ type and dialect.

C1 type	Seoul	Kyungsang
obs	42.8	45.5
son	51.1	66.3
ŋ	38.6	53.5

Figure 7

Insertion rate (%) by C₁ type and dialect.

The relative rate difference between words with an obstruent and velar nasal C₁ was switched between the participants of the two dialects: obstruent > /ŋ/ for Seoul, but obstruent < /ŋ/ for Kyungsang.

In summary, n-insertion was less likely after an obstruent or velar nasal than after other sonorant consonants, regardless of the dialect of the participants.

3.2.5 Length

To establish how n-insertion varies depending on the length of M₁, insertion rates were calculated for different numbers of component syllables of M₁, as shown in Table 13.

Table 13

Insertion rate (%) by the number of syllables of M₁.

number of M1 syllables	rates
1	38.9 (130)
2	61.1 (154)
3	71.7 (7)
4	31.9 (1)
5	73.3 (1)

• (The number of corresponding words is shown in parentheses.)

Insertion rate was higher when M₁ is disyllabic than monosyllabic. The insertion rate is even higher when M₁ is trisyllabic, suggesting that as the M₁ length increases, the more likely n-insertion is. But, since words with trisyllabic syllables or longer are relatively few in the test set, I take the above rate distribution as indicating the difference between words with mono and polysyllabic M₁, collapsing the results for words with polysyllabic M₁, as shown in Table 14.

Table 14

Insertion rate by (%) M₁ length.

M1 length	rates
monosyllabic	38.9 (130)
polysyllabic	61.5 (163)

• (The number of corresponding words is shown in parentheses.)

The observed higher rate of insertion with polysyllabic M₁ is true for both Seoul and Kyungsang participants, as shown in Table 15 and Figure 8.

Table 15

Insertion rate (%) by M₁ length and dialect.

	Seoul	Kyungsang
monosyllabic	31.0	46.3
polysyllabic	56.4	66.4

Figure 8

Insertion rate (%) by M₁ length and dialect (poly = polysyllabic).

In addition, to establish how n-insertion varies depending on the length of M₂, insertion rates were calculated for different numbers of component syllables of M₂, as shown in Table 16.

Table 16

Insertion rate (%) by the number of syllables of M₂.

number of M2 syllables	rates
1	51.2 (148)
2	51.3 (131)
3	58.2 (12)
4	40.8 (2)

• (The number of corresponding words is shown in parentheses.)

Insertion rate does not seem to vary systematically with the length of M₂. There is almost no difference in average insertion rate between words with mono and disyllabic M₂. Words with trisyllabic M₂ show somewhat higher rates, but words with trisyllabic M₂ or longer are relatively few in the test set. Thus, as in the analysis of M₁ length effects, I collapsed the results of all words with polysyllabic M₂ into a single category. Its average insertion rate is 51.8%, which is not substantially different from the rate for words with monosyllabic M₂, i.e. 51.2%, as shown in Table 17.

Table 17

Insertion rate (%) by M₂ length.

M2 length	rates
monosyllabic	51.2 (148)
polysyllabic	51.8 (145)

• (The number of corresponding words is shown in parentheses.)

The rate (non-)difference between words with mono and polysyllabic M₂ did not vary much by dialect, as shown in Table 18 and Figure 9.

Table 18

Insertion rate (%) by M₂ length and dialect.

	Seoul	Kyungsang
polysyllabic	45.8	57.4
monosyllabic	44.5	57.5

Figure 9

Insertion rate (%) by M₂ length and dialect.

In summary, insertion rates differed according to the length of M₁, not M₂, regardless of the dialect of the participants. n-insertion was more likely with a polysyllabic M₁ than with a monosyllabic M₁.

3.2.6 V₂ height

To establish the effect of the quality of a vowel following /j/, called V₂, insertion rates were calculated for different V₂ vowels, as shown in Table 19 and Figure 10.

Table 19

Insertion rate (%) by V₂ vowels.

V2	rates
a	45.9 (73)
ʌ	51.2 (139)
e	52.6 (4)
o	52.4 (43)
u	62.7 (34)

• (The number of corresponding words is shown in parentheses.)

Figure 10

Insertion rate (%) by V₂ vowels.

Insertion rate was higher when V₂ is /u/, namely, a high vowel (62.7%), than when V₂ is non-high (49.9%), as shown in Table 20.⁹

Table 20

Insertion rate (%) by V₂ height.

V2 height	rates
non-high	49.9 (259)
high	62.7 (34)

The observed higher rate of n-insertion with a high V₂ is true for both Seoul and Kyungsang participants, as can be seen in Table 21 and Figure 11.

Table 21

Insertion rate (%) by V₂ height and dialect.

V2 height	Seoul	Kyungsang
non-high	43.6	56.1
high	57.6	67.7

Figure 11

Insertion rate (%) by V₂ height and dialect.

In summary, n-insertion was more likely before a high vowel than before non-high vowels. This observed tendency was true for both Seoul and Kyungsang participants.

3.2.7 Frequency

To establish how n-insertion varies depending on the frequency of words, insertion rates were calculated for different (log-transformed) frequencies, and plotted in Figure 12.

Figure 12

Insertion rate (%) by (log-transformed) frequency (n = 293).

Here we use word frequencies in the Sejong corpus, reported in Kang and Kim (2004). It seems that frequencies played no role in determining the rate of n-insertion, as suggested by an almost flat regression line in Figure 12, and by a statistically insignificant low correlation between insertion rates and (log-transformed) frequencies (r(291) = –0.040, p = 0.487).

The observed lack of frequency effect did not differ depending on the dialect of the participants, as can be seen in (7).

1. (7)

1. Correlations between insertion rates and frequency
2. 

3.3 Mixed effects analysis

In the previous section, we have considered only mean insertion rates, abstracting away from differences of individual participants and words. Here, we provide a more stringent test by taking into consideration individual participant and word differences. A mixed effects logistic regression model was fitted with the glmer function from the lmerTest package (Kuznetsova et al. 2017) in R (R Core Team 2020). Dependent variable is binary, i.e. n-inserted or not. Each subject and each test word were included as random intercepts.¹⁰

In the model on the data of existing words, the following independent variables were adopted.¹¹ (sel = Seoul, ks = Kyungsang)

• dialect (sel, ks)

• M₁ morphology (root, stem, prefix)

• M₂ morphology (root, stem, suffix)

• M₁ origin (sino, non-sino (native and loan))

• M₂ origin (sino, native)

• M₁ length (mono, poly)

• M₂ length (mono, poly)

• C₁ type (obs, son, ŋ)

• V₂ height (high, non-high)

• log-transformed token frequency (frequency)

The interactions of dialect with each of all the remaining variables were included to address the question of whether the effect of each variable varies across dialects. The following interactions were additionally included in the model based on the results of a CART (Classification and Regression Tree) analysis of each of Seoul and Kyungsang Korean data using the rpart package (Therneau & Atkinson 2019).¹²

• 2-way interaction between M₁ origin and M₁ length

• 3-way interaction between dialect, M₁ length and frequency

• 3-way interaction between dialect, M₁ length and C₁ type

• 3-way interaction between dialect, M₁ origin and C₁ type

Categorical factors with three levels, M₁,₂ morphology and C₁ type, were forward-difference coded in order to compare not only between the first and second levels (e.g. root vs. stem), but also between the second and third levels (e.g. stem vs. affix). All the remaining categorical factors were sum-coded so that coefficient estimates would represent the main effect.

The random effects of the mixed effects model show large variation depending on the participant (variance = 1.178) and test word (variance = 0.886), meaning that different participants and test words show greater and lesser average rates of insertion, as can be seen in Figures 13 and 14, respectively.

Figure 13

The numbers of participants for different insertion rates (bin width = 10).

Figure 14

The numbers of test words for different insertion rates (bin width = 10).

Even once these random factors are taken into account, as can be seen in (8), many fixed factors and their interactions still have a sizable effect on the insertion rate, which holds independently of the specific participant and test word.

(8)	Results of a mixed effects logistic regression model13

The next section discusses the results of the present survey focusing on the significant effects in the mixed effects model, just presented.

3.4 Significant effects

The significant main effects in the mixed effects model, shown in (8), are summarized in (9).

All of these main effects can also be seen in the corresponding tables and plots presented in section 3.2. Many of them are in part or probabilistically consistent with previous studies on Korean n-insertion, discussed in section 2 and summarized in (4). Let us consider each of the significant main effects.

First, the M₁ morphology effect (9a) suggests that a bound root M₁ is less likely triggers of n-insertion than a free stem M₁ in both dialects. This and other related findings are only in part consistent with previous studies on Korean n-insertion. As discussed in section 2.1, Han (1994) argues that n-insertion may occur after a free stem, regardless of the dialect, but dialectal variation occurs with words with a bound root M₁. It is argued that n-insertion is blocked after a bound root in Seoul, not Kyungsang, Korean. The results of the present study agree with Han’s argument in that n-insertion is more frequent after a free stem in Seoul Korean. However, the present study differs from the previous studies in that n-insertion in Seoul Korean was not completely blocked after a bound root M₁, as can be seen in Table 3 and Figure 2. Some test words with a bound root M₁, for which Seoul Korean participants applied n-insertion frequently, are shown in (10).

Consequently, the observed dialectal difference with respect to M₁ morphology is consistent with a probabilistic version of Han’s argument on the difference between Seoul and Kyungsang Korean n-insertion.

Second, the M₂ morphology effect (9b) is similar to the M₁ morphology effect, just discussed, in that roots are less likely to trigger n-insertion than stems and affixes. Note that n-insertion occurred when M₂ is a bound root (and affix), as can be seen in Tables 4, 5 and Figure 3. This observation is in conflict with the free M₂ requirement proposed in many previous studies on Seoul Korean n-insertion, mentioned in section 2.1.2. Since all M₂ roots and suffixes in the present data are Sino-Korean, this study provides no counter-examples to the native Korean specific version of the free M₂ requirement. But, recall, in section 2.4, that cases of n-insertion before certain native Korean suffixes have already been reported in some previous studies. Consequently, the free M₂ requirement cannot be an absolute condition for n-insertion in Korean words, whether native or Sino-Korean. But, it seems true that n-insertion is blocked categorically before certain native Korean bound morphemes, as suggested by the results of the present survey involving the causative-converb suffix sequence /jʌ/, discussed in section 3.1.

Third, insertion rates differed depending on the type of C₁. Two observed relevant effects, obstruency (9c) and velar nasal (9d), suggest that sonorant consonants other than /ŋ/ are frequent triggers of n-insertion. This is only in part consistent with the previous studies on Seoul Korean n-insertion (Cho 1995, Cho & Iverson 1997) arguing that n-insertion applies obligatorily after a sonorant consonant, and optionally after an obstruent. One difference of the present study from the previous studies is that n-insertion did not always apply in words with a sonorant C₁. As illustrated in (11), Seoul Korean participants rarely applied n-insertion in some words with a sonorant C₁.

Thus, the observed obstruency effect is consistent with a probabilistic version of the previous argument on the difference between sonorant and obstruent C₁ consonants. The velar nasal effect (i.e. /ŋ/ is not a likely trigger of n-insertion unlike other sonorant consonants) forms the second difference of the present study from the above-mentioned previous studies. The observed velar nasal effect is consistent with the results of Hwang’s (2008) experimental study on Seoul Korean n-insertion.

Fourth, the length effect suggests that a polysyllabic M₁ is more likely triggers of n-insertion than a monosyllabic M₁, regardless of the dialect of the participants. See below for a discussion of significant interaction effects of the length factor with some other factors.

Finally, insertion rates differed depending on the height of V₂ vowels following the M₂-initial /j/. The height effect suggests that high V₂ vowels are likely triggers of n-insertion than non-high vowels.

Some of the significant main effects, just discussed, interact with other factors in the present data. Significant interaction effects in the mixed effects model, shown in (8), are summarized in (12).

Let us discuss these significant interaction effects.

Four interaction effects in (12a–d) indicate how C₁ type effects, obstruency and velar nasal, varied according to dialect, M₁ length, and/or M₁ origin. The larger obstruency effect for Kyungsang speakers (12a) can be seen in Table 12 and Figure 7. This indicates that obstruent consonants are even weaker triggers of n-insertion for Kyungsang speakers than for Seoul speakers. But, the interaction effect in (12b) suggests that this is mainly true for words with monosyllabic M₁ since the obstruency effect for Kyungsang speakers is larger with monosyllabic M₁ than with polysyllabic M₁, as can be seen in Table 22 and Figure 15.

Figure 15

Insertion rate (%) in Kyungsang Korean data by C₁ type and M₁ length.

The observed stronger obstruency effect with monosyllabic M₁ in the present Kyungsang data is probabilistically consistent with Lee’s (2006) description of Kyungsang Korean n-insertion, discussed in section 2.3, which says that Kyungsang Korean n-insertion occurs only after sonorants, not obstruents, in Sino-Korean words consisting of monosyllabic root morphemes.¹⁴ As stated in (12c), the velar nasal effect also interacts with dialect and M₁ length, but in the opposite direction. As can also be seen in Table 22 and Figure 15, the velar nasal effect is larger with polysyllabic M₁ morphemes in Kyungsang Korean data. As stated in (12d), the velar nasal effect also interacts with M₁ origin. The velar nasal effect is smaller with Sino-Korean M₁ in Kyungsang Korean data, as can be seen gTable 23 and Figure 16.

Figure 16

Insertion rate (%) in Kyungsang Korean data by C₁ type and M₁ origin.

In addition, the interaction between M₁ length and M₁ origin (12e) indicates that the length effect was larger with a Sino-Korean M₁ than with a native Korean M₁, as shown in Table 24 and Figure 17.

Figure 17

Insertion rate (%) by M₁ origin and M₁ length (sino = Sino-Korean).

Note in fact that the M₁ length effect can be seen only among words with Sino-Korean M₁ which formed the majority of the test words.

Finally, although frequency plays no role in predicting rates of Korean n-insertion in the entire data set, as shown in section 3.2.7, it is a significant predictor in a subset of the Seoul Korean data consisting of words with a polysyllabic M₁ (12f). For Seoul Korean participants, words with a polysyllabic M₁ tend to undergo n-insertion more frequently as their token frequencies increase, as indicated by the correlation presented in (13) and a regression line in Figure 18.

Figure 18

Insertion rate (%) by (log-transformed) frequency (dialect = Seoul, M₁ length = polysyllabic, n = 163).

3.5 Summary

All the significant effects, main or interaction, discussed above, are summarized in (14)

The probability of n-insertion in existing Korean words is significantly affected by various factors, as summarized above. Most of the factors do not completely determine the occurrence or absence of n-insertion, but they have gradient effect, contributing to the overall probability. The next section deals with whether, and which of, the gradient effects found in this section Korean speakers are aware of. We will focus on the effects of dialect, C₁ type, M₁ length, and V₂ height, which can readily be tested with novel words. The rest of the factors tested in the survey on existing words were excluded from the novel word survey mainly due to the difficulty in creating appropriate test items. For instance, it was unclear how to construct words with novel bound roots and novel Sino-Korean, as opposed to native Korean, words.

4.1 Data and experimental procedure

This section explores n-insertion in novel Korean words by investigating the results of the surveys on native speakers of two dialects of Korean, Seoul and Kyungsang. As in section 3, for novel word data of Seoul Korean speakers, I use the results of a novel word survey conducted by Jun (2015). The results are from responses of thirty-seven Seoul Korean speakers. For Kyungsang Korean data, I performed a survey on Kyungsang Korean speakers, using the same method and the same word set as adopted by Jun.

In total, thirty-two paid Northern Kyungsang Korean speakers participated in the test (mean age = 25.1 years, 17 females and 15 males). None of them participated in the survey with existing words. Most of the participants (n = 24) were raised in Daegu, and the rest (n = 8) in other parts of Northern Kyungsang province. All participants were recruited from the community at Seoul National University through public advertising and personal referrals. Twenty-eight participants took the survey in a quiet room (for about 25–35 minutes). The rest of the participants (n = 4) completed and returned the survey via email.

All test words consist of loanword M₁ and wug stem M₂. M₁, which is either mono or disyllabic, ends with one of seven consonants, /m, n, ŋ, l, p, s, k/. M₂ begins with one of /i, ju, ja/. The total number of test items is 84 (2 syllable counts × 7 codas × 3 vocoid types × 2 repeating blocks). The same number of control items (vowel-final M₁ or /a, e/-initial M₂) were adopted. The items were pseudorandomized in order, such that test items never followed each other and were always separated by a control item. Two sets of items were prepared: one set was the reversed version of the other.

In the survey form, two parts of a word, M₁ and M₂, along with its inserted and non-inserted forms, were presented in standard Korean orthography. The experimenter told the participants that the combination of the two parts is a made-up compound noun for a new chemical product. The participants were instructed to choose their pronunciation of each of the given compounds from the following three (or two) options.

Like in the survey of existing words, when C₁ is /ŋ/ as in (15iii), only two options (15a,c) were given. When C₁ was underlyingly an obstruent as in (15ii), the option (15a) with insertion included nasalization of C₁ due to obstruent nasalization. The participants were allowed to choose more than one, each of which was counted as one data point in the analysis. Also, when their pronunciation was not given as an option, they were asked to write it in the blank space on the test form.

In order to construct the database for analysis of n-insertion in novel Korean words, I first combined results of Jun’s (2015) survey on Seoul Korean speakers and the results of the present survey on Kyungsang speakers. Two Seoul Korean speakers inserted more frequently in control tokens than target tokens, which I think is beyond the permissible range of errors. Their responses were considered not reliable, and thus excluded from analysis. After further excluding responses to fillers with vowel-final M₁, the resulting data consist of 9,814 responses.

An initial investigation of the novel word data shows clear syllabicity effect of M₂-initial vocoids (i.e. n-insertion is less likely before /i/ than /j/), as can be seen in Table 25.

Insertion rate is obviously higher before a glide /j/ than before vowels. But, /i/ is not higher in insertion rate than control vowels /a, e/, suggesting that insertion before /i/ is no more productive than insertion before other vowels.

Given that only pre-/j/ insertion is productive, the remainder of the analysis will focus on the data for test words with /j/-initial M₂, which consist of 3,957 responses. This will facilitate a direct comparison between the patterns of novel and existing Korean words. As in section 3, the novel word data will be analyzed, first using mean insertion rates and then using a mixed effects logistic regression model.

4.2 Raw data analysis

This section discusses only overall patterns of the data by calculating the mean insertion rates for each of the factors adopted in the experiment. The next section provides a statistical analysis of the same data.

4.2.1 Dialect

The mean rate of insertion for the entire data set is 31.4%, and the rate is higher for Kyungsang speakers than for Seoul speakers, as shown in Table 26 and Figure 19.

Table 26

Insertion rate (%) by dialect.

dialect	rates
Seoul	29.2
Kyungsang	33.8

Figure 19

Insertion rate (%) by dialect.

It will be shown that the observed difference is not statistically significant, as in the results of the existing word survey.

4.2.2 C₁ type

Insertion rates were calculated for different C₁ consonants, as shown in Table 27 and Figure 20.

Table 27

Insertion rate (%) by C₁ consonants.

C1 type	C1	rates
obstruent	p	24.4
	s	26.3
	k	29.2
sonorant	m	29.8
	n	38.4
	l	49.6
	ŋ	21.5

Figure 20

Insertion rate (%) by C₁ consonants.

Insertion rates were higher with all three sonorant consonants, /m, n, l/, than with obstruents and /ŋ/, although the difference between /m/ and /k/ is very small. To establish the effects of C₁ type, i.e. obstruency and velar nasal effects, which were significant in existing words, insertion rates were calculated for obstruents, /ŋ/ and other sonorant consonants, as shown in Table 28.

Table 28

Insertion rate (%) by C₁ type.

C1 type	rates
obs	26.6
son	39.4
ŋ	21.5

Note that n-insertion in novel words is less likely after obstruents and /ŋ/ than after other sonorant consonants, just like in existing words. The observed lower insertion rates with an obstruent or /ŋ/ C₁ are true for both Seoul and Kyungsang speakers, as can be seen in Table 29 and Figure 21.

Table 29

Insertion rate (%) by C₁ type and dialect.

C1 type	Seoul	Kyungsang
obs	23.7	29.7
son	37.6	41.3
ŋ	20.1	23.1

Figure 21

Insertion rate (%) by C₁ type and dialect.

The ranking by C₁ type, son > obs > /ŋ/, in novel words did not differ by dialect, which is not consistent with the corresponding results of the existing word survey where insertion rate in Kyungsang Korean data was higher with /ŋ/ C₁ than with an obstruent C₁, unlike in Seoul Korean data.

In summary, n-insertion was less likely after an obstruent or velar nasal than after other sonorant consonants, regardless of the dialect of the participants. These tendencies in novel words are consistent with the tendencies, called obstruency and velar nasal effects, found in existing words.

4.2.3 Length

To establish the effect of M₁ length, insertion rates were calculated for different lengths of M₁, as shown in Table 30.

Table 30

Insertion rate (%) by M₁ length.

M1 length	rates
monosyllabic	33.3
polysyllabic	29.5

Insertion rate in novel words is higher with a monosyllabic M₁, which is not consistent with the corresponding results of the existing word survey. The observed higher rate of insertion with monosyllabic M₁ is true for both Seoul and Kyungsang participants, as shown in Table 31 and Figure 22.

Table 31

Insertion rate (%) by M₁ length and dialect.

	Seoul	Kyungsang
polysyllabic	26.5	32.8
monosyllabic	31.9	34.8

Figure 22

Insertion rate (%) by M₁ length and dialect.

In summary, n-insertion was more likely with monosyllabic M₁ than with polysyllabic M₁, regardless of the dialect of the participants. This is the opposite of the tendency observed in existing words, that is, higher rates with a polysyllabic M₁. Consequently, the results of the existing and novel word surveys are not consistent with each other with respect to the effect of M₁ length. (See section 5.2 for a further discussion.)

4.2.4 V₂ height

To establish the effect of the height of a vowel following /j/, called V₂, insertion rates were calculated for high and non-high V₂ vowels, as shown in Table 32.

Table 32

Insertion rate (%) by V₂ height.

V2 height	rates
non-high	27.3
high	35.3

Insertion rate in novel words was higher before a high V₂ than before a non-high V₂, which is consistent with the corresponding results of the existing word survey. This observed higher rate of n-insertion with a high V₂ is true for both Seoul and Kyungsang participants, as can be seen in Table 33 and Figure 23.

Table 33

Insertion rate (%) by V₂ height and dialect.

V2 height	Seoul	Kyungsang
non-high	25.2	30.0
high	33.2	37.6

Figure 23

Insertion rate (%) by V₂ height and dialect.

In summary, n-insertion was more likely with a high V₂ than with a non-high V₂, regardless of the dialect of the participants. This tendency in novel words is consistent with the tendency, called height effect, found in existing words.

4.3 Mixed effects analysis

As in the analysis of existing Korean words, a mixed effects logistic regression model was fitted with the glmer function from the lmerTest package (Kuznetsova et al. 2017) in R (R Core Team 2020). Dependent variable is binary, i.e. n-inserted or not. Each subject and each test word were included as random intercepts.

In the model on the data of novel words, the following independent variables were adopted.

• dialect (sel, ks)

• M₁ length (mono, poly)

• C₁ type (obs, ŋ, son)

• V₂ height (high, non-high)

The interactions of dialect with all the remaining factors were included to address the question of whether the effect of each variable varies across dialects. As in the analysis of existing words, I have conducted a CART (Classification and Regression Tree) analysis of each of Seoul and Kyungsang Korean data using the rpart package (Therneau & Atkinson 2019), in order to determine which interactions are active in the novel word data. Although no interactions turned out to be active in the novel word data, I have added a following interaction which was significant in existing words and can be tested in novel words: a 3-way interaction between dialect, M₁ length and C₁ type. As in the analysis of existing word data, C₁ type with three levels was forward-difference coded, and all the remaining categorical factors were sum-coded.

As in the analysis of existing word data, the random effects of the mixed effects model show variation depending on the participant (variance = 2.814) and test word (variance = 0.124), meaning that different participants and test words show greater and lesser average rates of insertion. Even after these random factors are taken into account, as can be seen in (16), some fixed factors still have a sizable effect on the insertion rate, which holds independently of the specific participant and test word.

(16)	Results of a mixed effects logistic regression model (novel words)15

The next section discusses the results of the novel word survey focusing on the significant effects in the mixed effects model, just presented.

4.4 Significant effects

Unlike in existing word data in which several main and interaction effects were significant, only the main effects involving C₁ type and V₂ height turned out to be significant (a = 0.05) in novel word data, as summarized in (17)

All of these main effects can also be seen in the corresponding tables and plots presented in section 4.2. Let us discuss these significant effects.

Insertion rates differed depending on the type of C₁. Two observed relevant effects, obstruency (17a) and velar nasal (17b), suggest that sonorant consonants other than /ŋ/ are frequent triggers of n-insertion in novel Korean words. Recall in section 3 that the two observed effects involving C₁ type, obstruency and velar nasal, were also found significant in the existing word data. This suggests that both obstruency and velar nasal effects were extended to novel words.

In addition, the height effect (17c) suggests that a high V₂ vowel is a more likely trigger of n-insertion in novel words than non-high V₂ vowels. Recall in section 3 that this V₂ height effect was also significant among existing words, indicating that the V₂ height effect was extended to novel words.

To summarize the results of the survey with novel Korean words, three main effects, obstruency, velar nasal and V₂ height, were confirmed. None of the remaining effects, main or interaction, were significant. As will be discussed in section 5.2, these results suggest that Korean speakers can learn prominent patterns among existing words through phonological generalizations.

5.1 Motivation, constraint and P-map effects

To illustrate how to analyze the occurrence of n-insertion, consider inserted and non-inserted forms shown in (18).

If /n/ is not inserted, C₁ consonants at the end of M₁ would be either resyllabified into the onset of M₂-initial syllable as in (18a) or be aligned with the end of the M₁-final syllable as in (18b). The non-inserted forms with resyllabification in (18a) involves a misalignment between morpheme and syllable boundaries. Many previous analyses of Korean n-insertion have argued, or assumed, that n-insertion is motivated by the requirement to align morpheme-syllable boundaries (Jun 2015 and references therein). In the non-inserted forms with alignment in (18b), vocoids /i, j/ initiate a syllable, leaving the preceding C₁ consonants at the end of M₁-final syllable. This syllable structure is marked in Korean where an intervocalic consonant (with the possible exception of /ŋ/) is syllabified as an onset. In terms of Optimality Theory (Prince & Smolensky 1993/2004), the forms with resyllabification and alignment violate the alignment constraint (“The right edge of a morpheme coincides with the right edge of a syllable.”) and syllable structure constraints, respectively. The relevant syllable structure constraints here include ONSET (“Syllables have an onset.”) and VOCOID-NUCLEUS (“Every [–consonantal] segment must be in the nucleus.”). The former penalizes aligned forms with a vowel-initial syllable (e.g. [som.i.pul]) whereas the latter penalizes those with a glide-initial syllable (e.g. [com.jak]). In contrast, the forms with n-insertion in (18c) satisfy both the alignment and syllable structure constraints at the cost of violating the constraint militating against insertion of a segment, namely DEP. The epenthetic /n/ initiates M₂-initial syllables, not only aligning between morpheme and syllable boundaries, but also avoiding syllables with no (or a bad, i.e. [-consonantal]) onset. To summarize, a consonant needs to be inserted at the beginning of M₂ to obey the alignment and syllable well-formedness constraints.

Let us now consider the questions of why /n/, not any other consonant, is inserted, and why insertion takes place only before high front vocoids. Jun (2015) answers these questions by arguing that /n/ in Korean is perceptually weak in the context of n-insertion, i.e. before high front vocoids /i, j/. Specifically, Jun’s analysis of Korean n-insertion is couched within the framework of Steriade’s (2001, 2009) P-map theory, which proposes that it is segments with low perceptibility that are typically inserted or deleted, due to the fixed ranking of faithfulness constraints reflecting the relevant perceptibility scale. In Korean, if /n/ occurs before high front vocoids /i, j/, it undergoes allophonic palatalization, failing to induce coarticulatory changes on the following vocoids. Thus, the input–output pairs i–ni (or, more precisely, i–ɲi) and j–nj (or j–ɲj) are perceptually more similar pairs, compared to other pairs such as i-mi and a-na. This suggests not only that insertion of /n/ before high front vocoids is perceptually less salient than insertion of other consonants in the same environment, but also that insertion of /n/ is less salient before high front vocoids than before other vocoids. Consequently, /n/ is inserted before high front vocoids because it is the segment most confusable with zero there.

A similar P-map-based account can be given for some of the observed effects, syllabicity and V₂ height. In Korean, unlike /ni/, the sequence /nj/ is phonetically realized almost as a single segment [ɲ], as stated in footnote 2. Thus the input–output pair j–nj is perceptually almost identical to j–ɲ, which must be more similar than i–ɲi, since the difference is less than a single segment in the former, but the entire segment [ɲ] in the latter. Also, the degree of perceptual modification involved in pre-/j/ n-insertion differs depending on the height of the vowel following /j/. /j/ normally coarticulates with a following vowel. When /j/ is followed by a high vowel, its low-frequency resonance, which it shares with nasals, can be fully maintained, making it perceptually more similar in nasality to its corresponding output with n-insertion, i.e. [ɲ]. But when it is followed by a non-high vowel, /j/’s low-frequency resonance is not maintained for as long, making it less nasal-like, so that the relevant pair is less similar. The height effect can be attributed to this difference in perceptual similarity between the input–output pairs with high and non-high vowels. To summarize, Korean n-insertion is more likely before a glide /j/ (cf. /i/) and a high V₂ (cf. non-high V₂) since /n/ is more confusable with zero in those environments.

Let us now consider the rest of the observed tendencies. Hwang (2008) and Jun (2015) have attributed the obstruency effect to automatic obstruent nasalization in Korean. If n-insertion applied to words with obstruent C₁, C₁ would become a nasal, violating ID(sonorant) (“Do not change the value of [sonorant].”). Since inserted forms of words with M₁-final sonorants would not violate ID(sonorant), other things being equal, n-insertion would be less likely after an obstruent than after a sonorant.

Jun (2015) has explained the velar nasal effect by arguing that an intervocalic /ŋ/ in Korean can be ambisyllabic. Given that non-inserted forms with an ambisyllabic C₁ may satisfy the alignment constraint, the demand for n-insertion would be less strong for words with /ŋ/ C₁, which is consistent with the velar nasal effect.¹⁶

The M_1,2 morphology effects (“n-insertion is more likely with stems or affixes than with roots.”) and lexical effects found in existing Korean words may be explained by indexing some of the constraints, discussed above, to morphological categories and lexical items (Archangeli & Pulleyblank 2002, Pater 2007). For instance, the prefix-specific version of alignment constraint would encourage n-insertion to occur after a prefix.

Thus far, it has been shown that not only the occurrence of n-insertion but also most of the observed effects (except the length effect) can be explained based on universal phonological constraints and assumptions specific to Korean phonology. Finally, note that a complete formal analysis of the current n-insertion data with much variation need to and can be couched within a probabilistic constraint grammar, as suggested by Jun’s (2015) analysis of Seoul Korean n-insertion based on the maximum entropy harmonic grammar (Hayes & Wilson 2008).

5.2 Does learning match data?

This section discusses whether the tendencies observed in existing Korean words were mirrored in novel words, in order to establish whether learning matches data. Specifically, it compares the patterns of existing words, presented in section 3, with those of novel words with /j/-initial M₂, presented in section 4.

The overall insertion rate of novel words, 31.4%, is much lower than that of the existing words, 51.4%. It is then expected that the size of an effect in existing words would be reduced in novel words, and only strong tendencies in the lexicon can be extended to novel words with statistical significance. In fact, three main effects in novel word data were significant (a = 0.05), as summarized in (17), and no other main and interaction effects were significant. Recall in section 3 that all the three significant effects in novel word data were also significant in existing word data. It suggests that Korean speakers are aware of each of the corresponding tendencies in the lexicon, and they used this knowledge in the novel word survey.

What about the rest of the tendencies tested in the novel word survey? All of them, which turned out to be insignificant in novel words, involve M₁ length and dialect. In the remainder of this subsection, I will consider the M₁ length effect, postponing the discussion of dialect effects to the next section.

As shown in section 4.2.3, insertion rate in novel words was higher with monosyllabic M₁. The relevant difference was not significant in the mixed effect model shown in section 4.3 (M₁ length (poly): b = –0.151, p = 0.098). This statistically insignificant tendency in novel words is the opposite of the tendency in existing words. Thus, this cannot be a case where the size of a lexical tendency is simply reduced in novel words. This suggests that Korean speakers failed to learn the tendency involving the M₁ length of existing words. This mismatch has been reported by Jun (2015), from which the Seoul Korean data of the present study are drawn. The insignificant interaction between M₁ length and dialect shown in (16), along with the insertion rates calculated in novel words for different lengths of M₁, shown in Table 31 and Figure 22, suggest that the failure of extending the length effect to novel words was not confined to Seoul Korean speakers. Jun attributes the observed mismatch between data and learning to the lack of a phonetic/phonological motivation for the tendency related to the length of M₁. Recall in the previous section that not only the occurrence of n-insertion but also most of the observed effects, except the length effect, can be explained in a phonetically and/or phonologically plausible way. It has been argued in the literature (Hayes et al. 2009, Becker et al. 2011, Hayes & White 2013) that lexical patterns lacking phonetic/phonological naturalness either cannot be learned or can be learned with much difficulty. Thus, the lack of phonetic/phonological naturalness seems to be a potentially plausible account of why the length effect in the lexicon failed to extend to novel words. To explain the failure of extending the length effect to novel words, one might consider a possibility that Korean speakers applied n-insertion in the novel word survey using their knowledge of patterns in existing native, not Sino-Korean, words. Recall, as shown in Table 24 and Figure 17 that the M₁ length effect was effective mainly in existing words with Sino-Korean, not native, M₁. However, it is unclear not only why Korean speakers ignored distributional patterns in Sino-Korean words which form the majority of the Korean lexicon, but how they successfully distinguished native Korean morphemes from Sino-Korean ones.

To summarize, three tendencies, i.e. obstruency, velar nasal and V₂ height effects, observed from the novel words mirror those from existing words, indicating a match between learning and data. This suggests that speakers can generalize gradient statistical patterns in the lexicon, as has been confirmed in many previous studies (Jun & Albright 2017 and references therein). An obvious mismatch involves the length effect, which may possibly lack phonetic/phonological naturalness.

5.3 Dialectal variation and remaining problems

One of the aims of the present study is to explore dialectal variation in Korean n-insertion. In this section, I will first discuss the interaction effects of dialect with other factors, and then turn to the main effect of dialect.

In the analysis of the results of the survey on existing words, five out of six significant interaction effects involve the dialect of the participants as summarized in (12). All the significant interaction effects of dialect and other factors in existing word data shown in (12) were either not tested or insignificant in the novel word data. Frequency and M₁ origin factors including their interactions with dialect were excluded from the novel word survey mainly due to the difficulty in creating appropriate test items. The remaining three interaction effects (12a–c) were tested in the novel word survey, but none of them turned out to be significant in the mixed effects logistic regression model presented in (16). It seems that the lack of statistical significance of the relevant dialectal differences in novel words might be due to the general reduction of average insertion rate in novel words, mentioned at the beginning of section 5.2.

Let us now compare existing and novel words with respect to the main effect of dialect. Recall that the average insertion rate was higher for Kyungsang speakers than Seoul speakers, regardless of whether test items were existing or novel Korean words. This might lead one to think that n-insertion is more likely to occur for Kyungsang speakers than Seoul speakers, and that the relevant lexical patterns were extended to novel words. However, given that the main effect of dialect was not significant in both statistical models for existing and novel word data, as presented in (8) and (16) respectively, neither Kyungsang speakers’ higher rate of insertion nor the consistency between existing and novel words can be ensured.

Note that the method of the present study has some limitations in detecting the dialectal difference even if the insertion rate is truly different between Kyungsang and Seoul Korean. First, a majority of Kyungsang participants employed in this study were relatively young, in their 20s (mean age = 25.9 years in existing word survey, 25.1 years in novel word survey). It is well-known in the literature on Korean linguistics that younger Kyungsang Korean speakers are more familiar with Seoul Korean than older Kyungsang Korean speakers. It is thus possible that the Kyungsang Korean participants in the current survey might, at least sometimes, have relied on their knowledge of Seoul Korean during the survey. Second, as pointed out by an anonymous reviewer, the modality of the task, i.e. text, not audio/production, might reduce the likelihood of finding dialectal differences. Given that non-standard dialects are usually used in spoken, as opposed to written, forms, it is possible that the modality of the present task prevented the Kyungsang participants from relying on their Kyungsang Korean grammar. Finally, as mentioned in section 3, all 304 test words used in the existing word survey were standard, thus Seoul, Korean words. The same set of test words was used for Kyungsang and Seoul Korean speakers for the purpose of making a direct comparison between the dialects. It might be then possible that Kyungsang Korean participants used their knowledge of Seoul Korean during the survey, at least when the test words were not in their native word lexicon. A more reliable detection of the dialectal difference under consideration can be made by employing older speakers of Kyungsang Korean as participants and spoken Kyungsang Korean words as test stimuli. This is left for future research.

To summarize, the present study found several statistically significant dialectal differences in the patterns of n-insertion in existing Korean words. However, it is still not known what other dialectal differences are active in existing words, and whether the dialectal differences in the lexicon can generally be extended to novel words.