2.1. Palatalisation

In Korean, coronal stops before high front vocoids (henceforth TI) become alveo-palatal affricates, as shown in (2a) and (2b). This palatalisation does not apply within morphemes, as shown in (2c), and thus it has been considered an instance of a derived environment effect.

Korean palatalisation applies obligatorily at stem–suffix boundaries, regardless of whether the suffixes are inflectional, as in (2a), or derivational, as in (2b) (Cho Reference Cho, Hanson and Inkelas2009: 466). This indicates that Korean palatalisation in morphologically derived environments is not only productive but also general.

In order to have a better understanding of the productivity and generality of palatalisation, we need to consider two complications involving other processes which may interact with palatalisation. First, the palatalised forms occurring before inflectional suffixes (2a) are not the only attested surface forms. In Korean, noun stem-final coronal obstruents are in variation mainly with [s] before vowel-initial suffixes. Thus, when noun stems ending in coronal stops are combined with /i/-initial suffixes, [s]-final variants may occur in addition to the palatalised forms, as shown in (3a). This stem-final obstruent variation is not limited to the palatalisation context, as shown in (3b) (see Jun Reference Jun2010 for more details of Korean noun stem-final obstruent variation).

Given that either palatalised forms or [s]-final variants, not [tʰ]-final forms, are attested in a palatalising context, as can be seen in (3a), we may consider palatalisation to apply obligatorily, and the resulting palatalised forms such as [pacʰi] may further be subject to free variation targeting stem-final obstruents, optionally yielding [s]-final forms such as [pasi]. Note that although innovative [s]-final forms may occur as free variants of the palatalised forms, none of the attested surface forms in the palatalisation context violate the palatalisation constraint. Thus, it is true that the palatalisation constraint, that is, *TI, is never violated across stem–suffix boundaries. This palatalisation, optionally followed by noun stem-final obstruent variation, is quite robust, and is extended to loanwords. When English words ending in stops are borrowed into Korean, either vowel epenthesis or final coda unreleasing applies: for example, Matt [mɛtʰɨ] \textasciitilde [mɛt˺] (personal name).Footnote ¹ Such loanword forms take different allomorphs of the nominative and accusative case markers, following a general allomorphic rule of Korean: vowel- and consonant-initial suffix allomorphs are used after consonant- and vowel-final stems, respectively. Specifically, when loanwords for English words ending in a coronal stop are inflected with nominative case markers, stem forms ending in an epenthetic vowel are suffixed with -ka (4a). In contrast, stem forms ending in an unreleased stop are suffixed with -i (4b). Here, stem forms before -i can end in either [cʰ] or [s], and thus sequences violating the palatalisation constraint, such as [tʰ-i], are unlikely to occur.Footnote ²

Note that because loanword stem forms with vowel epenthesis end in [tʰ], /tʰ/ can be considered as the underlying form of the loanword stem-final consonant in (4). Then, it is plausible to assume that [cʰ]-final forms occurring before -i are the result of applying palatalisation, and [s]-final forms occur due to the stem-final obstruent variation. This indicates that palatalisation, optionally followed by stem-final obstruent variation, applies to loanwords, confirming its high productivity.

The second complication is that TI sequences occurring in compounding and prefix–stem combinations usually undergo n-insertion, in which /n/ is inserted at the juncture of two morphemes when the first morpheme ends with a consonant and the following morpheme begins in a high front vocoid /i/ or /j/. This n-insertion is often optional, and thus TI sequences, which violate the palatalisation constraint, may surface, as shown in (5).Footnote ³ However, it seems that such non-palatalised forms are minor variants in the n-insertion context.Footnote ⁴

Consequently, it seems that there are no morphologically derived environments in Korean where the palatalisation constraint is violated frequently.

In summary, Korean palatalisation is highly productive at stem–suffix boundaries, and can also be considered general, given that it applies in all morphologically derived environments, except where n-insertion may apply.

2.2. Vowel harmony

To aid the understanding of Korean vowel harmony, let us first examine the vowel phoneme inventory of a dialect of Korean spoken in the Seoul-Gyeonggi area (henceforth, Seoul Korean), shown in (6).

This 10-vowel inventory can be considered a conservative one. The front rounded vowels /y/ and /ø/ are often diphthongised as [wi] and [we], respectively, surfacing faithfully only in some limited environments. In addition, it is controversial whether /e/ and /ɛ/ are merged completely or not. It seems true that the distinction between /e/ and /ɛ/ is completely lost at least among many younger speakers of Seoul Korean (see Lee Reference Lee1996 and Cho Reference Cho and Aronoff2016 for relevant discussion).

Korean has two types of vowel harmony, which hold in different domains: the inflection of verbs and adjectives (henceforth verbal inflection) and ideophones. The harmonic groups of vowels, traditionally called ‘light’ and ‘dark’, are different between the two vowel harmonies. The light vowel group consists only of /a o/ in the vowel harmony system of verbal inflection, as shown in (7a). In contrast, the light vowel group for ideophones is a larger set, as shown in (7b).

Since alternations involving vowel harmony occur only in verbal inflection, we will focus on the type of vowel harmony in verbal inflection in the remainder of this article.

In Korean, verb stems never occur in isolation; they are always suffixed. Verbal inflectional suffixes may be classified into the following four types, based on Choi (Reference Choi1985) and Kang (Reference Kang2006).

In Korean verbal paradigm, all vowel-initial inflectional suffixes have two basic allomorphs, [a]- and [ʌ]-initial, as illustrated in (9).Footnote ⁵

The choice between the two allomorphs depends on which harmonic group the last stem vowel belongs to. The specific selection mechanism is illustrated in (10).

[a]-initial forms are chosen when the last stem vowel is either /a/ or /o/, whereas [ʌ]-initial forms are chosen after any other stem vowel.

As discussed by Kang (Reference Kang2012: 7–12), in Middle Korean, vowel harmony was widely attested. Not only verbal but also nominal inflections showed harmonic alternations. Harmony also held within native Korean roots. Sino-Korean roots did not obey vowel harmony, but they constituted only a minority of the Middle Korean vocabulary (Kim Reference Kim2007). Thus, it is generally accepted that vowel harmony was pervasive and productive in Middle Korean. Since then, a variety of historical changes, such as vowel shift, vowel loss, monophthongisation, and the expansion of Sino-Korean vocabulary, have disrupted the vowel harmony system, resulting in its limited application in Contemporary Korean. Specifically, vowel harmony alternation takes place only in verbal inflection, not in nominal inflection.Footnote ⁶ In addition, there exist disharmonic root morphemes in the Korean lexicon, as shown in (11), and thus Korean vowel harmony can be considered an instance of derived environment effect.

Since Korean vowel harmony applies only in verbal inflection, it cannot be considered a general process. Moreover, even within verbal inflection, the domain of application of vowel harmony is subject to several further limitations. First, only vowel-initial, not consonant-initial, suffixes participate in vowel harmony: for example, /mʌk-A/ [mʌkʌ] *[mʌka] ‘eat-decl.ind’, but /mʌk-ca/ [mʌkc’a] *[mʌkc’ʌ] ‘eat-hort’ (where /A/ represents the underlying form of the alternating suffix-initial vowel).Footnote ⁷ Second, only the initial vowels of vowel-initial suffixes alternate due to vowel harmony, and non-initial suffix vowels have no harmonic variants, as can be seen in (9c) and (9d). Third, only the last vowel of the stem can trigger vowel harmony, and stem vowels other than the last one do not affect vowel harmony: for example, /k’apul-A/ [k’apulʌ], *[k’apula] ‘behave badly-decl’. Consequently, vowel harmony holds only between the last vowel of the verbal stem and the initial vowel of the following vowel-initial suffixes. Given that vowel harmony applies only in such a restricted domain, the generality of Korean vowel harmony is quite limited.

In order to ascertain how productive vowel harmony in Korean verbal inflection is, let us begin by considering which vowel, /a/ or /ʌ/, is the underlying form of the alternating suffix-initial vowel. Recall that [ʌ]-initial forms are used for a larger set of trigger stem vowels, that is, all vowels other than /a o/. This is not the only reason why /ʌ/ can be considered as the underlying vowel. The surface forms of the alternating suffixes not adjacent to the preceding stems provide more definite evidence for the underlying form of the suffix-initial vowel. As discussed above, vowel harmony applies only when the alternating suffixes are adjacent to stems. For instance, as shown in (12a), when the decl.ind suffix is immediately preceded by a stem with a light vowel /a o/, it is realised as [a]. In contrast, as shown in (12b), when the same suffix follows another suffix, it is always realised as [ʌ]. Note that the preceding suffix is realised as a light alternant, [as’], and thus the [ʌ]-initial form of the decl.ind suffix in (12b) cannot be due to vowel harmony. This clearly suggests that the underlying vowel of the decl.ind suffix is /ʌ/.

Given that it is possible that all attested [ʌ]-initial forms of the alternating suffixes are simply the underlying forms, it is only in [a]-initial suffix forms that we can be sure vowel harmony has applied.

Since vowel harmony shows exceptions and variations, [a]-initial suffix forms are not as frequent as expected when the last stem vowel is a light vowel /a o/, as experimentally shown in some previous studies on novel Korean words (Kang Reference Kang2012, Reference Kang2016; Jang Reference Jang and Erlewine2017) and as recently discussed and emphasised by Jo (Reference Jo2023). The most prominent exceptional pattern is that when the last stem vowel is /a/, disharmonic forms are attested often: for example, /mac-A/ [mac-a] \textasciitilde [mac-ʌ] ‘correct-decl’. Even more frequent exceptions occur when the stems are multi-syllabic p-irregular (in which stem-final /p/ appears as [w] before vowel-initial suffixes), regardless of whether the last stem vowel is /a/ or /o/: for example, /kølop-A/ [kølow-ʌ] (\textasciitilde[kølow-a]) ‘painful-decl’ and /alɨmtap-A/ [alɨmtaw-ʌ] (\textasciitilde[alɨmtaw-a]) ‘beautiful-decl’. Accordingly, the only case where vowel harmony is known to apply obligatorily is with regular verb and adjective stems with /o/ as the last stem vowel: for example, /nok-A/ [nok-a], *[nok-ʌ] ‘melt-decl.ind’. However, the results of some recent experimental studies on Korean vowel harmony (Kang Reference Kang2012; Jang Reference Jang and Erlewine2017) show that exceptional disharmonic forms occur even after novel stems with /o/ as the last stem vowel, and that the rate of vowel harmony in novel Korean words does not differ depending on the quality of the last stem vowel, whether /a/ or /o/. Thus, the exceptionless harmony pattern triggered by /o/ is not extended to novel Korean words.

Some quantitative information about how often Korean speakers apply vowel harmony in speech can be obtained from the results of Kang’s (Reference Kang2012) production experiment.Footnote ⁸ As shown in (13), in Kang’s experiment, exceptional disharmonic forms occurred much more often for novel Korean words than for real Korean words.

Furthermore, at least nine out of 30 Korean participants produced only [ʌ]-initial disharmonic forms for novel Korean stems with a light vowel, and additional six participants produced ʌ-initial forms for over 80% of the same novel stems (Kang Reference Kang2012: 51, Figure 20).Footnote ⁹ A similar pattern indicating complete loss of vowel harmony was observed in the results of Jang’s (Reference Jang and Erlewine2017) production experiment in which three out of 13 Seoul Korean participants produced only [ʌ]-initial forms for 12 verb stems with light vowels (four real and eight novel stems). Consequently, the results of the previous experimental studies using novel Korean words suggest that the true productivity of Korean vowel harmony is quite low, or even zero for some speakers.

In summary, Korean vowel harmony is neither general nor productive. The generality of vowel harmony is clearly limited in that it applies only between stem-last vowels and initial vowels of vowel-initial suffixes in verbal inflection. The productivity of vowel harmony is also limited since exceptions are frequent in existing words, and even more frequent in novel words.

2.3. Laryngeal OCP in compound tensing

For an effective illustration of phonation alternations in Korean compound tensing, let us start by examining the Seoul Korean consonant phoneme inventory, which is shown in (14).

Note that obstruents in Seoul Korean and many other dialects of Korean show three-way phonation contrasts between lenis, aspirated and tense. Among them, the laryngeally marked consonants (aspirated and tense) will be the focus of the current discussion.

In Korean, when a compound consists of two nouns, and the second noun stem (N₂) begins with a lenis obstruent, tensing can occur as shown in (15).

This tensing is often optional, and it shows lexical variation. One interesting tendency found in previous studies on Seoul Korean compound tensing (Zuraw Reference Zuraw2011; Kim Reference Kim2016) is the avoidance of tensing in words with laryngeally marked segments. Specifically, tensing is less likely when N₂ has tense or aspirated consonants, as in (15d) and (15e). This trend can plausibly be interpreted as the effect of laryngeal co-occurrence restrictions or laryngeal OCP. According to Ito’s (Reference Ito2014) study on compound tensing in Yanbian Korean (a variety spoken in China’s Yanbian Korean Autonomous Prefecture), this laryngeal OCP effect is more extensive in Yanbian Korean than in Seoul Korean, in that tensing is less likely even when the first component noun stem (N₁) has a laryngeally marked segment. Moreover, the laryngeal OCP effect that was found significant in existing compound nouns was mirrored in novel compounds. The laryngeal OCP effect has also been observed in Kang & Oh’s (Reference Kang and Mira2019) acceptability rating experiments for existing and novel Korean compounds, which employed speakers of Jeolla Korean (a variety spoken in the southwestern province of South Korea). Thus, it seems that the laryngeal OCP effect is active and productive in compounds in various dialects of Korean.

Note that there exist monomorphemes with multiple laryngeally marked consonants, as shown in (16), and thus the laryngeal OCP effect can be considered an instance of a derived environment effect.

Let us now consider how general and how productive the laryngeal OCP is in Korean. We are not aware of any morphological domains other than noun–noun compounding in which laryngeal OCP is active. In Korean, there are several tensing processes other than compound tensing which may create forms with multiple laryngeally marked onset consonants. First, post-obstruent tensing, in which a lenis obstruent becomes tense after an obstruent, is known to be an automatic process, and thus it is generally assumed to apply obligatorily. To the best of our knowledge, no previous studies report the blocking of post-obstruent tensing by the laryngeal OCP. In addition, the initial lenis consonants of adjective, noun and verb stems in Korean become tense optionally, as shown in (17).

The lexical meaning of adjectives and some nouns, but not verbs, can be intensified with this word-initial tensing. Kang & Oh (Reference Kang and Mira2016) collected (Jeolla) Korean speakers’ acceptability ratings on word-initial tensing by employing a set of real Korean words which do not undergo word-initial tensing. Based on their statistical analysis of the experiment results, Kang & Oh argue that word-initial tensing is preferred in words with tense consonants. This is the opposite of the laryngeal OCP effect.Footnote ¹⁰ Thus, the results of Kang & Oh’s experiment show no laryngeal OCP effect in word-initial tensing. Consequently, to the best of our knowledge, compound tensing is the only clear case, in which laryngeal OCP is effective in Seoul Korean and other dialects of Korean, and thus laryngeal OCP cannot be considered general in Korean.

Let us now consider how productive the laryngeal OCP is in Korean compound tensing. Note that tensing in compounding is variable, and laryngeal OCP decreases the tensing rate when stems have laryngeally marked consonants, as can be seen in (18a).Footnote ¹¹ Using the tensing rate data from the previous studies in (18a), we have calculated the rates of blocking by the laryngeal OCP, as shown in (18b).

The resulting rates of blocking in (18b) indicate that the blocking by the laryngeal OCP is far from obligatory in both Seoul and Yanbian Korean. This partial blocking effect is extended to novel compounds, as reported by the experimental studies on Yanbian Korean (Ito Reference Ito2014) and Jeolla Korean (Kang & Oh Reference Kang and Mira2019). Kang & Oh (Reference Kang and Mira2016) discuss their experimental results by providing mosaic plots and statistical tests, not detailed rates of compound tensing, and so we cannot calculate the rate of blocking of compound tensing using their published results. However, Kang & Oh clearly show that the presence of aspirated or tense onsets in N₂ do not completely block compound tensing, regardless of whether N₂ is real or novel, and that the blocking effect is higher in real compounds than in novel compounds. In summary, the results of the previous experimental studies on Korean compound tensing suggest that the laryngeal OCP blocks compound tensing, even when N₂ is a novel stem, but the blocking effect is only partial, not complete.

In this section, we have discussed how general and how productive the laryngeal OCP is in Korean. We may conclude that both generality and productivity of the laryngeal OCP effect are limited, since the effect is attested only in noun–noun compounding, and it is only partial, not even close to complete.

2.4. A summary

Based on the discussions presented in the previous sections, we may determine how the three alternation patterns in Korean differ in robustness which we consider to be a function of productivity (namely, rate of application) and generality (namely, breadth of application domain). It seems clear that Korean palatalisation is highly robust, given that both its productivity and generality are high. In contrast, Korean vowel harmony and laryngeal OCP are low in robustness, since they are limited in both productivity and generality, as summarised in (19).

The robustness summarised in (19) may lead us to make the following prediction based on the hypothesis in (1): in Korean, palatalisation will have more lexical support compared to vowel harmony and laryngeal OCP. To test this prediction, we conduct an acceptability rating experiment for non-words in §3 and a computational modelling of learning a phonotactic grammar in §4, modelled loosely on Daland et al. (Reference Daland, Hayes, White, Garellek, Davis and Norrmann2011).

3.1. Method

This section provides information about the stimuli, participants, and procedure utilised in the experiment.

4.1. Method

In order to construct a Seoul Korean lexicon, we first selected words listed as standard Korean in the Standard Korean dictionary (henceforth the SKD, National Institute of the Korean Language 1999; downloaded from https://stdict.korean.go.kr/mypage/download/downloadList.do on 17 September 2020). Among them, we further selected words with a frequency of at least one occurrence in the Sejong corpus. We extracted the citation-form pronunciations of the selected words from the SKD. In addition, we determined their morphological composition (simplex/complex) and etymological origin (native/Sino-Korean/loan) mainly based on the SKD. We prepared three monomorphemic word lexicons, not weighted by token frequency: (i) one with native Korean words ( $n = 5,335$ ), (ii) one with Sino-Korean words ( $n = 32,702$ ) and (iii) one with both native and Sino-Korean words ( $n = 38,037$ ).Footnote ¹⁹ Each of these was used as training data for modelling phonotactic grammars.

We conducted a simulation of learning a MaxEnt grammar by using UCLA phonotactic learner (Hayes & Wilson Reference Hayes and Wilson2008). The feature system fed to the learner was constructed mainly based on Cho (Reference Cho2012). Aspirated and tense consonants had different values for the feature [aspirated], but the two were specified as [+tense], thus forming a natural class. The feature [+spread glottis] was assigned only to /h/. Departing from Cho, we distinguished between onset and coda consonants by using the feature [rhyme], as in Daland et al. (Reference Daland, Hayes, White, Garellek, Davis and Norrmann2011) and Park (Reference Park2020). For the vowels, we adopted a nine-vowel system, /i e a ʌ o u ɨ y ø/, not distinguishing between /e/ and /ɛ/, which are known in the literature to be no longer contrastive, at least in younger Korean speakers’ speech. Although the front rounded vowels, /y ø/, are known to be diphthongised often, it is still possible that they are pronounced as monophthongs at least in some words, and thus we decided to adopt a conservative choice by distinguishing them in the vowel inventory. As recently discussed by Jun (Reference Jun and Aronoff2018), it is quite controversial what the feature involved in Korean vowel harmony is. A variety of features, such as backness, lowness, ATR and RTR, have been proposed. Given this indeterminacy, we specified /a o/ as [+RTR] and the rest of the Korean vowel phonemes as [−RTR], but make no theoretical commitment to this identification of the harmonising feature.

The learner settings were as follows. The length of constraint (i.e., the maximum gram size), the maximum number of constraints to discover and the highest O/E threshold were set at 2, 300 and 0.3, respectively.Footnote ²⁰ Constraints including complement natural classes (designated by the symbol \^~) were allowed to be found. Autosegmental tiers, called ‘projections’, were created and fed to the learner so that constraints for nonlocal processes like vowel harmony and laryngeal OCP could be found. Specifically, constraints can be defined on three different projections: (i) default segmental projection, that is, full representation; (ii) vowel projection, that is, the substring consisting of all and only vowels; and (iii) laryngeal projection, that is, the substring of all and only obstruent onsets. Palatalisation, vowel harmony and laryngeal OCP constraints were expected to be found from default, vowel and laryngeal projections, respectively. Finally, no prespecified constraints were fed to the learner.

4.2. Simulation results

The UCLA Phonotactic Learner creates phonotactic constraints through an inductive learning algorithm and assigns numerical weights to them according to the principle of maximum entropy (see Hayes & Wilson Reference Hayes and Wilson2008 for relevant details). If a form is underrepresented in the training data, a constraint prohibiting it will likely be learned. The more underrepresented a form is, the higher the weight of the constraint prohibiting it. To illustrate, some high-weighted constraints learned from the lexicon of native and Sino-Korean monomorphemes are shown in (30).

The two constraints in (30) reflect well-known phonological restrictions in Korean. In Korean, the velar nasal and true consonant clusters are not allowed at all in the onset.

The learner gave penalty scores to each test non-word depending on the weight of constraints violated by it and the number of violations, as defined by Hayes & Wilson (Reference Hayes and Wilson2008: 383, (4)). Note that such penalty scores (often called harmony scores) are known to match with human well-formedness intuitions (Breiss & Hayes Reference Breiss and Hayes2020: 362). For model predictions about acceptability of a non-word which will be compared to its human ratings, we used negative values of the penalty scores assigned to it which increase as acceptability increases like human ratings. Henceforth, the negative penalty scores will be referred to as ‘model ratings’. Since we trained the learner on three different lexicons, we were provided with three sets of model ratings.

Which lexicon and which set of model ratings should we rely on? We opt for the lexicon consisting of native and Sino-Korean monomorphemes, based on a plausible assumption, adopted by Chong (Reference Chong2019), that ordinary Korean speakers cannot reliably distinguish between native and Sino-Korean words. Still, since we were curious about whether and how the three lexicons differ in explaining the human ratings, we calculated the correlations (Spearman) between human ratings and each of the three sets of model ratings.Footnote ²¹ As can be seen in (31), the ratings given by the MaxEnt trained on both native and Sino-Korean words show the highest correlation with the human ratings although there is only a small difference between the lexicons consisting of only Sino-Korean words and both native and Sino-Korean words, which is not surprising if we consider the fact that the latter lexicon consists mostly of Sino-Korean words (85.97%, i.e., 32,702 out of 38,037).

In the remainder of this article, the set of native and Sino-Korean monomorphemes in our Seoul Korean corpus will represent the Seoul Korean lexicon, and the ratings given by a MaxEnt model trained on it will be referred to as ‘model ratings’.

As shown under ‘native and Sino-Korean’ in (31), the correlation between human and model ratings (0.73) is high. This high correlation between human and model ratings indicates that the Korean participants’ well-formedness judgements were heavily based on the frequency distribution of the Korean lexicon, confirming the assumption that speakers’ judgements are a good proxy for lexical phonotactics. In Figure 7, the human ratings for the entire test set of non-words, are plotted against the model ratings. (Human and model ratings for all test non-words are provided in the Supplementary Material.)

Figure 7

All test non-words: Correlation between human and model ratings (z-transformed; $n = 193$ ; dashed line = regression line).

The scatter plot in Figure 7 shows an overall trend that the human ratings increase as the model ratings increase, as is consistent with the high positive correlation between the human and model ratings, mentioned above.

Let us now consider how the correlations between human and model ratings differ depending on the stimuli. For each set of test stimuli, the correlation (Spearman) between observed human ratings, presented in the previous section, and the corresponding model ratings were calculated as shown in (32).

The correlation between human and model ratings is high for the non-words in the laryngeal OCP set, and moderate for the non-words in the palatalisation set. However, the correlation for non-words in the set of vowel harmony (0.20) is low. As will be shown below, the main reason for this relatively low correlation is that many of the non-words in the vowel harmony set were predicted to be rated as almost perfect, and thus the model rating values did not vary sufficiently, leaving little room for correlations with human ratings. In the following subsections, we discuss model ratings for each set of test non-words, testing the predictions from our research hypothesis in (1), and comparing them with the corresponding human ratings.

4.2.1. Palatalisation

In this section, we report and discuss the modelling results pertaining to palatalisation to test the specific predictions, shown in (33), which can be made from the hypothesis that Korean palatalisation, which is general and highly productive across morphemes, has strong lexical support.

• 

As shown in (34), the first prediction in (33a) seems to be confirmed since a general palatalisation constraint prohibiting TI sequences was learned in the current simulation, and its weight (3.286) is relatively high.

• 

The weight 3.286 is not as high as the weights of constraints reflecting exceptionless generalisations in Korean, for example, no velar nasal in the onset (6.605) and no true onset consonant clusters (7.682), as shown in (30). However, as will be shown below, it is much higher than the weights of any constraints with the effect of vowel harmony or laryngeal OCP.

The second prediction in (33b) is also confirmed by the model ratings in the violin plot in Figure 8.

Figure 8

Palatalisation: Model ratings of non-words, by CV sequence type. Crossbars represent mean ratings.

Note that target non-words with TI sequences are clearly lower in mean ratings than control non-words with TA and PI sequences. Recall that the observed lower ratings of non-words with TI sequences were also true for human ratings. The specific word-by-word correspondence can be seen in Figure 9, in which the human ratings for the palatalisation set are plotted against the model ratings.

Figure 9

Palatalisation: Correlation between human and model ratings ( $n = 66$ ; dashed line = regression line; filled circle = target with TI, empty triangle = control with TA, empty circle = control with PI).

Note that about half of the non-words with TI sequences, that is, target items (marked with filled circle) are located in the lower left quadrant of the plot, indicating that they are both predicted and judged to be ill-formed. Most of the control items with TA or PI sequences (marked with empty triangle and circle, respectively) are both predicted and judged to be better formed than the target items.

For a more accurate understanding of the current model ratings pattern, let us consider whether the model ratings differ depending on the specific target TI sequence. Recall that four TI sequences, /ti/, /tʰi/, /tj/ and /tʰj/, were used in the target non-words. As can be seen in Figure 10, non-words with no glide (/ti tʰi/) received higher ratings than those with a glide (/tj tʰj/). Among target non-words with no glide, those with a lenis onset (/ti/) received higher ratings than those with an aspirated onset (/tʰi/). Non-words with /ti/ were lower in mean ratings than control non-words with /tA/ and /Pi/.

Figure 10

Palatalisation: Mean model rating of target non-words with TI sequences and control non-words with tA and Pi. Smaller semitransparent points represent individual non-words, and larger points represent overall averages.

To provide a statistical analysis of the observed differences, we fitted a Bayesian linear regression model to the current model ratings data. Model ratings and consonant–vocoid sequence type – /ti/ (reference), /tʰi/, /tj/, /tʰj/, /tA/ and /Pi/ – were included as the dependent and independent variables, respectively. The consonant–vocoid sequence type was dummy coded. The results of the Bayesian analysis, presented in (35), suggest that it is likely true that the target non-words with /ti/ are rated higher than target non-words with /tj tʰj/, and that the target non-words with /ti/ were rated lower than control non-words with /tA Pi/, given that 95% CIs for the corresponding coefficients do not include zero. The sample distributions confirm all these conclusions, and, in addition, show that the posterior probability of the proposition that non-words with /ti/ are higher than those with /tʰi/ is 95.38%, suggesting that we can be 95.38% certain that items with /ti/ sequences are more well-formed than those with /tʰi/.

• 

The most important observation here is that model ratings of target non-words with /ti/, as well as other TI, sequences are meaningfully lower, compared to control non-words with /tA Pi/, confirming the prediction in (33b). This is in part consistent with the corresponding results of an acceptability-rating experiment, presented in §3.2.1. Recall that there is compelling evidence that the participants gave lower ratings to the non-words with /ti/ relative to /tA/, not /Pi/. Thus, it seems that the lexical support for palatalisation is even stronger in the MaxEnt simulation than in speakers’ phonotactic judgements. An additional discrepancy between model and human ratings for non-words in the palatalisation set can be seen; the difference between non-words with /tʰi/ vs. /tj tʰj/ is larger in model ratings than in human ratings. This might be in part due to a floor effect in which the human ratings were already low for non-words with /tʰi/ (2.44), and so the participants could not give much lower ratings for non-words with /tj tʰj/.

In conclusion, the two predictions in (33) are confirmed by the results of the current simulation, indicating that lexical items with TI sequences in the Korean lexicon are underrepresented, and thus that general and productive cross-morphemic palatalisation in Korean has strong lexical support.

4.2.2. Vowel harmony

In this section, we report and discuss the modelling results pertaining to vowel harmony to test the specific predictions presented in (36) which can be made from the hypothesis that Korean vowel harmony with limited generality and productivity has no, or weak, lexical support.

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To test the prediction in (36a), we investigated the vowel projection constraints learned in the current simulation. All vowel projection constraints learned either were trivial (such as *## ‘no word without a vowel’) or else involved front rounded vowels [y ø] or the high back unrounded vowel [ɨ], all of which have highly limited distributions in Korean. Note that none of these vowels were used in the current set of non-words. What is important here is that no vowel harmony constraints prohibiting disharmonic vowel sequences were learned, confirming the prediction in (36a). This indicates that disharmonic vowel sequences are not underrepresented in the Korean lexicon.

To test the second prediction in (36b), we investigated the distribution of model ratings of the non-words in the vowel harmony set. As can be seen in Figure 11, the mean model ratings are slightly higher for disharmonic non-words than for harmonic ones, thus confirming the prediction in (36b).Footnote ²²

Figure 11

Vowel harmony: Model ratings of Korean non-words, by the type of vowel sequence (disharmonic vs. harmonic). Crossbars represent mean ratings.

Recall from §3.2.2 that higher scores for disharmonic words were also found in the human ratings. The specific word-by-word correspondence can be seen in Figure 12, in which the human ratings for the vowel harmony set are plotted against the model ratings.

Figure 12

Vowel harmony: Correlation between human and model ratings ( $n = 80$ ; dashed line = regression line; filled circle = disharmonic, empty circle = harmonic).

Note in Figure 12 that many items, either disharmonic (filled circle) or harmonic (empty circle), were located near the high end of the model rating scale. Specifically, as shown in (37), the majority of the test items in the vowel harmony set (68 out of 80 items) were predicted to be perfect (i.e., 0) or near-perfect (i.e., $-1.62$ and $-1.69$ ). The limited variation due to the dominance of such (almost) perfectly well-formed non-words can explain why the correlation between human and model ratings was relatively low (0.20) for the non-words in the vowel harmony set, presented in (32).

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In conclusion, the two predictions in (36) are confirmed by the results of the current simulation, indicating that lexical items with disharmonic vowel sequences in the Korean lexicon are not underrepresented, and thus that Korean vowel harmony with limited generality and productivity has no lexical support.

4.2.3. Laryngeal OCP

In this section, we report and discuss the modelling results pertaining to laryngeal OCP to test the specific predictions presented in (38) which can be made from the hypothesis that laryngeal OCP in Korean with limited generality and productivity has no, or weak, lexical support.

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To test the first prediction in (38a), we investigated the laryngeal projection constraints learned in the current simulation. No general laryngeal OCP constraint (i.e., *[+tense][+tense]) was learned. However, two of the three constraints learned on the laryngeal projection, (39a) and (39b), express more specific laryngeal OCP generalisations. In (39a) *[+tense][+aspirated], with a weight of 1.256, penalises aspirated–aspirated and tense–aspirated onset sequences, and in (39b) *[+aspirated][−aspirated,+tense], with a weight of 0.564, penalises aspirated–tense onset sequences. No constraint prohibiting tense–tense sequences was learned on the laryngeal projection. In summary, relatively low-weighted laryngeal OCP constraints were learned only for some potential target sequences, which we may consider to be consistent, at least in part, with the prediction in (38a). The set of learned laryngeal OCP constraints and their weights suggest that only some of onset sequences violating the laryngeal OCP are weakly underrepresented and the rest are not underrepresented in the Korean lexicon. This may indicate that laryngeal OCP in Korean compounding has weak lexical support.

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To test the second prediction in (38b), we investigated the distribution of model ratings of the non-words in the laryngeal OCP set. The model ratings differ for non-words with different numbers of laryngeally marked consonants, as shown in Figure 13.

Figure 13

Laryngeal OCP: Model rating in the MaxEnt simulation by number of laryngeally marked consonants.

Note in Figure 13 that as the number of laryngeally marked consonants increases, the model ratings decrease, with the double-lar non-words being predicted to have the lowest ratings. Recall from §3.2.3 that the observed hierarchy, no-lar > single-lar > double-lar, was also true for human ratings. The more specific word-by-word correspondence can be seen in Figure 14, in which the human ratings for the laryngeal OCP set are plotted against the model ratings.

Figure 14

Laryngeal OCP: Correlation between human and model ratings ( $n = 75$ ; dashed line = regression line; empty circle = no-lar ( $n = 8$ ); grey circle = single-lar ( $n = 35$ ); black circle = double-lar ( $n = 32$ )).

Note that many of the double-lar items, that is, target items (marked with black circles), are located in the lower left quadrant of the plot, indicating that they are both predicted and judged to be ill-formed. Among control items, all eight no-lar items (marked with empty circles) are located at the upper right quadrant of the plot, indicating that they are both predicted and judged to be well-formed, whereas single-lar items (marked with grey circles) show an intermediate pattern between double and no-lar items, covering a relatively wide range.

In order to have a more accurate and better understanding of the ratings pattern under consideration, let us consider how the patterns differ depending on the specific phonation type of an onset consonant. From Figure 15, in which model ratings of test non-words are plotted by the onset type, we can make some observations. First, single-lar items are not as good as no-lar items, as we have seen in Figure 13. Second, single-asp items are higher in model ratings than double-asp (and all other double-lar) items. Third, single-tense items are higher in model ratings than double-tense (and tense//asp) items, but lower than double-asp items. Thus, having one tense onset is already quite bad in the simulated grammar, as is also the case in the human judgements presented in §3.2.3. As we can see by comparing Figure 6 and Figure 15, one notable difference between human and model ratings is that the differences between single-tense vs. double-tense and tense//asp items are smaller in human ratings than in model ratings, which can be attributed to a floor effect.

Figure 15

Laryngeal OCP: Model rating in the MaxEnt simulation, by the onset type.

As we have done in §3.2.3, let us now check whether there is a superadditive effect, focusing on the modelling results for double-lar items with at least one tense onset, that is, double-tense and tense//asp. If double-tense items are subject to laryngeal OCP, the reduction in ratings from single-tense to double-tense items would be larger than the reduction from no-lar to single-tense items. This predicted superadditivity effect did not occur, as can be seen in (40).

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If tense//asp items are subject to laryngeal OCP, the reduction in ratings from no-lar items to tense//asp items would be larger than the sum of the reductions from no-lar to single-tense items and from no-lar to single-asp items. This predicted superadditivity emerged, as can be seen in (41).

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Thus, only non-words with tense//asp, not double-tense, sequences show a superadditive effect in mean model ratings, which is consistent with the laryngeal OCP constraints in (39a) and (39b), learned in the MaxEnt simulation. However, the evidence for a superadditive effect in (41) is not compelling, according to the results of a Bayesian linear regression model analysis (not shown), in which model ratings and the onset consonant type were included as the dependent and independent variables, respectively. The sample distributions show that the posterior probability of the proposition that Δ(no-lar, tense//asp) > Δ(no-lar, single-tense) + Δ(no-lar, single-asp) is only 90% (where Δ(A, B) represents the difference between A and B). Consequently, model ratings data indicate that the laryngeal OCP is not active in the Korean lexicon.

In summary, the results of the MaxEnt simulation indicate that only some subsets of potential target sequences of laryngeal OCP are possibly slightly underrepresented in the Korean lexicon, since co-occurrence constraints were learned only for those subsets (and with relatively low weights), not for the rest of the target sequences, and model ratings for double-lar non-words show no compelling evidence for superadditivity, which is predicted to occur under the hypothesis that laryngeal OCP is active in the Korean lexicon. These results lead us to conclude that the laryngeal OCP in Korean has no, or possibly weak, lexical support.