Like other experiments reviewed above, our research examines the learning of miniature artificial languages differing in the magnitude of base changes they require. In particular, we examined how easy it is to learn to palatalize voiced and voiceless labial, alveolar, or velar stops before -i. All experimental conditions had the same output forms (namely, plurals that ended in -tʃi), but differed in the magnitude of the change required to get from the singular to the plural. Yun (2006) showed that English alveopalatals involve both a tongue body gesture, similar to that of a velar, and a tongue blade gesture, similar to that of an alveolar. In contrast, labials do not share any oral gestures with alveopalatals. Therefore, in articulatory terms, labial palatalization is a larger change than alveolar or velar palatalization and involves saltation over either [t] or [k], depending on whether one reaches [dorsal & coronal] from [labial] through [dorsal] or [coronal].

Typologically, palatalization of coronals and velars is about equally common, while palatalization of labials is extremely rare (Bateman, 2007; Bhat, 1978; Chen, 1973; Kochetov, 2011). Kochetov (2011) proposes an implicational universal: Labial palatalization implies palatalization of coronals and/or velars, while Bateman (2007) suggests that there are no clear cases of productive labial palatalization in which the labial articulation is fully suppressed in the palatalized outcome. Typological frequency often maps onto how easy a pattern is to learn (e.g., Finley, 2008; Mitrović, 2012; Schane, Tranel, & Lane, 1975; White, 2013, 2014; White & Sundara, 2014; Wilson, 2006). The typological data thus strongly suggest that there may be a learning bias against labial palatalization, which may cause labial palatalization to either not be learned or to be overgeneralized to coronals and/or velars, resulting in patterns obeying the implicational universal.

The present work follows up on preliminary results previously reported in a proceedings paper (Stave, Smolek & Kapatsinski, 2013). In this previous work, we also exposed participants to one of three different palatalization patterns: p➔tʃ, k➔tʃ, or t➔tʃ, but palatalization was triggered by -a, and did not occur before -i. This was to show that an observed bias against changing some consonants could not be attributed to high markedness of unchanged consonants in the change-triggering context. We found that the differences in palatalization rates between the to-be-palatalized consonant and the not-to-be-palatalized consonants were significantly smaller in the group trained on p➔tʃ than in the other groups, despite the fact that there is nothing particularly marked about [pa]. The interaction appeared to be driven both by a lower palatalization rate for to-be-palatalized labials compared to to-be-palatalized alveolars and velars and by increased palatalization rates for not-to-be-palatalized consonants in the labial condition. However, neither of the individual effects reached significance. Judgment data showed a trend towards the same interaction but it was not statistically significant.

In the present study, we replicate Stave et al. (2013) using palatalization before [i], rather than [a], a more natural context that we hoped would make palatalization easier to learn (Mitrović, 2012; Wilson, 2006). In this context, palatalization of [t] and [k] is also plausibly driven by the markedness of [ti] and [ki]. Examining palatalization before -i therefore lets us test whether the bias against labial palatalization observed cross-linguistically in natural contexts (Bateman, 2007; Kochetov, 2011) is driven by the low markedness of [pi] compared to [ti] and [ki]. We also changed the distribution of the palatalizing and non-palatalizing suffix across consonants, with the aim of increasing the experiment’s power to detect differences in palatalization rates across conditions. The languages in Stave et al. (2013) used the palatalizing suffix 50% of the time each with the to-be-palatalized stems, and 100% of the time elsewhere. The present languages reverse these proportions, so that the palatalizing suffix is favored rather than disfavored by to-be-palatalized consonants. The aim of this change was to increase the number of instances of palatalization in the appropriate context in two ways. First, we hoped for an increase in the use of the palatalizing suffix with to-be-palatalized consonants: Participants tend to match suffix probabilities, at least in the aggregate (e.g., Kapatsinski, 2010). Second, Kapatsinski (2010) showed that exposing participants to many examples of a suffix simply attaching to a stem without changing it reduces the productivity of changes triggered by the suffix. For example, experiencing many examples of t➔ti and p➔pi reduces the productivity of k➔tʃi relative to k➔ki. We hoped to maximize the productivity of palatalization by ensuring that the palatalizing suffix changes the stem it attaches to more often than not.

In our experiment, participants were placed in either Labial, Alveolar, or Velar Palatalization conditions, which contained the corresponding palatalization pattern, as illustrated in Table 1. Singulars were always C(C)VC forms ending in oral stops. Plurals were formed by adding the plural suffixes -i and -a. Depending on the condition to which a participant was assigned, either labial, alveolar, or velar stops were palatalized, becoming [tʃ] if voiceless and [dʒ] if voiced. (The voiced varieties were included to test for the effect of articulatory vs. perceptual similarity, a question that is outside the scope of the present paper.) We consider labial palatalization to be saltatory because it involves changing a labial into a sound that involves both coronal and dorsal articulations (Yun, 2006).

Participants’ knowledge of the language was tested using elicited production and judgment tests requiring generalization to novel singulars. The production test involved hearing a novel singular and saying the corresponding plural form. The judgment test involved hearing singular-plural pairs and judging whether the plural form is the right one for the singular form.

As discussed above, our basic expectation was that labial palatalization—a large saltatory alternation—would be harder to learn than alveolar or velar palatalization. In particular, we expected the p~tʃ alternation to be more difficult to produce after training than the k~tʃ and t~tʃ alternations. In addition, if saltatory alternations overgeneralize to intermediate sounds and [tʃ] is both coronal and dorsal while [p] is neither, labial palatalization should be taken to imply either velar or alveolar palatalization but not vice versa. We now describe a number of more specific hypotheses we evaluate. These hypotheses are used to structure the results section.

Hypothesis 1: Labial palatalization is hard to learn because of faithfulness, not markedness. Judgments of unfaithful mappings will differ across conditions but judgments of faithful mappings will not. In other words, p~tʃ is worse than k~tʃ or t~tʃ but k~ki and t~ti are as good as p~pi. This finding must hold for us to argue that the bias against labial palatalization is a bias against certain alternations rather than against certain structures the alternations repair (e.g., Gnanadesikan, 1997; Kirchner, 1996; Steriade, 2001/2009; White, 2013). If Hypothesis 1 does not hold for our data, any condition differences we obtain may be due to markedness differences between [pi] on the one hand and [ti] and [ki] on the other, the structures repaired by palatalization. In particular, if [ki] and [ti] are worse (i.e., more marked) than [pi], palatalization of [t] and [k] is expected to be easier to learn than palatalization of [p] on these grounds alone (Pater & Tessier, 2006).

Hypothesis 2: Large alternations are hard to produce. If alternation magnitude influences learnability, labial palatalization should be harder to learn than alveolar or velar palatalization. In particular, if large alternations (of which saltation is one example) are hard to learn to produce (Skoruppa et al., 2011), [p] should be palatalized less in the Labial condition than [t] is palatalized in the Alveolar condition or [k] is palatalized in the Velar condition.

Hypothesis 3: Saltatory alternations are likely to be overgeneralized. If saltatory alternations are especially likely to be overgeneralized (Hayes & White, 2015; Moreton & Pater, 2012a; White, 2013, 2014, 2017; White & Sundara, 2014), the same not-to-be-palatalized consonants should be palatalized more in the Labial condition than in the other conditions. For example, [t] might be palatalized more often when participants are trained on p➔tʃi than when they are trained on k➔tʃi.

Hypothesis 4: Large changes are hard to produce even if judged to be preferable. The difference between the Labial condition and the other conditions should be greater in the production test than in the judgment test. Particularly, we hypothesized that labial palatalization may be rarely produced even when judged to be more acceptable than lack of palatalization. This expectation was based on a small-scale experiment reported by Zuraw (2000). Zuraw found that Tagalog speakers seldom produced nasal substitution, which requires a change to the base, but judged it to be more acceptable than nasal assimilation, which does not require a stem change. This dissociation between judgment and production would also address the possible criticism that judgments are simply more tolerant than production (e.g., Kempen & Harbusch, 2005) by showing that the less acceptable alternative is more likely to be produced. In other words, it would indicate that the speaker recognizes that the form that results from an alternation is the right thing to say without quite having the ability to say it.

One hundred seven undergraduate students in introductory psychology or linguistics courses at the University of Oregon were recruited through the Human Subject Pool and received partial course credit for participation. Eleven subjects were excluded for producing plurals that did not correspond to the patterns in the training. This left 32 subjects in the Alveolar condition, 31 in the Labial, and 33 in the Velar. All reported being native speakers of English, with no speech, hearing, language, or learning disabilities.

In every condition, there were 28 unique singular forms of words, which were randomly paired with Spore creatures selected from the database of user-created images at sporepedia.com. Each creature was shown at least once alone, and at least once as part of a group (the same image copied and pasted multiple times); the images containing a single creature were accompanied by a recording of the singular form, and the images containing groups of creatures were paired with the corresponding plural form (see Figure 1 below for illustration). All word-picture pairings appeared in random order, so the corresponding singulars and plurals were rarely temporally adjacent. In previous work (Kapatsinski, 2012), this ordering was found to encourage overgeneralization compared to presenting singular-plural pairs, presumably by making it less obvious which singular-final consonants map onto [tʃ] and [dʒ].

The singular forms for all tokens were single-syllable roots of C(C)VC structure, where the word-final consonant was an oral stop. Twelve out of the 28 training words ended with the to-be-palatalized consonants (Alveolar contained 6 each of stems ending with [t] and [d], Labial of [p] and [b], and Velar of [k] and [g]), with the remaining 16 split evenly between the other two place*voice combinations. Stimuli are shown in the appendix.

Note that participants were presented with the same amount of training regardless of whether they were trained on labial, alveolar, or velar palatalization. This contrasts with some previous work, which has trained participants to criterion or excluded low performers (White, 2013, 2014). We believe that these procedures obscure the nature of the bias against large changes by ensuring that participants learn the trained alternations equally well.

For the production test portion of the experiment, we selected an additional 92 creatures from the Spore Creature Creator database. As before, we copied and pasted the creatures such that, for each creature, there was one slide showing a single creature and one slide showing a group of creatures. The singular slide was again accompanied by the recording of the singular form, but the plural slide played no recording. Instead, subjects were told to say what they thought the plural form for the singular should be, which we recorded for later coding. Thirty-six of the 92 singulars ended with the consonants subjects had been trained to palatalize (half voiced, half voiceless), with the remaining 56 split evenly between the other places and voicing.

Each plural recording from a subject was saved as a separate file and coded by either the first author or undergraduate RAs, whose codings were all checked by the first author for accuracy. In case of inter-coder disagreement, the first author re-listened to the file and coded it appropriately; in the rare case that the production was unclear, the spectrogram was examined. We coded in particular for the stem-final consonant and the word-final vowel in the plural form. If a participant replaced the stem-final consonant with either of the palatals (e.g., blaɪp → blaɪtʃi), we coded the form as being palatalized; if the participant retained the same consonant in the plural (e.g. blaɪp → blaɪpi), the form was coded as not palatalized. If the stem consonant was retained but the palatal was also added (e.g., blaɪp → blaɪptʃi), we also categorized the form as not palatalized. While these products fit the “plurals should end in tʃi” schema, they preserve the final consonant of the base, underapplying the alternation. Biases to preserve aspects of the base should therefore favor these kinds of plurals alongside plurals like blaɪp → blaɪpi. Because these ‘blend’ Ctʃi responses are relatively rare, the results are unchanged if they are omitted or coded as palatalized instead. Rarely, a subject would replace the stem consonant with another non-palatal (e.g. blaip → blaida); such responses are excluded from all analyses. Instances where subjects added the English plural -s were also excluded, and subjects who produced a majority of such responses were excluded entirely.

Since the judgment task exposes participants to plural forms that contradict training, it followed the production task. The judgment session was the same across all conditions. Thirty new singulars were created, divided equally between the three places and two voices. For each singular, we recorded four plural forms, crossing whether the final consonant was palatalized and whether the suffix was -i or -a (e.g., for the alveolar stem prut, the plural forms were pruti, pruta, prutʃi, and prutʃa). For each ratings trial, the picture of a single creature appeared first with the recording of the singular form, followed by a picture of a group of the same creatures with the recording of one of the plural forms.

Subjects were instructed to indicate, using a button box, whether the plural form they heard was the right plural form for the singular. Each subject received a different random order of the 120 singular-plural pairings.

The button box had five buttons but the participants’ responses were strongly bimodal: 59% of the ratings were either ‘1’ or ‘5,’ 29% were ‘2’ or ‘4,’ and only 12% were ‘3.’ Because of this, and for comparison with the inherently binary production task data, we transformed the obtained ratings into binary dependent variables. See Appendix B for analyses using untransformed data. Two such variables were created:

The Absolute Judgment variable allows us to examine the effects of condition on judgments of palatalization and faithful mappings separately. This is essential to evaluate Hypothesis 1, that the observed bias is driven by faithfulness rather than markedness. Previous studies of the bias against saltation (except for our preliminary data in Stave et al., 2013) have forced participants to choose between a faithful and an unfaithful form by using production or forced choice tasks, which does not allow the experimenter to distinguish between a preference for one form and a dislike of the other (when given the singular blup and the plural options blupa and blutʃa, they may choose blupa because they really like it, or because they really dislike blutʃa; see Kapatsinski, 2007, for discussion).

The Relative Judgment variable was originally created to compare judgment to production. It embodies the assumption that palatalization is produced when it is more acceptable than lack of palatalization. However, there were no effects of training condition on judgments of faithful mappings. Consequently, the results are the same whether Absolute or Relative Judgments are used, and only the more informative Absolute Judgment data are reported below.

While some readers may be concerned that 3’s were excluded from the binary judgment analysis, the distribution of 3’s is equivalent across training conditions and final consonant place (Figure 2; for training conditions: F(2) = 1.33, p = 0.26, ns, left panel; for final consonant place: F(2) = 0.98, p = 0.38, ns, right panel), and all results reported below are the same regardless of whether binarized ratings or the full rating scale is used. As such, we report the results of the analyses based on absolute judgments in the text for ease of comparison to production, and the results using the untransformed rating scale in Appendix B.

All statistical analyses were conducted using generalized (logistic) linear mixed-effects models by means of the lme4 package (version 1.1–9, Bates et al., 2015) in R (version 3.1.1, R Development Core Team, 2014). We included fixed effects for Training Condition (contrast coded as noted for each model), Plural Vowel (-i vs -a), Test Place (Labial, Alveolar, Velar), To-Be-Palatalized Place (To-be-palatalized vs. Not-to-be-palatalized given the training), Test Voice (Voiced vs. Voiceless), Test Type (Production vs. Judgment), and interactions as applicable. Random intercepts were included for Subjects and Bases, and we used the full random effect structure that would allow our models to converge. Log likelihood tests on nested models were used to derive significance values. When a contrast was not significant, and this null result was expected under some hypothesis, evidence for the null hypothesis was evaluated using the BIC approximation to the Bayes Factor (Wagenmakers, 2007). The BIC approximation to the Bayes Factor compares the posterior probabilities of the null and alternative hypotheses under the assumption that their prior probabilities are equal. Unlike a frequentist analysis, it can therefore provide positive evidence in favor of the null hypothesis, distinguishing between ‘lack of evidence against the null’ and ‘evidence for the null.’ Tested models are presented in the notes. The full dataset and analysis code are available as additional files below.

Before we turn to determining whether there is a bias against p~tʃ, we would like to evaluate whether any such bias could be explained as a side effect of the markedness of [ti] and [ki] compared to [pi]. Perhaps [t] and [k] are easy to change into [tʃ] compared to [p] before [i] because participants come to the experiment ready to avoid [ti] and [ki] but have no pre-existing aversion to [pi]. We can evaluate this possibility using the absolute judgments of faithful mappings in the judgment test. If there is a bias against [ti] and/or [ki], we would expect judgments of p~pi in the Labial condition to be higher than judgments of t~ti in the Alveolar condition or k~ki in the Velar condition. However, Figure 3 shows no significant difference in ratings of no-change plurals for to-be-palatalized consonants across conditions1 and, if anything, a slight trend in the unexpected direction for not-to-be-palatalized consonants,2 which is also not significant (Tables 2 and 3). According to the BIC approximation to the Bayes Factor, these results provide very strong evidence for the null hypothesis (ΔBIC = 14.1, P_BIC (H₀|D) = 0.999). These results are inconsistent with the markedness explanation: The bias is against certain changes, not against certain output structures. In addition, they show that subsequent analyses can continue to utilize absolute rather than relative judgments as the dependent variable: Any between-condition differences in relative judgments would be driven by differences in absolute judgments of alternations rather than of faithful mappings.

Each bar in Figure 4 represents the rate of palatalization in production for the to-be-palatalized consonants (light bars) and not-to-be-palatalized consonants (dark bars). Bars are grouped by training language, which determines the identity of the to-be-palatalized consonants. For example, after exposure to the Labial language, the to-be-palatalized consonants are labial. According to Hypothesis 2, to-be-palatalized consonants should be palatalized less often when the palatalization would require a large change to the base, i.e., in the Labial condition. Figure 4 shows that there is a large difference between the Labial condition and the lingual conditions in the expected direction: To-be-palatalized labials are palatalized dramatically less often than to-be-palatalized alveolars or velars. Participants learned to palatalize velars when trained on velar palatalization, and alveolars when trained on alveolar palatalization. However, they did not learn to palatalize labials any more than non-labials when exposed to labial palatalization. In fact, participants exposed to labial palatalization palatalized labials slightly less than non-labials. These differences are largely due to how often the to-be-palatalized consonants are palatalized (light bars), as expected under Hypothesis 2, rather than in how much palatalization is overgeneralized to the not-to-be-palatalized consonants (Hypothesis 3). These results replicate Skoruppa et al. (2011) and contradict White (2013).

Statistically, we observe that to-be-palatalized base consonants are palatalized significantly less often (i.e., retained significantly more often) in the Labial Palatalization condition relative to the Alveolar and Velar Palatalization conditions (Table 4),3 with no overall effect of voicing and no interactions with voicing. Training Condition significantly improved the fit of the model, χ²(2) = 29.47, p < 0.001.

Hypothesis 2, a bias against changing labials into alveopalatals, predicts that labials will be palatalized less than the linguals both when they should be palatalized, and when they should not be palatalized. The first half of the claim is confirmed by Figure 4 and Table 4. The second half of the claim is confirmed by the data in Figure 5 and Tables 55 and 66: Labials are palatalized in error less than other stops are palatalized in error; overgeneralization to labials is shown in dark bars and overgeneralization to linguals in light bars.

To summarize the results so far, the data strongly support a bias against labial palatalization in production. There is a lower rate of palatalization for both the (to-be-palatalized) labials in the Labial training condition and the (not-to-be-palatalized) labials in the other training conditions. In other words, participants are less likely to palatalize labials than linguals, whether correctly or in error.

In order to evaluate this hypothesis, we ask whether alveolars are palatalized more when participants are trained to palatalize labials than when they are trained to palatalize velars. Similarly, are velars palatalized more when participants are trained to palatalize labials than when they are trained to palatalize alveolars? If alveopalatals are [dorsal] and [coronal] (Yun, 2006), then changing a labial into an alveopalatal involves changing both features and therefore saltation over either [t] or [k], depending on the route taken. In contrast, a change from the [dorsal]-only [k] to [dorsal;coronal] does not involve saltation over a [coronal]-only sound, [t]. Similarly, a change from [coronal]-only [t] to [coronal;dorsal] does not involve saltation over [k]. Thus, labial palatalization should overgeneralize to velars and alveolars but velar and alveolar palatalization need not support each other.

Contrary to Hypothesis 3, there was no significant difference in palatalization rates of alveolars between the Labial and Velar training conditions7 (b = –0.46, se(b) = 0.68, z = –0.67, p = 0.50). Likewise, there was no significant difference in palatalization rates of velars between the Labial and Alveolar training conditions8 (b = –0.46, se(b) = 0.67, z = –0.69, p = 0.49); see Figure 6. Furthermore, based on the BIC approximation to the Bayes Factor, the results provide strong evidence for the null hypothesis in both cases: ΔBIC = 6.9, P_BIC (H₀|D) = 0.97 and ΔBIC = 7, P_BIC (H₀|D) = 0.97, respectively. In other words, the present study had sufficient power to provide positive evidence in favor of the null hypothesis that overgeneralization is no more likely with a saltatory change than with a non-saltatory change (contra White, 2013, 2014).

In the judgment data, subjects trained on Labial and Alveolar Palatalization did not differ in their judgments of k➔tʃ overall9 (b = –0.02, se(b) = 0.31, z = –0.70, p = 0.94, ns) or in the palatalizing context, before -i10 (b = –0.40, se(b) = 0.44, z = –0.91, p = 0.36, ns); based on the BIC approximation to the Bayes Factor, there is strong evidence for the null across suffixes (ΔBIC = 6.8, P_BIC (H₀|D) = 0.97) and positive evidence before -i (ΔBIC = 5.4, P_BIC (H₀|D) = 0.94). Figure 7 shows the acceptability of k➔tʃ by training language across suffixes and before -i.

Velar and Labial training conditions did not show a difference in judgments of t➔tʃ across suffixes11 (b = –0.63, se(b) = 0.39, z = –1.59, p = 0.11, ns. According to the BIC approximation to the Bayes Factor, the results are positive evidence for the null hypothesis (ΔBIC = 4.4, P_BIC (H₀|D) = 0.90). In the palatalizing context, subjects trained on velar palatalization gave ‘marginally’ lower ratings of palatalized alveolars than those trained on labial palatalization (b = –0.89, se(b) = 0.47, z = –1.86, p = 0.06; Trained Place marginally improves model fit, χ²(1) = 3.40, p = 0.06). This trend is in the direction consistent with greater overgeneralization in the Labial condition. However, according to the BIC approximation to the Bayes factor, the results are still more consistent with the null than with the alternative hypothesis, ΔBIC = 2.78, P_BIC (H₀|D) = 0.80). Figure 8 shows the acceptance rates of t➔tʃ after Labial and Velar training.

Overall, there is little evidence that saltatory alternations are especially likely to be overgeneralized, even in a judgment task. In any case, the difference in likelihoods of overgeneralization between saltatory and non-saltatory alternations is quite small, compared to the very large differences in productivity reported in Figure 4.

We suspected that the bias against labial palatalization should be stronger in production than in judgment. Since the judge is presented with the palatalized output form, whatever difficulty they would face generating the form is alleviated (see also Harmon & Kapatsinski, 2017; Luce & Pisoni, 1998, for similar arguments regarding the difference between open-set and closed-set tasks).

As we saw in Figure 2 above, ratings of faithful plurals do not differ across conditions. Thus, any judgment differences between conditions we could see must come from judgments of unfaithful forms featuring palatalization. These data are shown in the left panel of Figure 9, side by side with production data from Figure 4 repeated here in the right panel.

Table 7 reports a mixed-effects regression model comparing the patterns of results across the two panels of Figure 9. The dependent variable for the model in Table 7 was binary, with 0 corresponding to production of a non-palatalized form in the production task and a rejection (rating < 3) of a palatalized form in the judgment task; 1 corresponded to production of a palatalized plural in the production task and acceptance (rating > 3) in the judgment task. The comparison reveals several findings. First, there is a striking dissociation between production and judgment after exposure to labial palatalization (left bars): Labial palatalization is typically accepted but not produced (as shown by the significant interaction in Table 7,12 which significantly improves the fit of the model, χ²(1) = 21.94, p < 0.001). This dissociation between judgments and production is not present for training on alveolar and velar palatalization: When trained to palatalize alveolars or velars, participants produce palatalization as often as they accept it; when trained to palatalize labials, they accept palatalization but do not produce it.

One might argue that judgments are simply more lenient than production, hence speakers accept more than what they would produce (e.g., Kempen & Harbusch, 2005). However, a comparison of incorrectly faithful to-be-palatalized and correctly palatalized plurals, as shown in Figure 10 below, shows that this explanation is insufficient to account for the present data. Judgments of faithful p➔pi mappings are significantly lower than those of the unfaithful p➔tʃi mappings following training on labial palatalization (left bars; χ²(1) = 11.86, p < 0.001 before -i; χ²(1) = 4.53, p = 0.03 across vowels). Labial palatalization is preferred to non-palatalization after training, and yet seldom produced. Judgment is not simply more lenient than production after labial palatalization training: The mapping preferred in judgment is dispreferred in production (see also Zuraw, 2000).