Competing accounts debate whether glide-vowel distinctions are phonologically possible and attested. One argument (e.g., Steriade, 1984; Kaye & Lowenstamm, 1984; Durand, 1987; Deligiorgis, 1988) is that there is no underlying distinction between vowels and glides, positing that glides are instead always phonologically derived from underlying vowels in certain environments. Levi (2004, 2008), however, provides evidence from multiple languages in which glide surface forms are not fully predictable from their surrounding environment. This unpredictability leads Levi to conclude that languages can underlyingly distinguish between glides and vowels. This study maintains the assumption (as strongly motivated by Levi, 2004) that glide-vowel distinctions are available to the human phonological faculty, and it tests whether such a distinction is present and productive in the phonological system of American English. However, a further debate remains open regarding how such distinctions should be phonologically represented. This study therefore considers competing representation accounts and compares them as candidates for representing the apparent distinction in American English.

One kind of representation account proposes that glide-vowel distinctions are attributable to a distinction in the segment’s primary articulator: A place-based representation. In an analysis of multiple languages, Levi (2004, 2008) proposes that all vowels are primarily [Dorsal], while glides’ primary articulators differ. Levi suggests that /w/ is primarily [Labial], while /j/ is primarily [Coronal], in accord with Halle et al.’s (2000) Revised Articulator Theory. As one example, Levi (2008) describes Pulaar as having both derived and underlyingly phonemic glides, with the derived glides being predictable by the surrounding environment while the phonemic ones are not. To argue how they are represented, Levi analyzes how the glides participate in a previously documented (Paradis, 1992) process of consonant gradation, alternating with more fortified counterparts. She demonstrates that the fortified versions of phonemic /j/ and /w/ have coronal and labial places of articulation ([d͡ʒ] and [b], respectively), while their derived (underlyingly vocalic) counterparts fortify to a dorsal place of articulation ([ɡ]). This representation approach is similar, though not identical, to other representations previously put forth, such as proposals that palatal [j] is both [Coronal] and [Dorsal] (e.g., Keating, 1988; Nevins & Chitoran, 2008). In terms of how such a distinction might manifest in production, we might expect tighter constriction at these more anterior places of articulation. Regarding another language, Karuk, Levi (2008) corroborates such predictions while discussing how the /w/ glide is documented (Bright, 1957) to exhibit bilabial frication. Furthermore, Keating’s (1988) conclusion that [j] is both [Coronal] and [Dorsal] comes from X-ray analysis demonstrating coronal constriction during the production of [j]. Therefore, in the analysis at hand, the primary articulation of the [j] glide would be predicted by this account to be more anterior than that of its [i] vowel counterpart. In terms of constraints on the phonological distribution, such a representation might predict this distinction to exhibit homorganicity effects and be constrained by the place of articulation of surrounding sounds.

Another kind of account, henceforth referred to as a constriction-based representation, makes use of the notion of constriction degree to distinguish glides and vowels, positing that the production of glides involves tighter constriction of the vocal tract than the production of their vowel counterparts. Padgett (2008) proposes that in systems with a glide-vowel contrast there is no difference of articulator or frontness of articulation, but only that of the feature [±vocalic]. Padgett proposes that glides, being [–vocalic], have a distinctly tighter degree of constriction than their [+vocalic] counterparts, equal along all other featural dimensions. One of the examples Padgett provides is the previously documented (Townsend & Janda, 1996) pattern of Slavic stops mutating into palatalized, affricated counterparts. This pattern is more frequent when a stop is followed by a glide than when followed by a vowel, and more frequent when a vowel is high than when it is not. Padgett argues that this scale of likelihood is attributable to the degree of constriction of the following segment: The narrower a following segment, when coupled with the release of the stop, the more likely the release is to be perceived and reanalyzed as affrication; therefore, the glide is narrower than its high vowel counterpart. This is similar to previous proposals suggesting that glides have narrower constriction targets (e.g., Straka, 1964; Maddieson & Emmorey, 1985), with arguments referring both to phonological distribution and phonetic properties such as a lower acoustic intensity of glides. Such proposals vary, however, in precise feature specification, such as employing [±consonantal] instead of [±vocalic] (e.g., Hyman, 1985; Hayes, 1989; Rosenthall, 1994). For the distinction of interest in this study, such an account would entail that the production of a lingual [j] glide has a tighter constriction reached by a higher lingual articulation than its [i] vowel counterpart. In terms of distribution, this representation might predict the factor of sonority or openness to play a role in constraining the distinction.

Another kind of account is what will be referred to as a syllabic pre-linking account. Levi, in her cross-linguistic documentation and analysis (2004), maintains that two different types of glide-vowel distinctions are typologically possible. One is the place-based representation as introduced above. The other is based on Levin’s (1985) notion of ‘pre-linking’ with respect to syllabification. In this type of system, glide and vowel counterparts are identically featured with respect to both place and constriction. Instead, identical segments in the lexical representation can be anticipatorily specified in terms of how they will be syllabified. While Levi (2004) concludes in favor of a place-based representation for the distinctions observed in some languages, she concludes that an apparent distinction in Spanish is best analyzed as a syllabic pre-linking kind of system, with some cases of vowels exceptionally specified in the lexeme’s underlying form to surface as vocalic syllable nuclei in environments where Spanish phonology more commonly dictates them to surface as their non-nuclear glide counterparts. This is in line with other previous accounts (e.g., Roca, 1997; Harris & Kaisse, 1999) suggesting that the [GV]-[VV] distinction is a result of underlyingly specified syllabification of identically featured vowel phonemes. In the case at hand, both [j] and [i] surface forms would be underlyingly /i/ and an [iV] hiatus output would be the result of the underlying /i/ having been pre-specified to surface as a syllable nucleus, therefore not being parsed into the syllable margin as might otherwise be allowed or preferred by the language’s phonotactics. Regarding production, due to this difference in syllabification, such a distinction might be predicted to manifest mainly via timing differences, with a glide being shorter than its vowel counterpart but not of a differently specified target or degree of constriction. Along these lines, Catford (1977, p. 165) argues that glides are intrinsically fast and dynamic without a ‘noticeable duration’ like their vowel counterparts (cf. Maddieson, 2008), but identical in terms of ‘articulatory stricture.’ Regarding distribution, Levi (2004) suggests that such a distinction is more idiosyncratic and marked, and that the vocalic option is underrepresented across the lexicon.

The next section will discuss where glide-vowel distinctions appear available or constrained in the American English phonology. However, these observations regarding the distribution do not strongly speak to which kind of representation might be best applicable to the case at hand, therefore motivating analysis of production and how it may speak between the competing accounts.

The [j] glide in American English can occur as a simplex word-initial onset, followed by a host of following vowels (e.g., yolk [jok], year [jiɹ], Yale [jel], young [jʌŋ]). However, we rarely encounter word-initial cases of [iV] hiatus, except a few cases in which the initial segment is stressed (e.g., eon [íɑn], Ian [íən])1; the glide-vowel distinction may therefore not be available in this environment without being confounded with stress. Following word-initial consonants, the distinction appears to be available: Pairs like fjord [fjɔɹd] + Fiona [fiónə] and dwell [dwɛl] + duet [duɛ́t] exhibit the [j]-[i] and [w]-[u] distinctions, respectively. This study therefore limits the analysis to environments with a preceding consonant ([C_V]), where the distinction between a glide and its unstressed vowel counterpart does seem to be available. Another narrowing of the scope of this analysis regards [ju]. This study focuses only on [j] when it is its own glide segment, rather than part of a diphthongal nucleus. There is a large and varied host of [CjV] items in which the following vowel ([_V]) is [u] (e.g., fume [fjum], huge [hjud͡ʒ], cute [kjut]). However, previous research has shown that /ju/ appears to pattern as a monomoraic diphthong in the English phonemic inventory (Jensen, 1993; Davis & Hammond, 1995), in which the high front vocoid behaves differently from the glide of interest here. Smith (2003) further documents that nuclear vs. onset onglides can exhibit different phonological behavior. This further supports treating [j] as distinct from the glide in the [ju] diphthong. Throughout this paper, the [j] glide of interest is that which is not a member of the [ju] diphthong unless otherwise noted.

This section discusses the apparent distribution of glide-vowel distinctions in American English, narrowing in on the [C_V] environment where a glide-vowel distinction does seem to be available. There are further constraints apparent regarding the distribution of such a distinction, which may speak to our consideration of competing phonological representations. However, it is important to note that this distinction does not appear to be robustly prevalent across the English lexicon—an aspect which (according to Levi, 2004) would lend support to applying the syllabic pre-linking representation—and is not well documented. It is also variable across words and speakers. Therefore, the reported surface forms of different words considered here are most certainly not meant to be presented as categorical, but they have been cross-checked with the reports of other linguists and the transcriptions provided by multiple online dictionary sources (e.g., Dictionary.com [dictionary.com], Merriam-Webster [merriamwebster.com], Cambridge Dictionary of American English [http://dictionary.cambridge.org/us/dictionary/english/]). While some dictionary entries acknowledge potential for variation between [jV] and [iV] pronunciations, some list only one pronunciation and, across them, a majority vote can become apparent. A final note before proceeding is that, when considering the phonological distribution of glides and vowels in this section, the [w]-[u] paradigm is also taken into account simply to show that the distributions seem similarly constrained across the two paradigms. However, as has already been made clear, the experimental analysis conducted in this study focuses on the [j]-[i] distinction. (This is largely due to complications that would arise in trying to apply acoustic phonetic analysis alone, as pursued in this study, to aptly describe the articulation: Given the labial gesture, additional ultrasound analysis [e.g., Gick, 2002; Stone, 2005; Davidson, 2006] of lingual constriction and positioning would be ideal to provide a full description of how [w] and [u] may be distinctly produced).

One apparent constraint is that of the place features of neighboring segments. First regarding the [w]-[u] paradigm, there seem to be no cases of [CwV] in which the following vowel or diphthong involves a high back vocoid (e.g., *[Cwaʊ], *[Cwu] [Davis & Hammond, 1995]). The appearance of [w] in [CwV] sequences also seems to avoid labial preceding consonants (e.g., *[fwV] [Clements & Keyser, 1983]).2 While [w] is considered labiovelar, [CwV] sequences with dorsal preceding consonants are not banned (e.g., quit [kwɪt], awkward [ɑ́kwɚd]). Regarding the [j]-[i] paradigm, there are many fewer cases of [CjV] sequences. In fact, Davis and Hammond’s (1995) paper titled, “On the status of onglides in American English,” doesn’t mention non-[ju] cases of [j] when discussing post-consonantal environments. However, some near-minimal pairs do show a distinction between [i] and [j] (e.g., Estonia [ɛstóniə] + pneumonia [nʊmónjə]). Many of these cases are variable, but they do show trends analogous to those apparent regarding [w]. No such cases are ever followed by a nucleus containing a high front vocoid such as *[Cjaɪ] or *[Cji]. Regarding place of articulation of the preceding consonant, the case of fjord [fjɔɹd] suggests that preceding labial consonants do not prohibit the glide. A more established word in English, piano, also allows for [j] in surface form [pjǽno] (while exhibiting inter-speaker variability with [piǽno]). In cases where we might expect [j] to appear following a dorsal consonant, such as the borrowing of placename Kyoto (Japanese source form [kʲoːto]), the adaptation instead appears to prefer a full [i] vowel in American English ([kióɾo]). We also do not see word-initial [CjV] sequences in which the preceding consonant is coronal. These observed homorganicity constraints could support a place-based representation, with a possible interpretation being that both restrictions against preceding dorsal and coronal consonants are due to homorganicity and that /j/ is therefore underlyingly both coronal and dorsal (Keating, 1988; Nevins & Chitoran, 2008; cf. Levi, 2008).

The sonority of the preceding segment also appears to constrain the distribution of glides. Take, for example, the loanword adaptation of French noir (source form [nwaʁ]). While [w] is allowed after other coronal consonants (e.g., dwarf [dwɔɹf]), noir is commonly adapted to [nuɑ́ɹ]. Following Steriade (1988), homorganicity constraints can play a role in the interactions of segments both within the syllable margin and between the margin and the nucleus (as observed above), while sonority constraints only play a role within the syllable margin but not between the margin and the nucleus. Therefore, the adaptation of noir banning a *[nw] onset while allowing [tw], [dw], and [sw] onsets could be attributable to the constraint against the flatter sonority cline within that complex onset. A parallel pattern is apparent regarding [j], with no clear cases of a word-initial *[mj] onset. (The fact that music invariably maintains the form [mjúzɪk] is one argument in support of the glide in [ju] pertaining to a diphthongal nucleus, suggesting that the nasal and glide are not both within the syllable margin where the constraint against a flatter sonority cline would be applicable).

Turning attention to word-medial position, it appears that both homorganicity and sonority constraints may be circumvented, with [j] appearing after [n], which is both coronal and a sonorant (e.g., Kenya [kɛ́njə], pneumonia [nʊmónjə]). This seems due to the option of licitly syllabifying the preceding consonant to the coda of the preceding syllable (e.g., [kɛ́n.jə], [nʊ.món.jə]). However, this syllabification appears to be constrained by the sonority of the preceding consonant. In the adaptation of placename Tokyo, in which a glide adaptation might be expected as a more faithful replication of the Japanese source form [toːkʲoː], the homorganicity constraint regarding the preceding consonant seems to reappear, resulting in a full vocalic adaptation ([tó.ki.o]). Following Gouskova (2004), this may be due to what would otherwise be too steep a rise in sonority across the syllable boundary (*[tók.jo]). Avoiding coda syllabification of the voiceless stop, the homorganicity constraint then applies, which disprefers the complex *[kj] onset in the *[tó.kjo] adaptation candidate and leads the [tó.ki.o] candidate to be the winner. The observation that sonority cline constraints may play a role in the distribution of this distinction could lend support to a constriction-based proposal that glides are underlyingly specified as less sonorous than their vowel counterparts.

While we can further understand the constraints on this distinction by analyzing its phonological distribution, this does not present a clear choice between the competing place and constriction/height representations proposed, as both homorganicity and sonority appear to play a role. While not speaking between these two representations, the observation of both of these effects could therefore lend support to a hybrid account, like that proposed by Nevins and Chitoran (2008), that [j] differs from [i] along both the dimensions of place/articulator ([Cor, Dors] vs. just [Dors]) and constriction ([–vocalic] vs. [+vocalic]). However, as also acknowledged in this section’s discussion, this distinction appears to be somewhat infrequent across the lexicon, as well as variable. This could lend support to treating the current case as one of lexically exceptional syllabic pre-linking (Levi, 2004). The following section will turn to discussing how each of these representations generates different predictions in the articulation and, therefore, acoustics of the [j]-[i] distinction of interest here, motivating the acoustic analysis pursued in this study.

The competing phonological representations considered above generate different predictions regarding the acoustics of the [j]-[i] glide-vowel distinction of interest in this study. There are acoustic aspects widely considered to correlate with lingual frontness, height, and constriction. There are also aspects related to timing that may play a crucial role in conveying such a distinction no matter how it is represented, though they would arguably play the only role in the syllabic pre-linking account. Therefore, analyzing the acoustics of such a distinction may speak to which representation appears more directly borne out in production, or at least rule one out.

Recall that a place-based representation suggests that /j/ is primarily [Coronal] (or at least includes a [Coronal] specification), while /i/ (like all vowels) is [Dorsal]. This predicts that a [j] production should have more fronted tongue mass than [i] if the primary articulator and/or target of constriction is anatomically more anterior. Acoustically, we can analyze F2 to examine a vocoid’s frontness: More anterior vocoids have a higher F2 than more posterior ones. This representation therefore predicts that [j] should reach a higher F2 than [i].

On the other hand, a constriction-based representation suggests that /j/ does not differ at all in place from /i/. Instead, it contends that glides have a tighter constriction than their vowel counterparts. In this case, then, [j] production should involve a tighter constriction achieved by a higher lingual articulation. Two acoustic measurements may capture this. The first is F1, which can be used to examine a vocoid’s height: Vocoids of a higher lingual articulation have a lower F1 than vocoids of a lower lingual articulation. This representation therefore predicts that [j] should reach a lower F1 than [i]. It also predicts that [j] should have a lower acoustic intensity due to its narrower constriction of the vocal tract.

There is acoustic documentation suggesting that we may find such acoustic aspects to characterize the distinction at hand. In studies of intervocalic glides (i.e., [VGV] environments), a dip in intensity between the first and second vowel is observed when an intervening glide is present, as compared to [VV] hiatus (e.g., Aguilar, 1999; Davidson & Erker, 2014). However, especially given Straka’s (1964) finding that there does not seem to be some consistent threshold across phonological contexts, this could differ in the environment of interest here ([C_V]). Additionally, in an acoustic phonetic analysis of glides and other approximants in English, Espy-Wilson (1992) finds [j] to correlate with a higher F2 and lower F1 than [i], therefore potentially supporting a combination of the place- and constriction-based representations (like that put forth by Nevins & Chitoran, 2008). However, that study does not directly examine this potential underlying distinction in controlled and balanced environments but the comparative acoustics of differently identified surface forms.

In a syllabic pre-linking account, only timing should play a role in conveying such a distinction since no difference is proposed regarding place or constriction. One way is in the duration of the entire vocalic sequence. A [jV] sequence may be shorter overall than a [iV] sequence due to the prior being one syllable instead of two. Crystal and House (1990) observe that the number of syllables within a stress group can influence its duration: More syllables means a longer duration. They also find that syllables with fewer segments tend to be shorter. And while a [iV] sequence has more syllables (two as opposed to one), those syllables each have fewer segments. However, the effect size observed by Crystal and House is greater for higher prosodic units. Therefore, based on the number of syllables (vs. number of phones per syllable), the prediction stands that a [jV] sequence’s duration will be shorter than that of a [iV] hiatus sequence.

Another timing factor that could play a role is the speed of transition. We might expect a [jV] sequence to have a faster transition than a [iV] sequence. Liberman et al. (1956) suggest that this is the case, at least on perceptual grounds. In a perceptual experiment using simulated (drawn formant) speech stimuli, they find that the speed of transition from the formant starting point to the target formant state of the following vowel influences listeners’ perceptions: Fastest leads to a [CV] percept; slowest leads to a [VV] percept; in between leads to a [GV] percept. Studies of production have also confirmed temporal aspects regarding formant transitions to distinguish glides. In a study of English diphthongs, Gay (1968) finds that the rate of transition of F2 serves as a reliable distinguisher between diphthongs.

A final timing factor to consider is the earliness of transition. That is, the distinction may not necessarily be about how fast the transition is, but how early it starts. The phonological interpretation that [j] is in the syllable margin with [C_], while [i] is further structurally separate as a member of the syllable nucleus, would suggest a tighter gestural coordination between a glide and the preceding consonant, whether directly formalized (á la Gafos, 2002) or a result of the gestural planning of the relative segmental syllabifications. While the studies above, as well as Chitoran’s (2002) acoustic analysis of Romanian diphthongs, examine transition speed, this study is intended to tease transition speed apart from transition earliness as potentially distinct characteristics. To summarize, multiple characteristics related to timing could therefore be central to distinguishing a [jV] sequence from a [iV] sequence: Duration of the entire sequence, speed of transition into [_V], or earliness of transition into [_V]. It could be a combination of these, or one might be a more consistent distinguishing factor.

It is important to note that all of the phonological accounts should predict the distinction to result in some kinds of timing differences like those presented above. No matter the featural representation, the glide will be part of the syllable margin, instead of the nucleus. Therefore, while factors related to timing may be found to convey this distinction, they do not necessarily rule out a place- or constriction-based representation. If we find only such timing characteristics to play a role, this may lend support to applying a syllabic pre-linking account and challenge the other representations proposed. However, if timing differences are found in tandem with the other predictions presented above, this would still lend more support to those associated accounts than to concluding with a pre-linking account. This is because, if anything, a pre-linking (which we could also think of as the timing- or structure-only) account would predict the reverse in terms of formants and intensity. If the glide were identically featured yet forced to the syllable margin, the faster articulation might predict a lessened amplitude of articulator movements, resulting in formant centralization due to not fully reaching the target (Gay, 1981; Browman & Goldstein, 1990; Turner et al., 1995).

To summarize the acoustic predictions generated by these competing accounts: All accounts should predict some kind of timing difference due to syllabification, with a [jV] sequence showing a shorter overall duration, an earlier transition to [_V], and/or a faster transition. The place-based representation also predicts acoustic evidence that [j] is more front than [i], and that it therefore has a higher F2. The constriction-based representation, instead, predicts that [j] has a lower acoustic intensity and/or a higher lingual articulation and therefore a lower F1. A finding of only timing differences, possibly in tandem with formant centralization, would lend stronger support to the syllabic pre-linking account.

There were 1672 utterances examined, after excluding tokens that were produced in an unexpected way (e.g., the vocoid of interest pronounced as [aɪ], a relevant neighboring segment mispronounced, stress misplaced, the sequence held out as a speech delay). Praat software (Boersma & Weenink, 2015) was used for segmentation and analysis. The entire [jV]/[iV]-expectant vocalic sequence was segmented. The beginning (henceforth ‘vocalic onset’), was identified as the onset of F1 after an obstruent or re-strengthening of formants after the release of a preceding nasal. The end (henceforth ‘vocalic offset’) was identified as the severe reduction in amplitude or complexity of the formants attributable to the following consonant. All acoustic measurements were performed over this entire vocalic sequence.

The following reviews what this distinction might look like acoustically. In line with a place-based representation, we would expect that [j] has more anterior raising of tongue mass than [i], and therefore a higher F2. In line with a constriction-based representation, we would expect that [j] has a higher lingual articulation and tighter constriction than [i], and therefore a lower F1 and lower acoustic intensity. As predicted by all accounts (now including that of syllabic pre-linking), timing may also play a role, with a [jV] sequence being shorter overall, having an earlier transition, and/or having a faster transition than a [iV] sequence.

Figure 1 shows spectrograms of utterances by the same speaker of Estonia [CiV] and pneumonia [CjV] appearing to exhibit the distinction. Inspection confirms some of the predictions above. The [jV] sequence is of a shorter duration overall than that of [iV]. In terms of the F2 trajectory, the [iV] sequence appears to take longer to reach its maximum before transitioning downward toward the following vowel, suggesting that the [jV] transition starts earlier. However, the F2 max is greater for [iV] than for [jV], suggesting that [j] is less front than [i]—the opposite of that predicted by the place-based representation. The intensity tracker also shows a greater jump in the [jV] case (+6.1 dB) than the [iV] case (+3.5dB), suggesting that [j] has a lower intensity relative to [_V] than [i] does, and [jV] has a lower F1 min, suggesting a higher lingual articulation. Other than that of F2 max, these observations are all in line with the acoustic phonetic predictions discussed above.

Table 3 summarizes the measurements, predictions, and how each relates to the competing representation accounts. All measurements were performed across the entire segmented vocalic sequence using a Praat script. The maximum value of F2 was identified and recorded (F2 max) to examine frontness: A higher value for [j] would mean that it is more front than [i], therefore supporting a place-based representation. The minimum value of F1 was identified and recorded (F1 min) to examine height of lingual articulation: A lower value for [j] would mean that it is of a higher lingual articulation than [i], therefore supporting a constriction-based representation. The minimum intensity value was recorded and subtracted from the maximum intensity value (intensity range): A greater intensity range for [jV] would mean that [j] has a lower intensity relative to [_V], therefore supporting a constriction-based representation. The amount of time between the voicing onset and the timepoint at which F2 max occurred was also recorded (F2 max time) to examine the transition starting point (following Chitoran, 2002 and Ren, 1986), predicting a [jV] sequence’s transition to begin earlier. (See Section 4.3 for further discussion regarding the choice to treat this measurement of earliness as absolute—milliseconds from voicing onset—rather than relative—such as percentage of the entire vocalic sequence’s duration). The timepoint and value of the F2 minimum were recorded and used to calculate the slope of F2’s transition between that point and F2 max (F2 slope), predicting a [jV] sequence to have a greater F2 slope and therefore a faster transition (as suggested by Liberman et al., 1956). Finally, the overall duration was measured between vocalic onset and offset, predicting a [jV] sequence to have an overall shorter duration than a [iV] sequence.

Of course, one possibility is that there is no significant difference along any measurement, which would not support the hypothesis that a distinction was elicited (at least as detectable by the measurements taken here). An observation in the opposite direction of one of the predictions above would motivate ruling out the associated account. For example, an observation that [j] has a lower F2 max would suggest that a place-based approach is not a good fit for representing the distinction at hand. An observation that any predictions from the first two sets are borne out would lend support to the associated account(s). For example, an observation that [j] has a higher F2 max would support applying a place-based representation. However, that observation in tandem with a lower F1 min or wider intensity range could be interpreted as inconclusive between place- and constriction-based accounts, or as support for a hybrid approach that both features are part of this distinction’s specification (e.g., Nevins & Chitoran, 2008). Furthermore, as discussed above (Section 2.3), if we observe any predictions from the first two sets in tandem with any from the final set of timing-related predictions, this would still lend more support to those accounts than to a syllabic pre-linking account, since a difference in syllabification and therefore timing is predicted by all accounts. Strongest support for a syllabic pre-linking account would come from observing only timing-related differences.

A linear mixed-effects model was performed for each of the acoustic measurements using the lme() function from the nlme package (Pinheiro et al., 2017) for the R statistical programming environment (R Core Team, 2015). This tested expected pronunciation as the independent variable for its effect on each acoustic measurement as the dependent variable. To capture the paired nature of the experimental design, a random effect (intercept and slope) was included for each combination of speaker and near-minimal pair. For example, anatomical differences might lead formants to have a higher average for one speaker than another, and that could also affect the magnitude of the difference in any formant used by that speaker to convey the distinction. Or, one speaker might not exhibit the distinction for one word pair, though they exhibit it for another. Or, timing-related factors might be used differently for one word pair than another, such as the distinction being realized differently between the Kenya + millennia pair and the California + hernia pair due to differing syllable counts, seeing as entire word length can affect the duration of syllables within the word (Lindblom, 1968).

The results of this analysis are presented in Table 4. The first three columns are descriptive statistics. ‘Percent [i] > [j]’ describes what proportion of near-minimal utterance pairs exhibit a difference in the [i] > [j] direction; the farther this number is from 50% means an acoustic difference is less chance-like in its patterning and therefore more consistent in conveying this distinction. The means of both categories are also provided. The final two columns are results of the statistical models applied. The ‘Coefficient: [j]-expectant’ is how much and in what direction the model predicts an acoustic measure to differ from the [i]-expectant prediction (the intercept) when the utterance is of a [j]-expectant stimulus.

The expected glide-vowel distinction across the near-minimal word pairs appears borne out in the data along multiple acoustic dimensions. The [j]-expectant counterparts have significantly earlier transitions into the following vowel, as represented by the earliness of F2 max, and significantly shorter durations of the entire vocalic sequence. They also have significantly wider intensity ranges, suggesting that [j] has a lower intensity relative to that of the following vowel. A difference in frontness, as represented by F2 max, is also significant but in the opposite direction than that predicted by a place-based representation: [j] has a significantly lower F2 max, and thus a less anterior constriction than [i]. And the measurement of F2 slope suggests that [j] has a significantly faster transition into the following vowel. F1 min shows no significant effect. Figure 2 provides visualizations of each measurement’s results, grouped by expected pronunciation.

These results suggest that a [j]-[i] distinction is present between near-minimal pre-existing word pairs and that timing may be the most reliable distinguisher between [j] and [i]: [jV] sequences are shorter than [iV] sequences, seemingly brought about by an earlier and faster transition into [_V]. The results also challenge applying a place-based representation, with a difference in frontness found to be significant but in the reverse direction of that predicted by this representation: [j] is less anterior than [i]. This could be a by-product of timing, as discussed earlier (Section 2.3): [j] being faster than [i] could result in more reduction and formant centralization, therefore keeping [j] from reaching its front target (however anterior that target may be) and in this case resulting in a significantly less anterior realization than that of [i]. Results speak in support of applying a constriction-based representation. The intensity range effect suggests that [j] has a lower intensity, relative to that of the following vowel. Furthermore, the lack of a significant reverse effect for F1 min like that observed for F2 max could suggest that the target is actually a higher articulation than [i] but production is reduced due to the faster articulation, though not to a realization lower than (only insignificantly different from) that of [i]. In summary, these results challenge applying a place-based representation and support applying a constriction-based representation, at least regarding the production of pre-existing near-minimal word pairs in American English.

This section extends the same analysis to the nonce stimulus data, with analogous linear mixed-effects models of each measurement across the condition of stimulus orthography, where a <i> orthography expects a [i] output and a <y> orthography expects a [j] output. Again, a random effect was specified for each combination of speaker and near-minimal pair. The results are presented in Table 5, with the format exactly like that of Table 4 regarding the pre-existing lexical item results.

Again, the expected glide-vowel distinction across the near-minimal nonce stimulus pairs appears borne out in the data along multiple acoustic dimensions. The [j]-expectant counterparts have significantly earlier transitions into the following vowel and significantly shorter durations of the entire vocalic sequence. There is again a significant effect on the intensity range, however this is in the reverse direction ([i]-expectant stimulus utterances show a greater intensity range across the vocalic sequence than [j]-expectant stimulus utterances). It’s possible that this is a task effect. Recall that stress placement was explicitly marked in the nonce stimuli and used as a distractor variable during the experiment. Subjects may have been hyperarticulating stress by using a wider than normal intensity range to distinguish stressed syllables from unstressed syllables. The hyper-differentiation of intensity between syllables may be overriding any observably lower intensity of [j]. However, this potential for reversal does suggest that intensity may not be the most reliable characteristic of this distinction. The remaining measurements pattern in parallel with the results of the pre-existing lexical items discussed above. F2 max again patterns counter to what would be predicted by a place-based representation, with [j] having a lower F2 max (this time approaching, while not reaching, significance) and therefore a less anterior articulation. Figure 3 provides visualizations of each measurement’s results, grouped by expected pronunciation (in this case, stimulus orthography).

These results suggest that the [j]-[i] distinction observed between pre-existing near-minimally paired lexical items (Section 4.1) is also productively extended to new words, as elicited via the <y> vs. <i> orthographic distinction, and across a wider variety of surrounding environments. They further suggest that transition earliness and overall vocalic sequence duration are the more consistent acoustic dimensions that convey this distinction ([jV] sequences are shorter than [iV] sequences, with the transition into [_V] coming earlier after [j] than after [i]). The nonce stimulus results continue to challenge applying a place-based representation to this case, with [j] again found to have a lower F2 max and therefore a less anterior articulation—the reverse of that predicted by this representation. However, these results speak less strongly in favor of a constriction-based representation, with [j] now appearing to have a greater intensity with respect to that of the following vowel. How to conclude or proceed based on these observations will be further discussed below (Section 5).

While the central pursuit of the nonce stimulus part of this study is to examine what acoustic characteristics consistently convey this distinction across a more diversified array of surrounding environments, the data may also speak to how those environmental factors constrain the distinction’s availability. Table 6 reports measurements of what appears to be the most consistent characteristic, transition earliness as measured by F2 max time, across the different environmental conditions of word position and place of articulation of the preceding consonant that were manipulated in the nonce stimuli. Though linear regression modeling of each environmental condition’s effect (testing for a significant interaction between condition and orthography as a predictor of F2 max time) finds no effect to be significant, the distinction’s availability does appear to pattern in some expected ways by being realized more consistently in certain conditions. It is apparently more available when the preceding consonant is in medial position rather than initial position. This, as previously discussed above (Section 2.2), could be due to consonants that would otherwise disprefer sharing a complex onset with the glide being more readily parsed as the coda of the preceding syllable when the consonant is not word-initial. The distinction is also apparently more available when the preceding consonant is coronal or labial and less available when the preceding consonant is dorsal (the strongest factor appearing to limit the distinction’s availability). This suggests a homorganicity constraint banning [Cj] sequences when the preceding consonant is dorsal (to be discussed further still in Section 5).

Given that transition earliness appears to be the most consistent differentiating characteristic of this distinction, it is briefly given some more nuanced attention here. In the above analyses, transition earliness is treated as an absolute measurement: How many milliseconds after the onset of a [jV]/[iV] sequence is the maximum F2 reached before its descending transition into the following vowel begins? However, we know that the duration of a segment can be influenced by segment-extrinsic factors like speech rate (Goldman-Eisler, 1968; Grosjean & Lane, 1976; Gay, 1978; Hirata, 2004), whether a segment appears in a stressed syllable (Lindblom, 1963; Klatt, 1975), and the crowding of its prosodic environment, such as the number of syllables in a stress group (Crystal & House, 1990). This consideration might, therefore, motivate examining transition earliness as a relative, proportional measurement rather than an absolute measurement: How far percentage-wise into a [jV]/[iV] sequence (no matter its entire duration) does the transition to [_V] begin? A [jV] sequence may show an average F2 max occurrence time of 20ms and an average total duration of 185ms, but it might be hypothesized to come later than 20ms after the onset in a longer [jV] sequence of, say, 200ms total. Therefore, a relativized measurement may capture the distinction better across a diverse array of environments by accounting for this potential variation.

On the other hand, effects on segmental duration are not entirely absolute or consistent. Studies examining the effects of speech rate have observed that pauses (Goldman-Eisler, 1968) and vowels (Kozchevnikov & Chistovich, 1965; Gay, 1978) are the main loci of duration changes across different speech rates. Furthermore, Klatt (1973) argues that segments may have intrinsic absolute durations that become apparent when considering segment-extrinsic influences. When testing a model of segment duration incorporating multiple factors that have been found to influence it, Klatt observes that vowel categories seem to have respective floors of compressibility at which point the model’s predictions of shorter durations fail. Absolute duration may therefore play an important role in the characterization of a glide as well. Like Klatt observes regarding vowels, there could be a floor of compressibility for glides, albeit shorter. A duration shorter than that floor might, instead, resemble the very fast formant transition after a consonantal constriction. This is supported at least on perceptual grounds by Ohala’s (1978) analysis that a change in Southern Bantu in which palatalized labial stops /pʲ/ changed to coronal stops /t/ is due to the reanalysis of [ʲ] as a formant transition. (The coronal, as opposed to dorsal end result may be explained by the labial [p]: The high starting point of the F2 transition that would result from palatalization, and therefore resemble a dorsal transition, could have been mitigated by the low starting point after the labial constriction and therefore result in something in between the two). We might also imagine a ceiling of expandability at which point a glide is no longer glide-like but vowel-like, no matter how long surrounding segments may be. This double-sided bounding of the duration of a glide is also at least perceptually supported by Liberman et al.’s (1956) finding that when increasing the speed of formant transition from a high F2 starting point, listeners’ percepts change from [iV] to [jV] and then to [ɡV].

The data below provide a fuller description of transition earliness. In Table 7, the timepoint at which F2 max occurs is represented both in Relative (percentage of entire vocalic sequence duration) and Absolute (milliseconds after vocalic onset) terms. Figure 4 provides a series of Smoothing Spline ANOVA plots (Gu, 2002) of the F2 contours of two pre-existing lexical item pairs: One pair of those most similar in the entire form (Estonia + pneumonia), and another pair less so (millennia + Kenya). These plots are based off 50 equidistant measurements of F2 across the entire vocalic sequence, fitting curves to the datasets being compared and providing Bayesian confidence intervals to determine areas of significant difference between the formant contours.3 The Relative versions show the F2 contour in terms proportional to the duration of the entire vocalic sequence, where the x-axis is the ordinal number for each of the 50 equidistant measurements (‘timepoint’). For the Absolute versions, the x-axis is the conversion of these measurement points to their absolute duration, the number of milliseconds after vocalic sequence onset (‘raw timepoint’).

These results demonstrate that both the absolute and relative approaches to the measurement of transition earliness significantly reveal the distinction. However, they also suggest that an absolute approach to measuring transition earliness may be more consistent at capturing it. The results in Table 7 suggest that looking at how many milliseconds after the vocalic sequence’s onset the F2 max is reached is a more consistent identifier of this distinction than looking at how far proportionally into the entire vocalic sequence’s duration it’s reached. Additionally, a more holistic analysis of the F2 contours in Figure 4 suggests that the contours are not always identified as significantly distinct when relativized to the entire sequence’s duration, rather than anchored to real time. As discussed above, the relative approach is meant to account for other effects, such as a less exact environmental pairing. However, the absolute approach does seem to still capture the distinction across cases and fares better at doing so in a case of more similar environmental pairing.

Furthermore, when examining the Absolute plots, it is apparent that the confidence intervals become wider toward the end of the contour (the right side). This is due to variation in the duration of the entire sequence: When some utterances have shorter durations, there become fewer measurement points that can be referred to in the calculation of the confidence interval. So the entire sequence duration seems to vary, but the [j]-[i] distinction is still apparent when examined in absolute terms. The combination of these observations suggests that this variation of the entire sequence’s duration may be more attributable to varying duration of the following vowel (corroborating findings mentioned above [e.g., Kozchevnikov & Chistovich, 1965; Gay, 1978]). This somewhat orthogonal behavior lends support to the notion that, in [jV] and [iV] sequences, the prior and latter segments are truly separate concatenated segments rather than parts of a single complex unit.