1. Introduction
Within the tradition of Hispanic linguistics, the quantity of research on heritage speakers (HSs) of Spanish has expanded over the past few decades, as can be seen from the increase in edited volumes [
1,
2,
3,
4,
5,
6,
7] and state-of-the-art review articles [
8,
9,
10,
11,
12,
13,
14,
15] on the subject. Although the quantity of research on this population has increased, Rao and Ronquest point out that the majority of the research has focused on morphosyntax and pedagogy, while phonetics and phonology have received less attention in the literature [
14]. Therefore, the present study seeks to expand our knowledge of Spanish HS phonetics and phonology by investigating the role that code-switching and lexical stress play on Spanish HS vowel production, particularly if simultaneous activation of English and Spanish reduces the vowel quality and duration of Spanish vowels. While previous studies have found a significant effect of lexical stress on Spanish HS vowel quality and duration [
16], code-switching has not been examined within this particular area.
One commonly used definition of a heritage speaker is an individual “who is raised in a home where a non-English language is spoken. The student may speak or merely understand the heritage language and be, to some degree, bilingual in English and the heritage language” [
17] (p. 1). An individual within this population is characterized by having early exposure to the heritage language (HL), which, in the case of the present study, is Spanish. However, research has shown that Spanish HSs typically only receive HL input in familiar contexts, meaning that they often receive little formal education in the HL [
18,
19,
20]; consequently, many Spanish HSs are dominant in Spanish at a young age, but shift to English-language dominance as they get older, due to their increased use of English once they enter the education system [
20,
21]. This exposure to Spanish at home and lack of formal education in the HL typically results in advanced oral and comprehension skills, and variable abilities in formal and written registers. However, this is not the case for proficiency in English, as Spanish HSs tend to use English in academic, social, and workplace settings, leading to more advanced and consistent skills in the majority language [
18].
One major line of research in HL phonology has been to investigate whether or not HSs have a similar phonological system to their monolingual counterparts and/or second language (L2) learners, with respect to production.
1 For example, early studies on Spanish HS [
25,
26,
27] and Korean HS [
28] found differences between monolingual speakers, HSs, and L2 learners in their phonetic productions; furthermore, these studies found differences within the HS population, in that childhood speakers outperformed childhood overhearers.
2 Hrycyna et al. [
29] also showed differences between two HL populations (i.e., Russian and Ukrainian) living in Toronto and their monolingual counterparts by showing that these participants had longer voice onset time (VOT) values, presumably due to contact with English, which has long-lag VOT values for its voiceless stops. Additionally, Godson demonstrated how English affected the vocalic system of Western Armenian HSs [
30]. Finally, Saadah’s investigation of short and long vowels in monolingual Arabic speakers, Arabic HSs, and L2 learners found that the HSs presented patterns more similar to L2 learners with the vowel /u:/, and while they differed from both monolingual Arabic speakers and L2 learners with /a, a:, u/ [
31].
Although several studies have found differences between HSs and monolingual speakers, as well as with L2 learners, other studies have found that HSs may not be different from monolingual speakers. For example, the Italian HS group in Hrycyna et al. did not produce long-lag VOT values, which led the authors to speculate that the cohesiveness of the heritage communities and opportunities to speak the HL outside of the home may account for the variation in VOT values across the three languages [
29]. Additionally, Saadah found that the Arabic HSs were similar to monolingual Arabic speakers with respect to the high fronted vowels /i, i:/ [
31]. Finally, Chang et al.’s study of monolingual Mandarin and Mandarin HSs also found that their HS group maintained phonemic contrasts in Mandarin, and also differentiated between several similar English and Mandarin sounds (i.e., back vowels, stops, and fricatives) [
32]. Therefore, while some studies show that HSs may be different from their monolingual counterparts [
25,
26,
27,
28,
29,
31], other studies have shown that HSs are able to acquire and maintain the phonological systems of both of their languages [
29,
31,
32].
With respect to the phonological segment under investigation in the present study, i.e., Spanish vowels, Willis first noted that Southwest HS vowels might differ from the monolingual norms [
33], given that he found fronted productions of /a/, lowered productions of /o/, and both fronted and lowered productions of /u/, when compared to monolingual values from Quilis and Esgueva [
34]. More recently, Ronquest examined the role that lexical stress plays in the vowel quality and duration of vowels in the Spanish of HSs from Chicago [
16]. The results of the study demonstrated that all the vowels, except /a/, exhibited significant centralization of the vowel space when in atonic position; moreover, atonic vowels were significantly shorter in duration than tonic vowels. Both of these results suggest that Spanish HS atonic vowels might involve a higher degree of reduction than those of monolingual Spanish speakers [
34,
35]. Additionally, Alvord and Rogers also found centralization of all vowels, except /u/, for all their Cuban participants residing in Miami [
36], which ranged from first-generation immigrants to third-generation immigrants according to Silva-Corvalán’s [
37] categorization.
3 The authors argue that, despite observing movement towards the center of the vowel space, this was not due to English influence, given that none of the participants, with the exception of one, produced any full schwas in unstressed position.
While these studies focused on Spanish HSs’ productions in Spanish compared to monolingual Spanish speakers, i.e., a between-subjects design, it is also possible to examine participants’ language productions in two distinct situations, i.e., a within-subjects design. One framework to investigate the latter is Grosjean’s [
38] bilingual language modes framework. This framework argues that there are two possible types of influence from one language on the other:
transfer (i.e., “permanent, or relatively permanent, traces of one language on the other” (p. 13)) and
interference (i.e., “ephemeral intrusions of the other language” (p. 13)). Both of these types of influence can be observed in
monolingual mode (i.e., “[when bilinguals] are interacting only with (or listening only to) monolinguals of one—or the other—of the languages they know (p.12)”) or
bilingual mode (i.e., “[when bilinguals] are communicating with (or listening to) bilinguals who share their two (or more) languages and with whom code-switching and borrowing may take place” (p. 12)). Although Grosjean states that differentiating between these two types of influence will be difficult [
38], given that they are similar to each other and can be found in both monolingual and bilingual mode, Simonet argues that interference, or what he calls “transient interference”, should be more common in bilingual mode than in monolingual mode, since both languages are activated in bilingual mode [
39]. As noted by Simonet, one way to induce bilingual mode in speech production is to have participants code-switch [
39].
With respect to bilingual mode and phonetics, there are studies that have investigated the effects of Spanish–English code-switching on Spanish phonetics. For example, Bullock and Toribio [
40] examined the VOT of English and Spanish voiceless stops with eight early Spanish–English bilinguals, ten L1 Spanish bilinguals, and fifteen L1 English bilinguals. The results demonstrated that, despite maintaining separate phonological systems, the early bilinguals’ VOT values exhibited convergence in the direction of the opposite language; this is to say, when code-switching from Spanish to English, the early bilinguals had shorter English VOT values, while when code-switching from English to Spanish these participants had longer Spanish VOT values. While Bullock and Toribio found effects of code-switching on the voiceless stops after the code-switch [
40], Balukas and Koops found an anticipatory effect when the bilinguals switched from Spanish to English [
41]; their results showed reduced VOT values in the English tokens that were closer to the switch site, but they did not find the same effects for Spanish tokens. Piccinini and Arvaniti also found differences in VOT values between code-switching and monolingual sessions [
42]. They found that the voiceless stops, both in English and in Spanish, in code-switching utterances had shorter VOT values before and after the switch than voiceless stops in monolingual English and in monolingual Spanish utterances. Despite the differences in these studies, especially regarding the placement of the token with respect to the code-switch, they highlight the possibility that code-switching can significantly affect the phonetic production of bilinguals.
Moving beyond segmental phonology, Olson examined the effect of code-switching on suprasegmental features, specifically on pitch height and on vowel duration [
43]. The participants read aloud three different types of stimuli, one all in English, one all in Spanish, and one that code-switched from Spanish to English. Olson’s study revealed a significant difference in pitch height between the two monolingual sessions and the code-switching session, in that the code-switching session had higher pitch heights than both monolingual sessions [
43]. For vowel duration, Olson examined the duration of English vowels in stressed position in the code-switching stimuli and compared them to vowels in both monolingual sessions. The results showed that vowels in the code-switching session were significantly longer than vowels produced in both monolingual sessions. Furthermore, a comparison of the code-switching vowels to the English-only session demonstrated that vowels in the code-switching session were on average 18% longer than vowels in the English-only session. Olson’s study provides further evidence that activation of both languages in a single utterance not only affects phonetic production at the segmental level, but also at the suprasegmental level [
43].
As can be seen from previous studies on HL phonology and the effects code-switching, HS research has followed two data collection methods: assessing HS speakers while only one of their languages (i.e., their HL) is activated [
16,
25,
26,
27,
28,
29,
30,
31,
36], or testing them while both of their languages are activated via code-switching [
40,
41,
42,
43]. As Simonet demonstrated, inducing a bilingual mode may cause transient interference of one language on the other when the productions from bilingual mode are compared to productions from monolingual mode [
39]. Following this line of thought, the present study is interested in examining if there are transient effects of English, which will be activated via code-switching, on Spanish vowels that follow a code-switch within a sample of Midwestern U.S. heritage speakers of Spanish. We define potential transient effects of English in terms of changes in vowel quality and duration, i.e., vowel reduction; our study differs from previous research on Spanish HS vowels [
16,
33,
36] in that those studies only examined monolingual Spanish vowels, while the present study compares Spanish vowels produced in monolingual mode to Spanish vowels produced in a Spanish–English code-switching context (i.e., bilingual mode). Furthermore, we wish to explore the possibility that transient effects of English will be the strongest right after a code-switch, following previous findings for VOT [
41,
42]. In order to answer these questions, our study was guided by four research questions:
Is there an effect of code-switching and lexical stress on the vowel quality of heritage speakers of Spanish?
Is there an effect of code-switching and lexical stress on the vowel duration of heritage speakers of Spanish?
Is there an effect of distance from the code-switching site on the vowel quality of heritage speakers of Spanish?
Is there an effect of distance from the code-switching site on the vowel duration of heritage speakers of Spanish?
Following previous research [
16], we hypothesize that lexically unstressed vowels will differ in both vowel quality and duration from their lexically stressed counterparts. Specifically unstressed vowels will be shorter in duration and be more centralized via changes in F1 and/or F2. With respect to the effect of code-switching, we predict that the introduction of English via code-switching will produce differences in Spanish vowels after a code-switch, in that they will be shorter in duration and more centralized than Spanish vowels produced in a monolingual Spanish mode; this is based on previous research that has shown that the introduction of English makes Spanish productions more English-like than monolingual Spanish phonetic productions [
40,
42]. Finally, we hypothesize that Spanish vowels closer to the code-switch site will exhibit more effects from English than vowels that are further away from the code-switching site, in light of the results of previous research [
41,
42]. Overall, we predict that our results will show that Spanish HS vowels are different from what has been reported for Spanish monolinguals [
34,
35], and will also support previous work on HL phonology [
25,
26,
27,
28,
29,
31] and research on transient phonetic interference in bilingual mode [
39].
3. Results
The following section is divided according to the results of the linear mixed effects models for normalized F1/F2 values and vowel duration (
Section 3.1), and of the linear mixed effects models for the code-switching subset of the data to examine the potential effect of distance from code-switching site and F1/F2 normalized values and vowel duration (
Section 3.2).
3.1. Normalized F1/F2 Values and Vowel Duration
To begin this section, the F1 normalized results revealed that there was a main effect for vowel phoneme,
F(4, 3584) = 292.11,
p < 0.001, lexical stress,
F(1, 3587) = 31.54,
p < 0.001, and language session,
F(1, 3587) = 5.37,
p = 0.02, but not for DELE,
F(1, 3587) = 0.58,
p = 0.45. There were significant two-way interactions between vowel and lexical stress,
F(4, 3584) = 51.68,
p < 0.001, and between vowel and language session,
F(4, 3584) = 6.20,
p < 0.001. However, there was not a significant three-way interaction between vowel phoneme, lexical stress, and language session,
F(1, 3583) = 0.70,
p = 0.62.
Table 2 presents the mean values for the significant interactions, as well as the Cohen’s
d effect size when the post-hoc analysis revealed significant pairwise differences between the mean values, while the estimates of the fixed effects from the linear mixed effects can be found in
Table 3.
The results from
Table 2 and
Table 3 show that for the interaction between vowel and lexical stress there were significant differences in the normalized F1 values for /a/, /e/, and /o/, in that vowels in lexically stressed syllables had higher F1 values (i.e., lower in the vowel space) than their lexically unstressed counterparts. With respect to the interaction between vowel and language session, the /a/ vowels in the monolingual session had statistically significantly higher F1 values than the /a/ vowels in the code-switching session, while the monolingual /i/ and /u/ vowels had statistically significantly lower F1 values (i.e., higher in the vowel space) than the /i/ and /u/ vowels in the code-switching session.
For the normalized F2 values, there was a main effect for vowel phoneme, F(4, 3584) = 264.33, p < 0.001, but not for lexical stress, F(1, 3587) = 2.98, p = 0.08, language session, F(1, 3587) = 0.68, p = 0.41, or DELE, F(1, 3587) = 0.39, p = 0.53. There were significant two-way interactions between vowel and lexical stress, F(4, 3584) = 6.30, p < 0.001, and between vowel and language session, F(4, 3584) = 43.02, p < 0.001. However, there was not a significant three-way interaction between vowel phoneme, lexical stress, and language session, F(1, 3583) = 0.58, p = 0.72.
The results from
Table 4 and
Table 5 indicate that, for the interaction between vowel and lexical stress, there were statistically significant differences in the normalized F2 values for /e/, /i/, /o/ and /u/, but that the direction of the differences was distinct: stressed /e/ and /i/ vowels had higher normalized F2 values (i.e., more fronted) than unstressed /e/ and /i/ tokens, while stressed /o/ and /u/ vowels had lower normalized F2 values (i.e., more back) than unstressed /o/ and /u/ tokens. With respect to language session, monolingual /e/ and /i/ had higher normalized F2 values than their respective vowels in the code-switching session, while monolingual /o/ and /u/ had lower normalized F2 values than their code-switching counterparts.
To visually summarize the results in a meaningful way,
Figure 2 presents a graphic representation of the differences between Spanish vowels in the monolingual (represented by circles) and code-switching (represented by triangles) sessions. Furthermore, each vowel is represented by its own color: blue (/a/), yellow (/e/), red (/i/), purple (/o/), and green (/u/). Normalized F1 values (i.e., vowel height) are found on the
y-axis and the normalized F2 values (i.e., front/backness) are on the
x-axis. Solid black lines connect the vowels to form the vocalic triangle.
The general trend that emerges from
Figure 2 is that the monolingual session vowels occupy the outer space of the vowel chart, while the vowels in the code-switching session occupy the inner space. This is to say that although there were only statistically significant differences between F1 and F2 values and the type of session for two of the vowels (i.e., the high vowels /i/ and /u/), the other vowels had differences in either the F1 (i.e., /a/) or F2 values (i.e., the mid vowels /e/ and /o/) that moved the mean values of code-switching vowels to the inner space of the vowel chart.
A visual representation of the effect of lexical stress on normalized F1/F2 values is provided in
Figure 3. In this figure, vowel tokens in lexically stressed syllables are represented by circles and vowel tokens in lexically unstressed syllables are represented by triangles. As with
Figure 2, each vowel in
Figure 3 is represented by its own color: blue (/a/), yellow, (/e/), red (/i/), purple (/o/), and green (/u/). Normalized F1 values (i.e., vowel height) are found on the
y-axis, while the normalized F2 values (i.e., front/backness) are on the
x-axis; there is also a solid black line connecting the vowels to form the vocalic triangle.
The general trend that emerges from
Figure 3 is that vowel tokens in lexically stressed tokens are found in the outer space of the vowel chart, while vowel tokens in lexically unstressed syllables are found in the inner part of the vowel space. Although /o/ was the only vowel that showed statistically significant differences in F1 and F2 values between stressed and unstressed position, the other vowels did show movement to the inner vowel chart space either through statistically significant differences in F1 (i.e., /a/ and /e/) or F2 (i.e., /i/ and /u/).
With regard to the last dependent variable, vowel duration, given that its distribution was not normal (skewness = 1.48, kurtosis = 4.51), the raw values were submitted to log transformation to create a normal distribution (skewness = −0.40, kurtosis = 0.63). For the log values of vowel duration there was a main effect for vowel phoneme, F(4, 3584) = 77.93, p < 0.001, and lexical stress, F(1, 3587) = 135.22, p < 0.001, but neither for language session, F(1, 3587) = 0.71, p = 0.40, nor for DELE, F(1, 3587) = 3.00, p = 0.12. There was a significant two-way interaction between vowel and lexical stress, F(4, 3584) = 3.02, p = 0.02, but there were no significant interactions between vowel and language session, F(4, 3584) = 1.98, p = 0.10, and between vowel phoneme, lexical stress, and language session, F(1, 3583) = 1.74, p = 0.12.
To conclude this sub-section, the results from the linear mixed effects model in
Table 6 and
Table 7 show that lexical stress, and not language session, affected the five Spanish vowels: vowels in unstressed position were shorter in duration than vowels in stressed position. There was no statistically significant main effect for language session.
3.2. Distance from Code-Switching Site
For the code-switching subset of the data, the F1 normalized results revealed that there was a main effect for vowel phoneme, F(4, 1491) = 9.73, p < 0.001, lexical stress, F(1, 1494) = 7.58, p < 0.001, but not for DELE, F(1, 1494) = 1.20, p = 0.30, or distance from the code-switching site, F(1, 1494) = 0.51, p = 0.48. Additionally, there were no significant two-way interactions between vowel and lexical stress, F(4, 1491) = 1.99, p = 0.10, or between vowel and distance from the code-switching site, F(1, 1494) = 0.99, p = 0.41.
With respect to the normalized F2 results, the linear mixed model indicated that there was a main effect for vowel phoneme, F(4, 1491) = 5.51, p < 0.001, but not for lexical stress, F(1, 1494) = 1.29, p = 0.26, DELE, F(1, 1494) = 0.45, p = 0.50, or distance from the code-switching site, F(1, 1494) = 0.76, p = 0.38. There were no significant two-way interactions between vowel and lexical stress, F(4, 1491) = 1.48, p = 0.21, or between vowel and distance from the code-switching site, F(1, 1494) = 2.05, p = 0.09.
Finally, the results for the log values of vowel duration show that there was a main effect for vowel phoneme, F(4, 1491) = 16.04, p < 0.001, and for lexical stress, F(1, 1494) = 54.77, p < 0.001, but not for DELE, F(1, 1494) = 2.23, p = 0.17, or distance from the code-switching site, F(1, 1494) = 2.57, p = 0.11. While there was a significant two-way interaction between vowel and lexical stress, F(4, 1491) = 4.17, p = 0.002, there was not one between vowel and distance from the code-switching site, F(1, 1494) = 0.69, p = 0.60.
4. Discussion
The present study set out to investigate the effects of code-switching and lexical stress on the vocalic production of 11 Midwest Spanish HSs, in addition to exploring the possible effect of distance from the code-switching site on these phonetic productions. We examined these questions through an experimental design that asked participants to read aloud children’s stories that either contained English−Spanish code-switches (i.e., the code-switching session) or were only in Spanish (i.e., the monolingual session). These phonetic productions were then analyzed for vowel quality (i.e., normalized F1 and F2 values) and duration in order to quantify the extent of vocalic reduction.
The first research question asked, “is there an effect of code-switching and lexical stress on the vowel quality of heritage speakers of Spanish?” The results from various linear mixed effects models showed there were significant differences between the vowels in the code-switching and monolingual sessions with the normalized F1 (i.e., for /a/, /i/ and /u/) and normalized F2 (i.e., /e/, /i/, /o/ and /u/) values. These differences between the monolingual and code-switching session were in the hypothesized direction, in that the vowels after a code-switch from English into Spanish were more centralized than their monolingual counterparts, as was visually shown in
Figure 2; this is to say that even though there were not significant differences between both normalized F1 and F2 for all the vowels, there was at least one significant difference in either F1 or F2 that moved the vowels to the inner space of the vowel chart. In other words, the monolingual vowels all occupy a more outer space in the vowel chart, while the code-switching vowels occupy a more centralized space. Furthermore, it is also worth highlighting the fact that there is a large distance between all the monolingual vowels, while this distance appears to be reduced with the code-switching vowels.
The finding for the effect of code-switching on Spanish HS vowel production is consistent with previous research on Spanish−English code-switching, in which code-switching has been shown to affect Spanish voiceless stops [
41,
42]. In this pair of studies, the conflict site [
59] between English and Spanish had to deal with differences in VOT, as English is traditionally classified as a language with long-lag VOT (i.e., more than 30 ms), while Spanish is described as a short-lag VOT (i.e., between 0–30 ms) language [
60]. In both Bullock and Toribio [
40] and Piccinini and Arvaniti [
42], the introduction of English via code-switching lengthened the VOT of Spanish voiceless stops. In the case of the present study, the conflict site between English and Spanish vowels has to do with the fact that Spanish vowel quality and duration is not affected by lexical stress, while there are differences in vowel quality and duration in English between tonic and atonic vowels [
61]. The results of this study suggest that the introduction of English via code-switching produces statistically significant differences in the vowel quality between the two language sessions; this is to say, Spanish vowels after a code-switch from English into Spanish are influenced by the English that preceded them, provoking a change in their normalized F1 and/or F2 values.
Furthermore, our study adds empirical evidence to Simonet’s hypothesis that transient interference should be more likely to occur in bilingual mode than in monolingual mode due to the activation of both languages in the bilingual speaker [
39]. While Grosjean argues that it may be difficult to distinguish between interference and transfer [
38], we concur with Simonet’s assessment that within-speaker comparisons (i.e., between monolingual and bilingual mode) can be utilized to investigate transient effects [
39]; furthermore, we would propose that comparisons between a bilingual speaker’s productions in monolingual mode and productions from a monolingual speaker of that language would be a way to examine Grosjean’s idea of transfer (i.e., permanent effects of one language on the other) [
38]. Consequently, future research investigating transfer effects should compare the phonetic productions of monolingual Mexican Spanish speakers to those of HSs.
The second part of the first research question dealt with whether there were effects of lexical stress on Spanish vowel quality. The linear mixed effects models revealed that there were statistically significant differences between tonic and atonic vowels with the normalized F1 (i.e., for /a/, /e/, /o/) and normalized F2 (i.e., /i/, /o/ and /u/) values. Similar to the results for language session,
Figure 3 showed that the mean values for the tonic vowels are found on the outer edges of the vowel chart, while the mean values for the atonic vowels are found in the central space of the chart. This finding parallels the results from Ronquest [
16], who also found significant differences in the vowel quality of Spanish HS stressed and unstressed vowels, even though the study was conducted entirely in Spanish. This is to say, the present study and Ronquest [
16] both provide initial evidence that English may affect the Spanish HS vocalic system, although we concur with Ronquest [
16] in noting that English may not be the sole explanation of the data in light of the fact that /e/ and /o/ in atonic position were slightly more raised than their tonic counterparts.
The second research question of the present study was concerned with the effect of code-switching and lexical stress on Spanish HS vowel duration. Our results show that lexical stress, and not code-switching, significantly affected vowel duration. More specifically, the results confirmed our hypothesized direction of influence, in that unstressed vowels were statistically shorter in duration than vowels in stressed syllables. Again, this result mirrors those found by Ronquest [
16], as this study found significant differences for four of the five Spanish HS vowels in the same direction. The results from both of these studies point to a possible English influence on Spanish, given that unstressed vowels in English are quantitatively shorter in duration than vowels in stressed position.
With respect to the effect of the distance from the code-switching site and Spanish HS vowel quality (i.e., the third research question) and duration (i.e., the fourth research question), we did not find a statistically significant effect. While we concur with previous research [
41] that distance from the code-switching site is a factor that should be examined with phonetic productions of bilinguals, our lack of evidence for its importance may be due to the fact that we limited the number of vowels taken after the code-switch to five. This is to say, it is possible that there was still a high level of activation from English during the production of these five vowels after the code-switch; future research should consider expanding the number of tokens taken after the code-switching site to see if there is a statistically significant effect of the distance from the code-switching site on normalized F1, normalized F2, and vowel duration values.
Overall, the present study has provided evidence that Spanish HS vowels may not be the same as their monolingual counterparts, which adds to the general HL research in this area [
25,
26,
27,
28,
29,
31]. However, without a comparison group of Mexican monolingual Spanish speakers from the same region as our participants’ families, we can only claim that our HSs are different from what has been reported in descriptions of the Spanish language [
34,
35]. However, by comparing vowels from a monolingual session to vowels from the code-switching session, we are able to say that the introduction of a Spanish HS’s other language influenced their vocalic productions. This finding concurs with the bilingual language modes framework [
38] and Simonet’s [
39] empirical work, in that the activation of a language that reduces vowels (i.e., English), in terms of both vowel quality and duration, affected the productions of a language in which vowel reduction should not occur (i.e., Spanish).
While the present study has provided evidence that code-switching affects Spanish HS vowel production, as well as corroborating previous research [
16] with respect to lexical stress, this study also raises some additional questions for future research. For example, the majority of the current research on Spanish HS phonetic production has employed experimental methods [
16,
25,
26,
27,
28,
33,
36,
40,
43,
53,
62,
63] including the present study. Therefore, there is an open question about the role of task effect in these studies, as they might be different within more naturalistic contexts; future research should consider exploring Spanish HS phonetics with tasks that elicit more spontaneous data, such as sociolinguistic interviews.