Highlights

• • It has been suggested that the parents of heritage speakers (2nd generation immigrants), who are the main source of input to them, may exhibit first-language (L1) attrition in their language, thereby directly transmitting different structural properties or “errors” to the heritage speakers.

• • This is unlikely: Language attrition in adults is rare, while structural changes in heritage speakers are very common.

• • Like L1 children, heritage speakers do not directly replicate the input from the parents.

• • Structural divergence between child and adult grammars are not necessarily related; they arise independently.

• • If the patterns evident in heritage speakers and first-generation immigrants are related, reverse transmission may be at play instead, when the heritage speakers might be influencing the language of the parents rather than the other way around.

2. Direct language transmission?

To what extent can many of the divergent structural patterns observed in heritage speakers be related to similar patterns in the first-generation immigrants who are the parental generation? The idea seems to be that many first-generation immigrant adults who are living in a language contact situation show native language attrition and interact with other bilinguals in their communities, including their children. To give a concrete example, the distribution of null and overt subjects has been extensively discussed in L1 attrition studies (Domínguez & Hicks, Reference Domínguez, Hicks, Cuza, Czerwionka and Olson2016; Gürel, Reference Gürel2004; Tsimpli et al., Reference Tsimpli, Sorace, Heycock, Filiaci and Bouba2003), and the main finding has been that speakers of null subject languages overextend overt subjects in pragmatic contexts where null subjects are more felicitous, such as in topic continuity or same reference contexts (Sorace, Reference Sorace2011). If adult immigrants who speak a null subject language (Spanish, Greek, Italian) show, say, 5% overproduction of overt pronominal subjects in same reference contexts due to attrition, heritage speakers are likely to show twice or thrice that rate, to give an estimate, of the same divergent pattern (see Montrul, Reference Montrul2018b for an example with null and overt subjects in Spanish; see also Labov, Reference Labov2007 for a similar explanation for sound changes). The generalized interpretation has been that first-generation immigrants’ attrition patterns are transmitted directly to the second-generation speakers (the heritage speakers), who in turn amplify the extent and magnitude of the changes.

For a language to be transmitted across generations, an obvious relationship must exist between the language of the parents (or adult caregivers) and the language of the children. For instance, sociolinguistic studies have linked the speech of adults and children, as with the pronunciation of /ou/ in southern British English, where young children model the pronunciation of one or both parents (Kerswill, Reference Kerswill1996). In Lightfoot’s (Reference Lightfoot1991) and Yang’s (Reference Yang2000) accounts of language acquisition and language change, there is a direct link between the language produced by the parents (E-language) and the internalized grammar (I-language) of the children to account for language transmission, as in Figure 1. E-language has no internal structure; structure is assigned to it through parsing by the child’s I-language (Lightfoot, Reference Lightfoot2020).

Figure 1. The dynamics of language acquisition and change (Yang, Reference Yang2000, p. 232).

A well-known proposal in diachronic change is that when young children somehow fail to parse the parental input, a process of reanalysis and restructuring that gives rise to a different, divergent grammar ensues (Lightfoot, Reference Lightfoot1991, Reference Lightfoot2020; Pires & Thomason, Reference Pires, Thomason, Ferraresi and Goldbach2008). In essence, change occurs because there is a break in transmission, and the language of the parents and the language of the children diverge with respect to a particular property (e.g., case marking, V2, null subjects). “When E-language shifts, children may parse differently, and thus a new I-language emerges” (Lightfoot, Reference Lightfoot2020, p. 29.)Footnote ¹

However, child monolingual (L1) learners have been shown to be very conservative during early development and make very few errors (Aitchison, Reference Aitchison2003; Snyder, Reference Snyder2017). So, they are unlikely to experience the amount of parsing failure leading to language change. For this reason, both Meisel et al. (Reference Meisel, Martin and Rinke2013) and Westergaard (Reference Westergaard, Janda, Joseph and Vance2021) have raised credible objections on the purported link between monolingual acquisition and diachronic language change, maintaining instead that language contact through second (L2) acquisition or bilingualism in the parental generation brings about changes in the E-language that is the input to the I-language of their children. Their position bodes well with the consensus in sociolinguistics (Bentz & Winter, Reference Bentz, Winter, Wichmann and Good2014; McWhorter, Reference McWhorter2007; Meisel et al., Reference Meisel, Martin and Rinke2013; Trudgill, Reference Trudgill2001): that adult L2 learners are the main agents of language change because L2 acquisition generally results in non-native attainment after puberty (Johnson & Newport, Reference Johnson and Newport1989; Hartshorne et al., Reference Hartshorne, Tenenbaum and Pinker2018).

Leaving aside for now the issue of diachronic language change, I want to bring attention to the idea of successful transmission (Figure 1); that is, when the output of the parents’ grammars feeds the developing system of the children’s grammars, and the children and the parents end up sharing approximately the same I-grammars across generations. A child exposed to English acquires English; a child exposed to Mandarin acquires Mandarin. This is what happens in typical language acquisition in general, when new, different patterns do not emerge in the younger generation. While heritage speakers exposed to Spanish, or Russian, or Korean acquire Spanish, Russian or Korean, respectively, it has been repeatedly claimed that the heritage speakers who show errors, divergent attainment, innovations, or changes in their heritage language do so because of direct transmission (and supposedly exact “replication”, as in Sankoff, Reference Sankoff2019) of structural patterns from the parental generation, as in Figure 1. For example, responding to Montrul and Polinsky’s (Reference Polinsky2011) commentary on the extension of the Interface Hypothesis to study heritage speakers, Sorace (Reference Sorace2012, pp. 213–214) writes:

And in a commentary on Hicks and Domínguez’ (Reference Hicks and Domínguez2020) model of L1 attrition, Sorace (Reference Sorace2020), pp. 203–204) amplifies the same claim:

That heritage speakers may be exposed to qualitatively different input compared to monolingual children is possible and true, but Sorace’s claim that such qualitatively different input “is transmitted” and becomes intake to heritage speakers’ developing systems (i.e., my interpretation of direct transmission) is an entirely different possibility. The studies cited by Sorace (Reference Sorace2011)—Pires and Rothman (Reference Pires and Rothman2009), Place and Hoff (Reference Place and Hoff2011) and Unsworth et al. (Reference Unsworth, Argyri, Cornips, Hulk, Sorace and Tsimpli2011)—provide evidence that heritage speakers may be generally exposed to qualitatively different input, but nothing else: They are not about how the language of the parents affects the heritage language of their children.

Still, theoretically, direct transmission of grammatical changes is in principle possible, but how common is it, and has it been attested? After many years of living in the United States, some first-generation immigrants can also exhibit signs of language attrition in some aspects of their grammars. Although most studies of attrition have found optionality due to lexical access and processing effects, as the quote from Sorace (Reference Sorace2020) above suggests, in my work with Spanish speakers in the United States, I have found evidence of attrition at the level of linguistic representations, not just processing, with differential object marking (DOM) and related syntactic structures, as measured by a variety of comprehension, production and judgment tasks (Montrul, Reference Montrul2019, Reference Montrul2022). I assume that attrition in heritage speakers and in the first generation of immigrants leads to structural changes and different endstate grammars. DOM is the phenomenon by which animate, specific direct objects are overtly marked with the preposition “a” in Spanish. Several studies have found that heritage speakers of Spanish largely omit this marker (Arechabaleta Regulez, Reference Arechabaleta Regulez2019; Cuza et al., Reference Cuza, Miller, Pérez Tattam and Ortiz Vergara2019; Montrul, Reference Montrul2004; Montrul & Bowles, Reference Montrul and Bowles2009; Thane, Reference Thane2024). Montrul and Sánchez-Walker (Reference Montrul and Sánchez-Walker2013) compared child heritage speakers to age-matched monolingual children in Mexico, and adult heritage speakers to age-matched monolingual native speakers in Mexico and first-generation immigrants in the United States. There was a significant omission of DOM (35%) by the bilingual children, whereas the monolingual children and adults tested in Mexico were at ceiling (above 98%). The adult heritage speakers omitted more DOM (20%) than age-matched native speakers in Mexico. As for the bilingual immigrant adults, about half of them omitted DOM like the heritage speakers (ranging from 10% to 70% omission). It is easy to conclude from these findings that many adult heritage speakers may be receiving attrited input from the adult immigrants because the same phenomenon was found in the two groups. In fact, this is the conclusion reached by Grosjean and Py’s (Reference Grosjean and Py1991) studies of first and second-generation Spanish-speaking immigrants in French Switzerland, who also found incorrect acceptance of omission of DOM and other structures in a grammaticality judgment task and suggested that morphosyntactic changes in the first generation pass over to the second generation.

Montrul (Reference Montrul and Pascual y Cabo2016b) is another study of the same adult participants in Montrul and Sánchez-Walker (Reference Montrul and Sánchez-Walker2013), about the preposition “a” as an obligatory dative marking with dative experiencer verbs like gustar “like” ( A Juan le gusta cantar “Juan likes to sing”). Spanish heritage speakers have been found to omit the dative case marking with these verbs, producing and preferring nominative experiencers as in English (*Juan (le) gusta cantar) (Montrul, Reference Montrul2014; de Prada Pérez & Pascual y Cabo, Reference de Prada Pérez and y Cabo2011; Toribio & Nye, Reference Toribio and Nye2006). Montrul (Reference Montrul and Pascual y Cabo2016b) used an acceptability judgment task and a written production task. Ungrammatical sentences without the preposition “a” were judged as statistically more acceptable than other ungrammatical sentences. In the written production task, some participants omitted the “a” with gustar-type verbs between 15% (the adult immigrants) and 20% (the heritage speakers), whereas the native speakers from Mexico did not omit a-marking with the psych verbs in written production. Montrul (Reference Montrul and Pascual y Cabo2016b) concluded that because the first-generation immigrants are the main source of input to the heritage speakers, the structural properties of the output of the first generation may reinforce, not necessarily feed directly, the mental representations of the individual grammars of the second generation, which may also be affected by majority language transfer.

Pascual y Cabo (Reference Pascual y Cabo2013, Reference Pascual y Cabo2020) also argued that linguistic innovations in heritage speaker grammars with gustar-type verbs can be traced back to subtle changes in the input received from first-generation immigrants, especially when production data are considered. The hypothesis investigated was that heritage speakers have reanalyzed dative experiencer verbs as nominative experiencer verbs, which would lead them to accept passive structures with gustar-type verbs. Pascual y Cabo found that only the heritage speakers accepted ungrammatical passives with gustar-like verbs in the grammaticality judgment task. In the production task, some omission of “a” was produced by monolingual adult (13.31%), bilingual adults (23.17%), advanced proficiency heritage speakers (29.21%) and intermediate proficiency heritage speakers (48.37%). Because all groups omitted “a” to some extent, Pascual y Cabo concluded that heritage language acquisition outcomes could result from differences in the input heritage speakers receive, following Pires and Rothman (Reference Pires and Rothman2009). However, Pascual y Cabo also considered that passivization of gustar-verbs can come from direct transfer from English, which affects the heritage speaker groups more than the first-generation bilingual adults.

Despite these assertions, direct transmission of attrited patterns from the parents to the children is highly unlikely, for the following reasons:

1. 1) Language attrition in adults at the level of linguistic representations, especially at the morphosyntactic level, has been very hard to find (Schmid, Reference Schmid2013). There are some reported cases (Kasparian et al., Reference Kasparian, Vespignani and Steinhauer2017; Kasparian & Steinhauer, Reference Kasparian and Steinhauer2017; Montrul et al., Reference Montrul, Bhatt and Girju2015, Reference Montrul and Pascual y Cabo2016b), but they are very few. Most studies have found L1 attrition in lexical access, phonetics/phonology, and some syntactic preferences (Schmid, Reference Schmid, Schmid and Köpke2019). In general, language attrition is a highly individual phenomenon and quite rare (Hicks & Domínguez, Reference Hicks and Domínguez2020, cf. Schmid & Köpke, Reference Schmid and Köpke2017). By contrast, grammatical changes in heritage speakers are very extensive and remarkably common.

2. 2) Related to (1), most studies of intergenerational transmission comparing heritage speakers and first-generation immigrants show a break in transmission. First-generation speakers are at ceiling and do not differ from speakers in the homeland; heritage speakers are statistically different from first-generation immigrants, showing changes in lexical access in Dutch (Hulsen, Reference Hulsen2000), evidentiality markers in Turkish (Karayayla, Reference Karayayla2020), VOTs in Russian and Ukrainian (Nagy & Kochetov, Reference Nagy, Kochetov, Siemund, Gogolin, Schulz and Davydova2013), verb tenses, copulas, null and overt pronouns in Spanish (Silva-Corvalán, Reference Silva-Corvalán1994), DOM and dative clitics in Spanish (Irizarri van Suchtelen, Reference Irizarri van Suchtelen2016); accusative clitics in European Portuguese (Flores & Rinke, Reference Flores and Rinke2020; Rinke & Flores, Reference Rinke and Flores2014); case in Polish, Russian and Ukrainian (Łyskawa & Nagy, Reference Łyskawa and Nagy2020), to name just a few.

3. 3) Some of the patterns found in heritage language speakers are also found in second language (L2) learners, even those L2 learners exposed to native input. For example, L2 learners of Spanish omit DOM in obligatory contexts as much as heritage speakers of Spanish (Arechabaleta Regulez, Reference Arechabaleta Regulez2019; Guijarro-Fuentes & Marinis, Reference Guijarro-Fuentes and Marinis2007; Guijarro-Fuentes, Reference Guijarro-Fuentes2012). Case marking in general is difficult for heritage speakers of Hindi, Korean and Samoan; it is also difficult for L2 learners of Hindi (Montrul, Reference Montrul2019), Korean (Chung, Reference Chung2020) and Samoan (Muāgututi’a, Reference Muāgututi’a2018). This suggests internally driven developments in different bilingual grammars converging on a common result, independently of input quality.

4. 4) During early stages of language development, children make errors (overgeneralizations of morphology, case omissions, under or overproduction of null/overt subjects, determiners or other pronouns, for instance) that are internally motivated by the current state of the children’s developing grammars and other cognitive resources (working memory, parsing routines, etc.) because their caregivers do not produce such errors (Crain, Reference Crain1991; Guasti, Reference Guasti2002; Lidz & Gagliardi, Reference Lidz and Gagliardi2015; Pinker, Reference Pinker1989). If heritage speakers are native speakers and learn their heritage language like L1-acquiring children (Montrul, Reference Montrul2013, Reference Montrul2022; Rothman & Treffers-Daller, Reference Rothman and Treffers-Daller2014), why would they be different?

Rather than parental transmission of structural patterns, I argue instead for a break in transmission, as in diachronic language change: In essence, structural changes in heritage grammars arise mostly (but not exclusively) from internal reanalysis of the heritage language grammar due to insufficient input (Montrul, Reference Montrul2016a, Reference Montrul2022; Polinsky, Reference Polinsky2018). Under Lightfoot’ (Reference Lightfoot2020) proposal that parsing and acquisition are the same construct, the changes arise because the I-language of the heritage speakers may not fully parse the E-language from the parents with all its finer morphosyntactic details, not necessarily because the E-language provided by the parents may have changed, but because the quantity of input is insufficient to internally trigger certain parsing routines. Insufficient input during a critical age in language development leads to psycholinguistic effects such as fuzzy linguistic representations and difficulty accessing the linguistic representations of the heritage language for production and comprehension (Putnam & Sánchez, Reference Putnam and Sánchez2013; Montrul, Reference Montrul2021). In recent studies of school-age heritage speakers, we have found that when the heritage language is the medium of instruction at school, such exposure enhances cue integration during processing and acquisition (Armstrong, Reference Armstrong2024; Montrul & Armstrong, Reference Montrul, Armstrong and Batbasouli2024).

As for the very few instances where we see incipient morphosyntactic changes in the first generation that are amplified in the heritage speakers (Montrul & Sánchez-Walker, Reference Montrul and Sánchez-Walker2013; Montrul, Reference Montrul2016a, Reference Montrul2022; Pascual y Cabo, Reference Pascual y Cabo2020), these changes most likely develop independently in the two groups (see also Putnam et al. Reference Putnam, Kupisch, Pascual y Cabo, Miller, Bayram, Rothman and Serratrice2018), because the age of acquisition and the flexibility of the linguistic competence after a certain age play a critical role in language change (Kerswill, Reference Kerswill1996; Montrul, Reference Montrul2022; Sankoff, Reference Sankoff2019). If one generation affects the other, I suggest it is the adult heritage speakers who may contribute to changes in the language of the parents. For parents to directly transmit L1 attrition patterns to their children, the age of the children is critical to parse the input, as I discuss next.

3. Interrupted transmission

Both generative approaches to language acquisition and the variationist sociolinguistic concept of generational change share the assumption that the linguistic knowledge of the individual stabilizes and becomes firmly established and consolidated after childhood (Labov, Reference Labov2001, pp. 448–552). Before puberty, the linguistic knowledge of children is nimble. After puberty, linguistic patterns become entrenched. For this reason, if linguistic innovations occur in the parental generation during the heritage speakers’ childhood years (pre-adolescence), language change is more likely because children’s linguistic ability is malleable and flexible (see Mayberry & Kluender, Reference Mayberry and Kluender2018 and Birdsong, Reference Birdsong2018 for the relationship between language development, age and brain plasticity). For instance, Lightfoot (Reference Lightfoot2020) claims that changes in reduced verb morphology in the primary linguistic data (adult E-language) led 3-year-old children in the Middle English period to parse English verbs into different categories. Meisel et al. (Reference Meisel, Martin and Rinke2013) also contend that the age of the language learner and the psycholinguistic mechanisms that mediate between the I-language and the E-language is what links L2 acquisition and language change.

As discussed earlier, the literature on diachronic linguistics has made the monolingual child the prototypical agent of language change (Lightfoot, Reference Lightfoot1991, Reference Lightfoot2020; Lightfoot & Westergaard, Reference Lightfoot and Westergaard2007). While children do acquire the language of their environment and do not stray very far from what they hear, they do not always reproduce what they hear in the input faithfully (Shin & Miller, Reference Shin and Miller2022) because they are constrained by their cognitive and psycholinguistic capacities. Unlike their parents and adult interlocutors, children simplify phonological clusters, omit required morphology (Snyder, Reference Snyder2021), overgeneralize regular morphology to irregular forms, and overgeneralize other syntactic patterns with different verb placement (Westergaard, Reference Westergaard, Manaffert, Bull and Killie2005) or wh-words (Thornton, Reference Thornton1995). For example, Hudson Kam and Newport (Reference Hudson Kam and Newport2005) taught children ages 5–7 an artificial language. They then presented the children with input for that language with either consistent use of the determiner (i.e., nouns occurring with the same determiner 100% of the time) or inconsistent use (i.e., nouns occurring with different determiners at different frequencies). Unlike the adults tested who reproduced the input veridically, many children regularized the language, imposing patterns that were not the same as what they had been exposed to in their input. These results suggest that children and adults do not learn from variable input in the same way and that children do not faithfully reproduce the input.

In situations where children could be exposed to inconsistent or variable input, such as when the parents are non-native speakers of the majority language, children do not always adapt toward the non-native patterns of their parents. Creolization studies have shown that children who receive only pidgin input develop a more complex and regularized grammar (Bickerton, Reference Bickerton1984; Senghas, Reference Senghas1995), providing some of the strongest evidence that children go beyond their input in the process of acquiring a native language. Other compelling examples come from sign languages, where children surpass their parents’ L2-accented input and become native signers (Singleton & Newport, Reference Singleton and Newport1994). At the same time, this empirical evidence does not deny altogether a potential link between child language and the caregiver model, including some changes that may be going on in the adult model; my claim is simply that not all changes or differences in the adult parental model are adopted by the children.

Heritage speakers also surpass the input from their parents in their command of the majority language. In most of the studies I have conducted on heritage speakers to date, my participants have had very advanced to native-like command of English, reflected both in proficiency measures and linguistic tasks on unaccusativity (Montrul, Reference Montrul2006) and the semantics of definite determiners in Spanish and English (Montrul & Ionin, Reference Montrul and Ionin2012). In the studies reported in Montrul (Reference Montrul2022), the Romanian heritage speakers and the Spanish heritage speakers had higher self-rated proficiency in English than the first-generation immigrants. Surpassing the adult non-native model is possible in these cases because heritage speakers are exposed to the majority language in childhood, they have access to the language in the community, which includes many other native speakers and are schooled in the majority language.

But let us consider the possible developmental scenarios of the minority, heritage language and the issue of timing of variable, inconsistent input, if such inconsistent input were available to the heritage speakers and they replicated it veridically (which they typically do not). We will see that when we compare the language learning and forgetting trajectories of children and their parents, assuming families are having children within the first 10 years postmigration, the timing of attrition in adults and the timing when developing child grammars are malleable do not match in such a way that the parental generation could possibly directly influence the children in the manner that it has been suggested.Footnote ³

L1 attrition in adult immigrants at the level of linguistic representations (Hicks & Domínguez, Reference Hicks and Domínguez2020; Schmid, Reference Schmid2011; Schmid & Köpke, Reference Schmid and Köpke2017) is rare, and when it occurs, it only affects a handful of individuals. Typically, studies have detected measurable effects of attrition in morphosyntax with immigrants with a LOR beyond 10 years (Gürel, Reference Gürel2004, cf. Chamorro et al., Reference Chamorro, Sturt and Sorace2015). The Mexican immigrants who showed morphosyntactic attrition reported in Montrul et al. (Reference Montrul, Bhatt and Girju2015) and Montrul (Reference Montrul2022) (n = 21) had a mean LOR in the United States of 19.5 years compared to 9.12 years in the Romanian immigrants. Those Mexican immigrants who showed omission of DOM were older (mean 48.3 versus mean 43.2), had been in the United States longer than the ones who did not omit DOM (27.3 years versus 23.1 years) and had acquired English later in life (22 versus 20.2). The two immigrants with the lowest accuracy on DOM (both 33%) had been in the United States for 33 and 37 years, respectively. Figures 2 and 3 show their acceptability of ungrammatical sentences in Spanish, with the omission of DOM (Figure 2) and acceptance of accusative clitic doubling (Figure 3), which is ungrammatical in Mexican Spanish (but grammatical in other varieties).

Figure 2. Relationship between length of residence in the U.S. and acceptability of ungrammatical animate specific direct objects without DOM by the adult Mexican immigrants (Montrul, Reference Montrul2022). A linear mixed-effects model revealed that this correlation was significant (SE = .01, β = .03, p < .05).

Figure 3. Relationship between length of residence in the U.S. and acceptability ratings on animate definite objects with clitic doubling by the adult Mexican immigrants (Montrul, Reference Montrul2022). The output of the model showed that there was a significant correlation between LOR and acceptability of the target construction (SE = .01, β = .02, p < .05).

These data show that it takes several years of immersion in the second language and restricted input and use of the native language for attrition to be detected in oral production and grammaticality judgment tasks. However, some native speakers may start to show changes in lexical access as soon as they start L2 acquisition (Bice & Kroll, Reference Bice and Kroll2015), suggesting that changes in processing before changes in production are possible but hardly permanent (see also Chamorro et al., Reference Chamorro, Sorace and Sturt2016). By the time adult immigrants start showing non-native patterns in their language production, comprehension and grammaticality judgments of morphosyntax, as in the studies reported in Montrul (Reference Montrul2022), their children have probably well passed the period when they were most likely to be influenced by the parental input, i.e., preadolescence. Of course, this proposal raises several questions: When exactly do heritage speakers begin influencing their parents? Do heritage speakers initiate the change in the parental generation, or do they simply reinforce incipient variability in the parental generation? Is there a way to tease apart changes in the parental generation due to LOR in the host country versus heritage-speaker-initiated changes?

Considering studies on DOM, monolingual children show some variability with DOM (about 20–25% omission depending on the language), before age two or three (Coşkun Kunduz & Montrul, Reference Montrul2021; Ticio & Avram, Reference Ticio and Avram2015). Studies of DOM with bilingual children have shown that DOM lags in development very early; the earliest data we have is from 3-year-olds (Ticio, Reference Ticio2015), who produce DOM about 25% of the time (i.e., 75% omission) (but see Requena, Reference Requena2023’s reanalysis of these data). Montrul and Sánchez-Walker (Reference Montrul and Sánchez-Walker2013) showed that children ages 6–14 (mean 11) continue to show very high rates of DOM omission (almost 40%). This means that children are omitting DOM when they are younger, and during that time, the parents may be producing DOM at ceiling. Some variability and DOM instability before age three is part of the developmental picture in monolingual and bilingual acquisition. The problem is what happens after age three, when bilingual development now appears to lag. So, the developmental trajectories of partial, interrupted acquisition in children (heritage speakers) and attrition in adults (parents or other caregivers) do not match, as illustrated in Figure 4. Therefore, as bilingual children are growing up, if they show nontarget development between preschool and middle school, it is highly unlikely a result of their parents’ input.

Figure 4. Possible developmental trajectories of L1 acquisition, L1 attrition and acquisition in heritage speakers and their caregivers.

One way to test this hypothesis is to directly compare the linguistic knowledge of heritage language children and that of their parents. If the parents show almost ceiling production while the children show extensive variability, then it is difficult to link the grammars of the children (I-language) to the parents’ production (E-language).

4. Empirical evidence

Recent studies have focused on how children acquire the heritage language across the school-age years (Chondrogianni & Schwartz, Reference Chondrogianni and Schwartz2020; Daskalaki et al., Reference Daskalaki, Blom, Chondrogianni, Paradis and Daskalaki2020; Flores et al., Reference Flores, Santos, Jesus and Marques2017; Jia & Paradis, Reference Jia and Paradis2015). Some have tested heritage language children and their parents. Cuza et al. (Reference Cuza, Miller, Pérez Tattam and Ortiz Vergara2019) elicited the oral production of DOM in SVO matrix sentences (Llamé a mi abuela, “I called my grandmother”) and in sentences with clitic left dislocations ( A mi abuela la llamé, “My grandmother, I called”) in Spanish-speaking monolingual and bilingual children ages 5–11 (mean 8;2), and in the Mexican parents of the bilingual children with a mean LOR in the United States of 13.8 years. The monolingual children and the bilingual parents were at ceiling, but the heritage language children omitted DOM 35% of the time. Cuza et al. (Reference Cuza, Miller, Pérez Tattam and Ortiz Vergara2019) did not find L1 attrition of DOM in the parents tested; DOM was present in the children’s input 99% of the time. There were no age differences within the bilingual children: older children did not omit DOM more than younger children, which also supports the observed “stability” of this phenomenon in different bilingual samples (Montrul & Sánchez-Walker, Reference Montrul and Sánchez-Walker2013).

Similar findings are reported by Coşkun Kunduz and Montrul (Reference Coşkun Kunduz and Montrul2022), who investigated DOM in Turkish heritage language children (ages 7–14) and their parents in the United States. Turkish native speakers in Turkey were tested to establish whether the adult Turkish first- generation immigrants in the United States manifested L1 attrition. A group of adult heritage speakers in the United States (second-generation immigrants) were included to see whether omission of DOM could be attributed to L1 attrition in the adult heritage speakers (as in Polinsky, Reference Polinsky2011). The Turkish immigrants performed at ceiling in two oral tasks, like the native speakers in Turkey. However, both the child and adult heritage speakers showed extensive variability and omission of accusative case marking with specific direct objects, which is the way that Turkish instantiates DOM. Correlation analyses of child–parent dyads found no relationship between the language of the parents and the language of the children, suggesting no evidence of L1 attrition directly impacting the omission patterns found in the children and in the adult heritage speakers. In a related study with the same participants and tasks, Coşkun Kunduz and Montrul (Reference Coşkun Kunduz and Montrul2023) tested the production and comprehension of evidentiality markers –DI and–mIş Footnote ⁴, another feature that has been found to be vulnerable in adult heritage speakers of Turkish (Karayayla, Reference Karayayla2020). Another group of very young Turkish speakers in Turkey (3–6 year-olds) was included to establish when in monolingual acquisition Turkish children know the difference between the two evidentiality markers depending on whether the source of information is direct (-DI) or indirect (–mIş). Results revealed weak mappings between the indirect evidential marker –mIş and its pragmatic use in storytelling as opposed to intact knowledge of the Turkish evidentiality system in the first-generation immigrant group. The child and adult heritage speakers, on the other hand, were the least accurate groups in both tasks, performing even more variably than the 3–6-year-old monolingual children in Turkey. The individual analysis of the child heritage speaker data as well as a comparison of the child–parent dyads confirmed that the nature of the parental input is an unlikely source of the variability observed in children and eventually in adult Turkish heritage speakers.

Another study showing little relationship between the linguistic knowledge of first-generation immigrants and their children (second-generation) is Daskalaki et al. (Reference Daskalaki, Blom, Chondrogianni, Paradis and Daskalaki2020), who studied subject positions in Greek heritage language children in Canada (most second-generation but a few third-generation immigrants) and their parents, as well as an age-matched group of monolingual children and parents in Greece. Postverbal subjects are obligatory in Greek interrogative sentences, while in declarative sentences and in wide focus contexts, postverbal subjects are variable and depend on semantic and pragmatic conditions. The child monolinguals and their parents were all at ceiling (99%) in an elicited production task. Whereas the heritage children showed an overall accuracy of 45% and produced more infelicitous preverbal subjects than postverbal subjects in wide focus than in embedded questions, the first-generation immigrant parents were very accurate. Results from second-generation parents and third-generation children were different because the parents did show some variability and their children even more. This study shows that the parental input to monolingual children can be different from the parental input to bilingual children for the parents who are themselves heritage speakers, but most importantly, they also refute the hypothesis that second-generation heritage speakers receive attrited input from their parents.

Requena and Dracos (Reference Requena and Dracos2021) examined second-generation Spanish-English bilingual children ages 5–14 (heritage speakers) to determine whether they interpret Spanish copulas ser and estar with adjectives like first-generation adults in their community. Some adjectives can be used with either copula, but there is a semantic and pragmatic aspectual distinction. Estar is specified for aspectual properties (Schmitt & Miller, Reference Schmitt and Miller2007), while ser is unspecified for aspect. By age 4 monolingual Spanish speakers have acquired the semantic and pragmatic interpretation of the two copulas (Requena, Reference Requena2021). Adult heritage speakers of Spanish have been shown to extend estar to uses of ser (Silva-Corvalán, Reference Silva-Corvalán1994; Geeslin & Guijarro-Fuentes, Reference Geeslin and Guijarro-Fuentes2008), and the two Spanish-English bilingual children followed longitudinally by Silva-Corvalán (Reference Silva-Corvalán2014) from ages 1;00 to 6;00 also showed extensions of estar to ser contexts. Requena and Dracos (Reference Requena and Dracos2021) investigated the effects of age, language exposure/use, and proficiency on copula selection. Some of the adults were the parents of the children, so their language can be considered representative of the input to the children. In a picture selection task, the adults showed much higher selection of the temporary picture with estar (92%) compared to the children (67%). For the children, higher Spanish proficiency increased the selection of the picture with estar and decreased the preference for ser. The low-proficiency children were at chance like the 3-year-old children in Requena’s (Reference Requena2021) L1 acquisition study. Even though they did not exhibit exact adult-like usage, high-proficiency children did exhibit knowledge of the semantics and pragmatics of the copulas. There is no basis to conclude that the low proficiency children are receiving attrited input from the parents.

Finally, Mai et al. (Reference Mai, Zhao and Yip2022) investigated knowledge and use of the Mandarin ba-construction through elicited narration in heritage Mandarin children ages 4–14 and their parents in the UK. Mandarin and English have basic SVO order, but in Mandarin SOV order is possible with the -ba construction, which takes the form ([(NP1)-ba-NP2-VP]) and is the preferred way native speakers express statements in disposal and causative contexts, as in (1). NP1 is the subject/topic and can be overt or null based on syntactic, semantic and discourse conditions independent of this construction. NP2 (qingua) is the object.

In monolingual acquisition, the ba-construction emerges around age 2 and becomes highly productive by 2;6 (Deng et al., Reference Deng, Mai and Yip2018). Adult heritage speakers have been found to underuse the ba-construction, preferring SVO sentences instead. Mai et al. (Reference Mai, Zhao and Yip2022) investigated the extent to which school-age Mandarin heritage children in the UK produced the ba-construction and how their productions compared to that of their parents, the input providers, in terms of (i) structural frequency, (ii) the linear structure of [(NP1)-ba-NP2-VP], and (iii) the types of nominal and verbal phrases used in NP2 and VP. All heritage language children and the parents narrated a frog story. No correlation was found between the children and the parents’ productions because the heritage children produced the ba-construction less frequently than their parents and used a more limited set of nominal and verbal phrases. None of the child–adult differences in the UK groups were attested in the children and adults tested in Beijing. Mai et al. concluded that the lower frequency of the structure and reduced diversity of the nominal and verbal phrases in the heritage children’s construction can only be attributed to the diasporic context in the UK, where input in the heritage language is significantly less abundant.

To summarize, all these recent studies comparing heritage language children and their parents on different linguistic phenomena converge on the same outcome: by school-age, structural patterns and frequency in the parental input no longer determine the children’s output. In all these cases, the parents are at or close to ceiling in their linguistic performance, as in the idealized grey solid line in Figure 4, while their children are not (dashed line). For school-age heritage children, hearing more utterances with DOM, evidential markers, subject position, copulas and the ba-construction from the parents does not necessarily boost their production or comprehension of all these structures. All these studies point to the conclusion that simplification in the children’s grammars most likely arises by how their internal grammars process and make do with insufficient input in the heritage language and cross-linguistic influence from the societal majority language before the closure of the critical period, when their native language representations are still nimble and malleable.Footnote ⁵

Finally, Requena and Dracos (Reference Requena and Dracos2021) also suggest that low-proficiency second-generation children are a catalyzing locus of accelerated language change observed by Silva-Corvalán (Reference Silva-Corvalán1994). Because there are a few reported cases of first-generation immigrants displaying some of the same patterns as second-generation immigrants (heritage speakers) (Montrul et al., Reference Montrul, Bhatt and Girju2015; Montrul, Reference Montrul2016a, Reference Montrul2022; Pascual y Cabo, Reference Pascual y Cabo2020), I suggest that attrition in the first generation of adults who have children may arise through reverse language transmission.

5. Reverse language transmission and language change

Montrul (Reference Montrul2014, Reference Montrul2022) made the novel proposal that heritage speakers are active agents in the diachronic evolution of Spanish as a distinct language variety of the United States. Although Meisel et al. (Reference Meisel, Martin and Rinke2013) argue that simultaneous bilingual children are like monolingual children and cannot be agents of language change, studies of child and adult heritage speakers show that simultaneous bilinguals can and do in fact fail to replicate the parental input, not because their language learning mechanisms are inefficient, as claimed to be for adult L2 acquisition past a critical period (Meisel, Reference Meisel2011), but because heritage speakers do not receive sufficient exposure to the heritage language during the critical period. Like Birdsong (Reference Birdsong2018), I use “critical period” as a generic term that also subsumes sensitive periods. Hartshorne et al.’s (Reference Hartshorne, Tenenbaum and Pinker2018, p. 12) results of L2 acquisition point to “a grammar-learning ability that is preserved throughout childhood and declines rapidly in late adolescence.”

Heritage speakers use the heritage language less frequently in late childhood and early adolescence than in early childhood, before the closure of the critical period, when the language capacity is still flexible and malleable. Less frequent use and activation of the heritage language leads to slow and taxing processing and parsing of the heritage language, under cognitive and social pressure from the majority language. Among the several factors that could explain the critical period, Hartshorne et al. also consider age-dependent changes in neural plasticity (see also Birdsong, Reference Birdsong2018; Mayberry & Kluender, Reference Mayberry and Kluender2018). Finally, Hartshorne et al. (Reference Hartshorne, Tenenbaum and Pinker2018) further found that bilinguals from birth were not entirely monolingual-like, which could also be attributed to the amount of language exposure rather than to timing of exposure, as I defend in this article. Birdsong (Reference Birdsong2018, p. 10) even writes: “Among international adoptees and heritage speakers, dominance shifts involve attrition of the L1, a representational and functional loss which likewise reflects neural plasticity.” Therefore, under certain circumstances, heritage speakers are driving the changes of their heritage language (not the majority language) which, when diffused or spread to other generations and speakers with different proficiency in the heritage language, creates a new variety of the language, in the same manner proposed for the diachronic evolution of standard languages with many non-native speakers (McWhorter, Reference McWhorter2007).

My claim that heritage speakers can be agents of language change because of the timing of acquisition (Figure 4) and when changes may spread is entirely consistent with sociolinguistics proposals that pre-adolescents are the main agents of language change (Tagliamonte & D’Arcy, Reference Tagliamonte and D’Arcy2009). Socio-psychological factors involving linguistic maturation and evolving social relationships have an impact on the way in which language change is transmitted (Fagyal et al., Reference Fagyal, Swarup, Escobar, Gasser and Lakkaraju2010). A recurrent finding from dialectal research is that children acquire the vernacular of their primary caretaker, most often the mother (Kerswill, Reference Kerswill1996; Kerswill & Williams, Reference Kerswill and Williams2000a; Labov, Reference Labov2001). Hence, the vernacular that children first speak is that of their female caregivers, and women have also been portrayed as leading linguistic changes (Labov, Reference Labov1989; Shin, Reference Shin2013). But upon school entry, children quickly adopt the vernacular of their peers, a critical stage in the incrementation of linguistic change (Labov, Reference Labov2001): the speech of 8-year-olds shows a striking departure from the speech of their parents in phonological processes, morphologically conditioned phenomena, and lexical rules (Kerswill & Williams, Reference Kerswill and Williams2000b). There is a weak correlation between linguistic features of 4-year-olds and their caregivers, but for 6–12-year-olds there is no correlation between caregiver and children’s features because the speech of the 6–12 year-olds accommodates to that of their peers, not their parents’. From this point on, social pressures encouraging conformity to peer group norms interact strongly with individuals’ declining ability to accommodate linguistically, at least in lexically complex processes, and probably, morphosyntax.

Between ages 12 and 17, past the critical period for language, children are essentially adults in terms of their abilities to acquire language, but in sociolinguistic variation, it is at this stage when some of the most dramatic changes seem to come about: “Adolescents are clearly significant agents of change; their social networks allow them to have wider contact than younger children, and their desire for a distinct social identity means that they are willing to modify their speech. At the same time, during this period (at age 16 at the very latest), they can no longer have the ability to acquire lexically complex rules, new oppositions or new intonational systems.” (Kerswill, Reference Kerswill1996, p. 198).

In situations of societal bilingualism where the heritage language is always threatened, as in Ireland (Gathercole & Thomas, Reference Gathercole and Thomas2009; Mueller Gathercole, Reference Mueller Gathercole2007), Fhlannchadha and Hickey (Reference Fhlannchadha and Hickey2021) found that changes in gender marking in Irish-speaking children (ages 6–13) were reflected in the adult input. But at this time in their linguistic development, heritage speakers of Irish have extensive exposure to input from L2 learners from-pre-school onwards in most educational settings. Jones (Reference Jones1998) found that Welsh children in immersion schools adopted the errors of the L2 learners of Welsh rather than influencing the L2 learners to use the correct form, or following the model provided by their parents, which did not show changes. Therefore, as heritage language children grow older, they do not necessarily adopt the speech patterns of their parents, if their social networks in the heritage language include other peers.

If adolescents are agents of language change, they provide us with a new way of understanding the mechanisms of language change in heritage languages, which points to different patterns of directionality of change and diffusion: parent-to-child (direct transmission), child-to-adult (backward transmission) and adult-to-adult. The studies found that both first-generation immigrants and second-generation heritage speakers omit DOM and dative case with psych verbs (Montrul & Sánchez-Walker, Reference Montrul and Sánchez-Walker2013; Montrul et al., Reference Montrul, Bhatt and Girju2015; Montrul, Reference Montrul2016a, Reference Montrul and Pascual y Cabob; Montrul, Reference Montrul2022; Pascual y Cabo, Reference Pascual y Cabo2020), overextend pronominal subjects in same reference contexts and preverbal subjects (Domínguez & Hicks, Reference Domínguez, Hicks, Cuza, Czerwionka and Olson2016; Montrul & Sánchez-Walker, Reference Montrul, Sánchez-Walker, Carvalho, Orozco and Shin2015; Otheguy & Zentella, Reference Otheguy and Zentella2012) and extend the copula estar to ser contexts (Requena & Dracos, Reference Requena and Dracos2021; Silva-Corvalán, Reference Silva-Corvalán2014) support the possibility of backward transmission in Spanish with respect to ongoing changes in the language. My proposed backward transmission (child-to-parent) is based on relating the age of the child during heritage language development, when input to the heritage language becomes progressively reduced, with how long it takes for L1 attrition to manifest in the parental generation (see Figure 2). A study comparing mothers and child heritage speakers as well as mothers and adult heritage speakers (Montrul, Reference Montrul2022, pp. 277–279) found that the mothers of both child and adult heritage speakers were largely at ceiling with the production of DOM in two oral tasks, and statistically more accurate than their own children. Accuracy on DOM in the child and adult heritage language groups ranged from 0% to 100%. There was incipient variability with DOM in 4 of 14 (28.5%) mothers of the adult heritage speakers, compared to 1 of 20 (0.5%) mothers of the child heritage speakers. So, the age of the children and the LOR of the parents must be considered in studies of child–parent dyads to understand this phenomenon.

Spanish-speaking adolescent and young adult heritage speakers influencing their parents would now be a case of adult-to-adult transmission since linguistically speaking, 17-year-olds and older are adults, as in Figure 5.

Figure 5. The dynamics of language acquisition and change in Spanish in the United States.

The teenage years are the time when many heritage speakers, who may now willingly embrace their heritage identity and are eager to regain contact with their language and culture, begin to use the language more with the parents at home. While progression of linguistic change slows in early adulthood, there are also suggestions that speakers participate in ongoing developments throughout the life cycle (Labov, Reference Labov2001; Shin & Otheguy, Reference Shin and Otheguy2013; Tagliamonte & D’Arcy, Reference Tagliamonte and D’Arcy2009), and this may be the reason why some of their adult parents’ speech (first-generation immigrants) starts to converge with the speech of their children, who show variability with respect to DOM, overt pronouns, dative case, copula selection and so forth. As pointed out by an anonymous reviewer, limited literacy may also contribute to accelerating language change in heritage speakers. Many, but certainly not all, heritage speakers are illiterate in their heritage language; their grammars being unconstrained by the effects of orthography and standardization efforts. Previous literature suggests that literacy safeguards against attrition, impeding or at least de-accelerating it in heritage language children (Zaretsky & Bar-Shalom, Reference Zaretsky and Bar-Shalom2010), and possibly in adulthood (Armstrong, Reference Armstrong2024). An input environment restricted to mainly the family supports a feedback loop leading to the possibility of the linguistic output of the second generation feeding the input to the first generation.

Therefore, Spanish heritage speakers contribute to shaping the variety of Spanish spoken in the United States. U.S. Spanish is made up of bilingual speakers with different bilingual profiles and different levels of proficiency: these include speakers of historical Spanish spoken in the region before the arrival of the English colonizers (e.g., New Mexico and other parts of the Southwest), Spanish-dominant speakers from Spain and Latin America, U.S.-born balanced Spanish-English bilinguals, English-dominant bilinguals and speakers of Spanish as a second language. Spanish-speaking families increasingly speak more English at home as children grow up but do not abandon Spanish (Hurtado & Vega, Reference Hurtado and Vega2004). As shift in language happens from Spanish to English and from one generation to the next, different levels of language use occur within the home domain, allowing exposure of Spanish to children and exposure of English to parents. Therefore, there are different levels or degrees of language use and exposure falling under the use of Spanish only or the use of English only, and the continuum in between. Heritage language speakers are an important segment of this population, and they contribute to shaping the variety of Spanish spoken in the United States. Increased use of subject pronouns (Otheguy & Zentella, Reference Otheguy and Zentella2012) and variable use of DOM with animate and inanimate objects are “stable” defining feature of U.S. Spanish, different from the variable use of null and overt subjects and DOM in other varieties of Spanish. A prediction this proposal makes, worthy of future research, is that adult Spanish-speaking immigrants in the United States who do not have children and do not frequently interact as much with heritage speakers should be spared from L1 attrition.