2.1 Explaining CLI: Overlap or co-activation?

An influential account that has shaped research into CLI in the past two decades is the overlap hypothesis advanced by Hulk and Müller (Reference Hulk and Müller2000). The authors propose two conditions for the occurrence of CLI in 2L1 bilingual development. First, language A has a single option for a given structure which overlaps (at least partially) with one of multiple structural options of language B. Second, the structures of interest are situated at vulnerable interfaces, particularly between syntax and discourse-pragmatics that are known to be problematic in monolingual L1 acquisition. Fulfilment of these two necessary (though not sufficient) conditions (Hulk & Müller, Reference Hulk and Müller2000, pp. 229) will make bilingual children's productions susceptible to overusing the crosslinguistically shared structure in language B, thus resulting in exclusively quantitative differences from monolingual children. CLI is expected to be unidirectional, affecting only the language with multiple options. Some of the research testing the overlap hypothesis across different language combinations is indeed consistent with its predictions (e.g., Döpke, Reference Döpke1998, Reference Döpke2000; Schmitz, Patuto & Müller, Reference Schmitz, Patuto and Müller2012). Other studies, however, have demonstrated CLI outside critical interfaces (e.g., Serratrice, Sorace, Filiaci & Baldo, Reference Serratrice, Sorace, Filiaci and Baldo2009), and in the absence of crosslinguistic overlap (e.g., Nicoladis, Reference Nicoladis2002, Reference Nicoladis2003; Yip & Matthews, Reference Yip and Matthews2000). At the same time, some studies have reported an absence of CLI when both linguistic conditions are met (e.g., Nicoladis et al., Reference Nicoladis, Rose and Foursha-Stevenson2010), thus undermining their predictive value.

An alternative proposal views CLI in early bilingualism as a result of co-activation during bilinguals’ online speech production process (Nicoladis, Reference Nicoladis2006; Nicoladis et al., Reference Nicoladis, Rose and Foursha-Stevenson2010). This account is based on speech production models (Ferreira & Dell, Reference Ferreira and Dell2000; Levelt, Roelofs & Meyer, Reference Levelt, Roelofs and Meyer1999) that assume several distinct stages of implicit decisions speakers make when realising an utterance. According to Nicoladis (Reference Nicoladis2006), CLI is presumed to occur as a result of co-activation during the stage of linguistic formulation (or lemma level), where the intended message from the first stage of conceptualisation is mapped onto language-specific forms, involving the selection of lexical items and syntactic frames. In bilinguals, the syntactic frames of both languages are always simultaneously co-activated to some extent, leading to competition. Based on this account, Nicoladis (Reference Nicoladis2006) explains bidirectional reversal errors observed in English–French bilingual children's adjective placement. Although only pre-nominal adjectives are shared crosslinguistically (e.g., une grande fille ‘a tall girl’), bilingual children also produced some target-deviant post-nominal adjectives in their English (e.g., apple green), which cannot be accounted for by the overlap hypothesis. Within a co-activation account, wishing to produce ‘green apple’ in English activates the lexicalisations and their associated syntactic frames in both languages. That is, both the English pre-nominal adjective order and the French post-nominal adjective order are activated, although the latter to a lesser degree, as it is not the language selected. Sometimes the non-target option can win out, leading to reversal errors, when recent language exposure or practice has strengthened activation of the non-target language. The co-activation account is in line with empirical evidence on crosslinguistic priming in bilingual children (Hsin, Legendre & Omaki, Reference Hsin, Legendre, Omaki, Baiz, Goldman and Hawkes2013), demonstrating that recent exposure to one language can lead to morphosyntactic interference in children's other language, even in the absence of structural overlap. Recently, there have been proposals in the literature to reconceptualise CLI as the outcome of crosslinguistic priming (Hervé, Serratrice & Corley, Reference Hervé, Serratrice and Corley2016; Serratrice, Reference Serratrice2016), as a potential means of providing a unified psycholinguistic approach to explaining different manifestations of CLI across different bilingual populations. The purpose of the present study is to test the predictions of structural overlap and of co-activation, conceptualised within this more recent framework of crosslinguistic priming, in the context of English–French bilingual children's motion event expressions.

2.2 Motion typology: English and French

Although motion is a universally fundamental concept that pervades human experience, its linguistic expression manifests a surprising degree of crosslinguistic variation. Talmy's semantic typology (Reference Talmy and Schopen1985, Reference Talmy2000) is an attempt to systematise this variation by classifying languages according to how the conceptual components of motion event structure are typically mapped onto linguistic devices. In accordance with Talmy (Reference Talmy and Schopen1985, pp. 60–61), motion is defined in this paper as an event involving a figure moving with respect to a ground entity following a certain path. Additionally, motion events may include optional semantic components that constitute co-events, such as the Manner of motion or cause. Talmy distinguishes languages according to where path, the ‘core schema’ of a motion event, is most typically expressed. In so-called verb-framed languages (V-languages), such as French and other Romance languages, path is routinely encoded in the main verb (e.g., monter ‘ascend’), whilst manner is either not verbalised at all or appears in peripheral devices outside the main verb, such as gerundives (e.g., en courant ‘by running’) or adverbials (e.g., à quatre pattes ‘on all fours’). The reverse pattern is found in satellite-framed languages (S-languages), like English and other Germanic languages, where speakers habitually verbalise manner in the main verb and encode path in so-called satellites, i.e., devices outside the main verb, such as particles and prepositional phrases (e.g., into the room).Footnote ¹ These lexicalisation patterns are to be understood as probabilistic tendencies that do not preclude alternative, but more marked ways of expressing motion within a language (e.g., Latinate path verbs in English, such as enter, exit).

With respect to English, the S-framed pattern has indeed been observed to apply very consistently both with respect to basic and more complex motion events (e.g., caused motion). For French and indeed other Romance languages, however, the V-framed classification has proven more problematic. This is due to the availability of several additional lexicalisation options that do not easily fit the V-framed constellation. In French, S-framing is licensed when expressing motion within a location without implying a displacement (e.g., danser dans la maison ‘to dance in the house’). Second, even when describing motion events that do involve displacement, manner-verbs in French can combine with a limited inventory of prepositions that allow path-encoding (e.g., by referring to goals as in jusque ‘towards’). These observations have led to revisions of Talmy's original typology with respect to V-languages. One important refinement concerns the boundary-crossing constraint (Slobin & Hoiting, Reference Slobin and Hoiting1994) according to which path encoding within the verb is obligatory only when a boundary-crossing is involved. In the absence of boundary-crossing, both framing patterns are licensed, resulting in a split framing behaviour that is typical of many V-languages. From the perspective of the bilingual learner, it follows from the above characterisation that there is partial structural overlap between English and French motion encoding. S-framing patterns are available in French, although they are more restricted morphosyntactically, owing to a highly constrained repertoire of path-encoding prepositions, and are excluded entirely only in boundary-crossing situations.

2.3 Motion in bilingual contexts

The majority of research on motion expression in bilinguals has targeted adults: either late L2 learners, or bilingual adults who have acquired both languages in early childhood. Only a few studies have investigated motion expression in bilingual children. Findings for each bilingual acquisition context are reviewed in turn. In adult L2 learning, findings suggest that mapping the target-appropriate semantic component onto the main verb is unproblematic, at least for learners of a V-language. Thus, several studies on L2 learners of Spanish (Cadierno & Ruiz, Reference Cadierno and Ruiz2006; Larrañaga, Treffers-Daller, Tidball & Gil Ortega, Reference Larrañaga, Treffers-Daller, Tidball and Ortega2012; Navarro & Nicoladis, Reference Navarro and Nicoladis2005) report no evidence of L1 transfer of manner verbs, even at intermediate proficiency levels. In contrast, encoding outside the main verb is reported to give rise to persistent transfer in both directions of acquisition: some studies find that L2 learners of V-languages continue to encode path information via partly ungrammatical PPs and particles (Cadierno, Reference Cadierno, Achard and Niemeier2004; Navarro & Nicoladis, Reference Navarro and Nicoladis2005), thus replicating the pattern of their S-framed L1. Conversely, using PPs and particles target-appropriately has been shown to prove challenging for L1 speakers of V-languages who continue to rely on bare verbs in their S-framed L2 (Navarro & Nicoladis, Reference Navarro and Nicoladis2005; Stam, Reference Stam, Han and Cadierno2010), even at advanced proficiency levels. The boundary-crossing constraint constitutes another source of persistent difficulty for L2 learners of V-languages. A range of studies demonstrates that, even at highly advanced levels of proficiency, learners continue to violate the constraint by inaccurately mapping manner onto verbs in combination with anomalous path satellites (e.g., Cadierno & Ruiz, Reference Cadierno and Ruiz2006; Larrañaga et al., Reference Larrañaga, Treffers-Daller, Tidball and Ortega2012).

In the context of adult bilinguals who have acquired both languages in early childhood, the available research suggests unique ‘in-between’ patterns that diverge from the typical tendencies of monolinguals of both languages. For example, bidirectional investigations of motion expression in Spanish–English bilinguals (Filipović, Reference Filipović2011; Hohenstein, Eisenberg & Naigles, Reference Hohenstein, Eisenberg and Naigles2006) have found higher rates of manner verbs in bilinguals’ Spanish relative to monolinguals, but lower rates than in English monolinguals. Similar intermediate encoding tendencies have been observed outside the main verb. In a study on Turkish–German speakers (Daller, Treffers-Daller & Furman, Reference Daller, Treffers-Daller and Furman2011), bilinguals have been reported to use more path satellites than Turkish (V-framed) monolinguals, but fewer than German (S-framed) monolinguals.

In the context of early childhood bilingualism, some of the few available studies report similar in-between encoding tendencies as in adult bilinguals. Thus, in an investigation of Spanish early L2 learners of English in an instructional setting, Aveledo and Athanasopoulos (Reference Aveledo and Athanasopoulos2016) find evidence for L2 influence on the semantics of children's L1 verbs, such that manner is encoded more frequently, but path less so, relative to Spanish monolinguals. Although the study is unidirectional and hence does not test children's encoding preferences in their L2, the authors conclude that their findings suggest a merging process of lexicalisation tendencies of children's two languages. In a bidirectional study of simultaneous English–French bilingual children who acquire both languages naturalistically, Miller, Furman and Nicoladis (Reference Miller, Furman and Nicoladis2018) observe unidirectional CLI such that bilinguals differed from English monolinguals in their more frequent lexicalisation of path (only in token numbers, not in type). Note that Miller et al.'s (Reference Miller, Furman and Nicoladis2018) analysis is based on the overall encoding of path and manner, without distinguishing between verbs and satellites. Our own previous research on the acquisition of caused motion expression in early successive and simultaneous English–French bilingual children (Engemann, Reference Engemann2012, Reference Engemann2016; Harr & Engemann, Reference Harr and Engemann2011) suggested prolific asymmetric CLI in the opposite direction from what was reported in Miller et al. (Reference Miller, Furman and Nicoladis2018). Bilinguals’ French descriptions showed evidence of pervasive influence from English S-framing strategies, whereas English expressions showed little influence from French. Crucially, CLI affected both the verb and peripheral devices. Thus, bilinguals overwhelmingly preferred to use verbs conflating manner and cause (e.g., pousser ‘push’) and resorted to various strategies for expressing path outside the main verb, including some target-deviant PPs and more marginal but formally target-appropriate means, such as gerunds (e.g., en traversant ‘by crossing’).

Summarising, the available research on motion expression in various bilingual contexts suggests an asymmetry in the difficulty of the learner task involved for adult L2 learners of V- vs. S-languages. Specifically, the boundary-crossing constraint and the morphosyntactic restrictions governing peripheral path encoding associated with V-languages appear to be vulnerable to transfer and resistant to restructuring. The evidence for adult bilinguals who acquired both languages in childhood suggests unique bilingual-specific patterns resulting from bidirectional CLI that may potentially indicate convergence in lexicalisation patterns. If this is indeed the case, it raises the question as to when such merging process starts developmentally and underscores the need for more studies on child bilinguals’ motion expression. The scarce evidence available to date on bilingual children is inconclusive and too heterogeneous to allow for meaningful comparisons. It is unclear, for instance, why the two studies on simultaneous English–French bilingual children (Engemann, Reference Engemann2016; Miller et al., Reference Miller, Furman and Nicoladis2018) arrived at different results concerning the directionality of CLI. It is possible that the type of motion event described (complex caused versus simple voluntary motion) and the different outcome measures used play a role. As to the latter, CLI may not become apparent to the same extent if semantic encoding via main verbs and satellites is conflated in the same measure, as was the case in Miller et al. (Reference Miller, Furman and Nicoladis2018). This underscores the need for fine-grained semantic analyses of motion encoding strategies that take into account the potentially differential impact of language-specific morphosyntactic repertoires.

6.1 CLI patterns in motion encoding show evidence for co-activation

This study set out to investigate CLI in child simultaneous bilingual acquisition of English and French in the domain of voluntary motion expression. Two theoretical proposals, the overlap hypothesis (Hulk & Müller, Reference Hulk and Müller2000) and the co-activation account (Nicoladis, Reference Nicoladis2006), the latter reconceptualised within the framework of crosslinguistic priming (Hervé et al., Reference Hervé, Serratrice and Corley2016; Serratrice, Reference Serratrice2016), were put to the test by examining the effects of age and structural overlap (instantiated by the semantic constraint of boundary-crossing) on bilinguals’ and monolinguals’ motion encoding strategies. Different outcomes were predicted for the two proposals in terms of the directionality of CLI, its development as a function of children's age and the occurrence of qualitative target deviations. Children's encoding preferences were analysed in terms of the frequency of packaging semantic information via verbs and peripheral devices, corresponding to the typical S- vs. V-framed strategies.

Before summarising the results, it is important to note that bilinguals’ encoding patterns largely followed the language-specific tendencies of their monolingual peers. Bilinguals’ English descriptions overwhelmingly combined manner verbs with path satellites. In French, bilingual children demonstrated a similar preference as monolinguals for relying on bare verbs encoding path, while making much less use overall of satellites than English speakers. The observation that bilinguals largely adhere to the typological tendencies of each of their languages and thus maintain the contrast between V- and S-framed information distribution principles is an important finding in itself. This shows, firstly, that bilinguals are sensitive to the typological differences characterising motion expression in their two languages from at least as early as four years of age, confirming previous crosslinguistic developmental research in this domain (e.g., Berman & Slobin, Reference Berman and Slobin1994; Hickmann et al., Reference Hickmann, Taranne and Bonnet2009a, Reference Hickmann, Hendriks, Champaud, Guo, Lieven, Ervin-Tripp, Budwig, Özçalişkan and Nakamurab). Secondly, these results demonstrate that bilinguals differentiate their languages in the semantic-conceptual domain, in line with widely attested findings in other linguistic domains, such as morphosyntax (see Serratrice, Reference Serratrice2013).

Notwithstanding the observed parallels, the statistical analyses also revealed a number of important departures from monolingual encoding patterns that support a co-activation account. The key finding in this respect is that, in their English descriptions, bilinguals used significantly more path verbs relative to English monolinguals, while bilinguals tested in French used manner verbs and path satellites more frequently than French monolinguals. In other words, in each of their languages, bilinguals displayed an increased use of the typical framing tendency of their other language, which demonstrates bidirectionality of CLI. Whilst inconsistent with the overlap hypothesis, bidirectional CLI is expected under the co-activation account, which assumes that the prevalent pattern of one language always simultaneously co-activates that of the other language. Given that in the present study, bilinguals’ encoding tendencies in each language were still considerably closer to those of monolinguals of each language than to each other, it would however be misleading to equate the current findings with the ‘in-between’ patterns reported in some previous studies on child and adult bilinguals (Aveledo & Athanasopoulos, Reference Aveledo and Athanasopoulos2016; Filipović, Reference Filipović2011; Hohenstein et al., Reference Hohenstein, Eisenberg and Naigles2006). Nevertheless, the observed general tendency towards a convergence of lexicalisation patterns goes in the same direction documented by previous research on adult bilinguals (e.g., Alferink & Gullberg, Reference Alferink and Gullberg2014; Brown & Gullberg, Reference Brown and Gullberg2013).

The second main finding concerns the effects of condition and age on the occurrence and nature of CLI. Regarding condition (+/- boundary-crossing), bilinguals’ tendency to use S-framing encoding strategies in their French was amplified when describing events involving a boundary-crossing. Moreover, target-deviant motion encodings, such as illicit framing reversals and unacceptable ‘pseudo-PPs’, exclusively occurred in descriptions of boundary-crossings. Given the absence of structural overlap in this condition due to the boundary-crossing constraint (Slobin & Hoiting, Reference Slobin and Hoiting1994), these findings are incompatible with the overlap hypothesis. The results on the effect of age provide further evidence against the overlap account, which would have predicted CLI to diminish with age. Instead, target-deviant path expressions increased significantly between the two tested age groups. Likewise, target-like means of instantiating S-framing (manner verbs and path satellites) did not demonstrate a decrease with age. Both analyses indicate that CLI may be a more persistent phenomenon in bilingual children's production patterns than assumed by the overlap account.

To summarise, having analysed CLI in terms of directionality, age and the role of semantic constraints, the findings presented in this study strongly speak against the overlap account. CLI was shown to occur bidirectionally, to either remain stable or even partly increase with age and to manifest itself mainly in exactly the condition which did not afford structural overlap. In what follows, I propose an explanation of these findings within an extended version of Nicoladis’ co-activation account (Reference Nicoladis2006).

6.2 The dynamics of co-activation during the online speech production process

Even though the co-activation account would predict CLI to occur independently of the presence or absence of structural overlap, it does not explain why CLI should be more prevalent or even exclusive to the condition that did not afford crosslinguistic overlap, i.e., the boundary-crossing condition. In what follows I argue that this is the result of complex interactions between linearisation choices in the conceptualiser and language-specific morphosyntactic restrictions that induce particular crosslinguistic co-activation patterns at the lemma level of speech production. I thereby propose to extend Nicoladis’ account of co-activation by including Levelt's notion of linearisation (Reference Levelt1981, Reference Levelt1989) as a crucial ingredient of speech production that can contribute to explaining the task-dependent dynamics of co-activation.

Given the sequential nature of the speech channel, which requires a linear presentation of one word at a time, Levelt (Reference Levelt1981, pp. 305) states that “the speaker has a linearization problem – that is, a linear order has to be determined over any knowledge structure to be formulated”. Empirical research on speakers’ linearisation strategies suggests that more salient or activated concepts go first in speech production (Ferreira & Rehrig, Reference Ferreira and Rehrig2019; Levelt, Reference Levelt1989). In the present context, the observed prominence of manner verbs in boundary-crossing items, which occurred in all participant groups independently of language background, is likely an artefact of the task in that all the items in this condition portrayed manners that corresponded to activities with a strong leisure character (e.g., ice-skating), which plausibly increased their saliency and hence their activation level to child participants. In terms of linearisation strategies, the increased saliency of manner should give rise to an increase in descriptions that mention manner first, that is, before path. In English, the default lexicalisation pattern already aligns with this strategy, in that manner is typically encoded in the main verb occurring before the PP. That is, the typical sequencing of semantic components in English already fits the increased activation level of the concept of manner in boundary-crossing events. In French, however, where manner is typically either omitted or encoded in the verbal periphery, this increased manner saliency prompted children – both monolinguals and bilinguals – to encode this component in the main verb more frequently than they typically would. In the bilingual children, this tendency was further reinforced relative to monolinguals owing to their simultaneous co-activation of the English pattern, where manner is routinely expressed first.

In the online process of sequencing information, selecting the main verb for manner encoding has problematic consequences for subsequently expressing path in French. This is because, contrary to English, the repertoire of peripheral devices that can unambiguously express a trajectory is extremely restricted in French (see 2.2). Faced with this difficulty, bilinguals resorted to strategies that are either highly idiosyncratic (framing reversals) or outright unacceptable, as in the case of ‘pseudo-satellites’. The fact that even monolingual French children occasionally produced such idiosyncratic expressions might thus reflect the same online linearisation difficulty induced by the situation of high manner saliency, which pushes the French motion system to its typological limits. Although this account is necessarily speculative, such dynamic patterns of crosslinguistic co-activation during the online production process, particularly in response to the linearisation challenge, could account for why qualitative target deviations were observed only in the boundary-crossing condition and only within French, where language-specific restrictions apply that complicate the task of jointly expressing multiple semantic components. Further studies are necessary to address the role of language-specific challenges for linearisation and the impact of conceptual saliency on crosslinguistic co-activation patterns.

6.3 Increase of CLI with age is consistent with co-activation as priming

Although there is some recent evidence of developmental persistence of CLI in simultaneous bilingual acquisition (Bosch & Unsworth, Reference Bosch and Unsworth2020) there is to my knowledge no study reporting an age-related increase of CLI. In the present study, this was exactly what was found in relation to target-deviant satellites in bilingual children's French descriptions. From the perspective of co-activation, it is possible to explain such developmental reinforcement of CLI as a result of children's developing linguistic skills, allowing them to recruit more linguistic resources, that thus become available for co-activation. In the case of the observed target-deviations, children's developing syntactic abilities enabled them to use more complex constructions (such as the French gerundive) to encode path outside the main verb, giving rise to the observed framing reversals. In a similar vein, capitalising on locative prepositions as a means of path encoding presupposes a certain command of the prepositional system and its combinatorial potential with verbs. This line of argument is consistent with experimental evidence on crosslinguistic priming in second language learners showing stronger priming effects in more proficient learners (Bernolet et al., Reference Bernolet, Hartsuiker and Pickering2013; Hartsuiker & Bernolet, Reference Hartsuiker and Bernolet2017). If this explanation is correct, CLI in simultaneous bilingual contexts should not necessarily diminish even in adulthood. Future research would need to ascertain the longevity of CLI from a lifespan perspective by testing adolescent and adult simultaneous bilinguals.

6.4 Implications and open questions

The findings of this study have theoretical implications regarding the role of language-specific semantic constraints for CLI in simultaneous bilingualism. Bilinguals’ violation of the boundary-crossing constraint supports the claim that structures governed by semantic and discourse-pragmatic restrictions are vulnerable to CLI and may result in a weakening or even loss of these constraints in contexts of simultaneous bilingualism (Silva-Corvalán, Reference Silva-Corvalán1994). What remains unclear is the role of structural overlap. Does such weakening of semantic constraints occur only in cases when there is partial overlap with the predominant structure of the other language, where these restrictions do not apply? Alternatively, is it an effect of bilingualism per se for semantic constraints to weaken as part of a general bilingual tendency to maximise crosslinguistically convergent patterns (e.g., Muysken, Reference Muysken2013)? Future research should address this question by systematically comparing the present scenario to the bilingual acquisition of language pairs governed by the same semantic constraint (e.g., two V-languages).

The observation that even in the younger age group (four to six years) bilingual children did not systematically adhere to the boundary-crossing constraint raises further questions about its developmental trajectory. Namely, are we dealing with the gradual weakening of a constraint that had previously been in place, or with a situation of incomplete acquisition? A longitudinal examination of boundary-crossing descriptions in both younger and older bilinguals than those tested in this study would be necessary to address this question. It is possible that bilinguals’ semantic acquisition in this domain manifests a unique pattern from the beginning. If that is so, this raises further questions regarding bilinguals’ event representations of motion and of boundary-crossing displacements in particular. Further studies relying on methods tapping into speakers’ event cognition (such as e.g., eye-tracking, memory and categorisation) will have to ascertain whether the deviations observed on the linguistic level reflect unique bilingual patterns of event representations on a cognitive level.

A striking observation was the fact that even monolingual French children occasionally produced target-deviant ‘pseudo-satellites’ and framing reversals deemed unacceptable by adult monolinguals. In the monolingual group, these deviations cannot be explained as a result of CLI, suggesting the possibility of ongoing processes of language change within French. If this is the case, the French motion system may be undergoing a typological shift towards a system allowing more systematic encoding of path information via satellites. Although necessarily speculative, this suggestion is compatible with recent claims in the literature that bilingual speakers are potential agents of language change (Fernández, De Souza & Carando, Reference Fernández, De Souza and Carando2017; Kootstra & Muysken, Reference Kootstra and Muysken2017; Meisel, Reference Meisel2011b). Alternatively, French may simply be less straightforwardly V-framing than is generally acknowledged, which would lend support to arguments in the literature in favour of classifying French as a mixed or hybrid system (Kopecka, Reference Kopecka, Hickmann and Robert2006; Pourcel & Kopecka, Reference Pourcel and Kopecka2005). Further research is necessary to investigate to what extent the qualitative deviations observed in this study are the temporary result of bilinguals’ overstretching the patterns of a highly variable system of motion encoding, or whether they reflect ongoing language change.

6.5 Limitations

Although the questionnaire administered in this study included parental self-rating measures of children's proficiency in both languages, no independent measures of proficiency, dominance and language exposure were collected in the study. Therefore, we cannot completely rule out the possibility that the occurrence of qualitative CLI in the French sample was due to children being dominant in their English. While acknowledging this possibility, the fact that all bilingual children tested in this study lived in France at the time of testing makes dominance from English less plausible, particularly in light of research suggesting strong effects of the ambient language on bilingual children's motion expression (Daller et al., Reference Daller, Treffers-Daller and Furman2011). If the language of children's environment played a role for the directionality of CLI, we would have expected children's English responses to be affected by their French rather than vice versa.

A second limitation concerns the design of the stimuli in this study. The events portrayed in the boundary-crossing condition conflated several factors: all of the items showed motion on the horizontal axis involving atelic types of manner with a strong leisure character. This makes it impossible to determine whether the strong manner focus observed in this condition is merely an artefact of the task or a more general feature of boundary-crossing events. Note, however, that in a previous study on caused motion expressions in bilingual children (Engemann, Reference Engemann2012) a similar effect of boundary-crossing was observed despite the fact that the manners presented were identical across all conditions and did not correspond to salient leisure activities. The tentative conclusion to draw from this is that there is something about boundary-crossing motion events more generally that induces greater attention to manner and consequently triggers CLI in the context of bilingualism. A promising avenue for future research would be to investigate boundary-crossing events further in different bilingual contexts by manipulating factors such as the degree of telicity involved in the activities shown, the presence of a change of state, and perceptual features such as the type of boundary and the direction of movement (horizontal vs. vertical).