In this study, we examined whether grammatical constructions unique to the second language influence native-language sentence comprehension and the role of individual differences. We obtained acceptability ratings (on a scale of 1-5) for auditorily-presented Spanish sentences that mimic the English causative structure (e.g., *El entrenador corrió a la deportista alrededor de la pista [The trainer ran the athlete around the track]). We hypothesized that bilinguals might be more tolerant of lexical causative structures in Spanish than Spanish monolinguals because the structures are grammatical in English. We compared three groups of highly proficient Spanish-English bilinguals: 15 heritage Spanish bilinguals, 14 early bilinguals, and 12 late bilinguals, and three control groups: two native Spanish-speaking groups with limited English proficiency living in the U.S. (n = 15) and in Ecuador (n = 16), and English monolinguals (listening to English versions) (n = 25).

Early and late bilinguals rated causative sentences as low in acceptability (mean ratings: 2.3 and 2.2, respectively), similar to Spanish controls (2.7 and 2.3), while heritage bilinguals (3.2) were more like English controls (3.7) in judging the sentences to be of higher acceptability. Higher Spanish proficiency was associated with lower acceptability ratings (r = -0.46, p = .002). Causative ratings were higher for participants who reported mostly thinking in English (p = .03) or in both languages (p < .001) compared to those who reported thinking in Spanish. Sentences with higher frequency verbs were rated higher than sentences with lower frequency verbs. Acceptability also increased over the course of the experiment, suggesting further adaptive mechanisms in comprehending and interpreting novel sentences.
In sum, cross-linguistic influence of sentence acceptability was modulated by language proficiency and lexical factors. Our findings reveal that cross-language interactions may change the perceived grammaticality of the native language.