Heritage language in a border-shift context: Differential input effects on sentence comprehension

Abstract This study examines sentence comprehension in two in-situ heritage Slovene communities in Italy’s border-shift context, comparing the Gorizia/Trieste (N = 66) and Natisone Valley (N = 43) adult populations with monolingual Slovene speakers. While both heritage groups operate in Italian-dominant bilingual environments near the Slovenian border, they differ in Slovene exposure due to varying institutional support. Using a sentence–picture verification task, this study examines comprehension of non-canonical word order, relative clauses and cataphoric dependencies. The Gorizia/Trieste group performed comparably to monolinguals, demonstrating strong sensitivity to case morphology and syntactic processing. Conversely, the Natisone group showed reduced accuracy and longer response times across all domains, reflecting case system vulnerability and processing limitations linked to reduced exposure. These findings highlight the important role of active maintenance and institutional support, independent of geographical proximity to the mainland, in shaping heritage language grammars and their use.