Adult heritage speakers of Spanish in the US and subject placement in presentational unaccusative sentences: How are their grammars constrained?

• Spanish Verb-Subject order in sentence focus unaccusatives is locative inversion. • Heritage speakers rely on explicit stage topic for sentence focus unaccusative VS. • Heritage speakers rely on long subject for sentence focus unaccusative VS. • Bilingual processing costs underly word-order variability in heritage Spanish. • Cross-linguistic influence doesn't drive word-order variability in heritage Spanish. Adult heritage speakers (HSs) of Spanish show Subject-Verb (SV)/Verb-Subject (VS) word-order variation in unaccusative sentences marking sentence focus, while monolingual speakers favor VS, as in Llegó Sara 'Sara arrived'. Yet, few empirical studies have explored the distributional rates and patterns associated with this word-order variation in perception and production among HSs. We examine the variable-rule system underlying HSs' acceptability judgments and written-narrative production to articulate how their choices between SV and VS are constrained. We begin with an alternative argument to the Unaccusativity Hypothesis, that unaccusatives instantiating sentence focus are instances of locative inversion where the preverbal position is occupied by an explicit or silent spatiotemporal argument (stage topic) licensing VS order. The results of two context-rich, novel experiments revealed two properties that contributed to HSs' use of VS order: an explicit stage topic and a subject longer than four words. If these were not realized, HSs became increasingly inclined towards SV order. Assuming that interpreting a silent stage topic or a short subject taxes the cognitive resources required to retrieve the relevant discourse-pragmatic information, our findings support recent acquisition theories that attribute HSs' divergent patterns to processing costs rather than the traditional view based on cross-linguistic influence. [ABSTRACT FROM AUTHOR]