Naive English-speaking learners' use of indirect positive evidence

When second language learners are faced with acquiring a grammar that is a subset of their native language grammar, direct positive evidence is unavailable. We question whether learners can instead use indirect positive evidence: evidence drawn from errors in the learner's L1 made by native speakers of the learner's L2. We examine if naive English-speaking learners of Mandarin can determine from plural omission errors in Mandarin speakers' English productions that Mandarin marks plural in a subset of conditions under which English does. Participants were exposed to indirect positive evidence via an English-medium dialogue where a native Mandarin-speaking interlocutor produced all contextually plural nouns as singulars. Subsequently, participants learnt 12 Mandarin-like nouns in singular contexts, after which their word learning was tested using both singular and plural pictures as prompts. Forty percent of participants correctly deduced that strings to which they had assigned singular interpretations were also appropriate in plural contexts. Follow-up questions revealed that they noticed the errors in the dialogue and used these to inform their understanding of plural marking in Mandarin. This result suggests that indirect positive evidence may be an effective tool for real language learners to acquire a grammar that is a subset of their native grammar.