A key challenge when learning language in naturalistic circumstances is to extract linguistic information from a continuous stream of speech. This study investigates the predictors of such implicit learning among adults exposed to a new language in a new modality (a sign language). Sign-naïve participants (N = 93; British English speakers) were shown a 4-min weather forecast in Swedish Sign Language. Subsequently, we tested their ability to recognise 22 target sign forms that had been viewed in the forecast, amongst 44 distractor signs that had not been viewed. The target items differed in their occurrence frequency in the forecast and in their degree of iconicity. The results revealed that both frequency and iconicity facilitated recognition of target signs cumulatively. The adult mechanism for language learning thus operates similarly on sign and spoken languages as regards frequency, but also exploits modality-salient properties, for example iconicity for sign languages. Individual differences in cognitive skills and language learning background did not predict recognition. The properties of the input thus influenced adults’ language learning abilities at first exposure more than individual differences.

We investigated whether sign‐naïve learners can infer and learn the meaning of signs after minimal exposure to continuous, naturalistic input in the form of a weather forecast in Swedish Sign Language. Participants were L1‐English adults. Two experimental groups watched the forecast once (n = 40) or twice (n = 42); a control group did not (n = 42). Participants were then asked to assign meaning to 22 target signs. We explored predictors of meaning assignment with respect to item occurrence frequency and three facets of visual motivation: iconicity, transparency, and gesture similarity. Meaning assignment was enhanced by exposure and item frequency, thereby providing evidence for implicit language learning in a new modality, even under challenging naturalistic conditions. Accuracy was also contingent upon iconicity and transparency, but not upon gesture similarity. Meaning assignment at first exposure is thus visually motivated, although the overall low accuracy rates and further qualitative analyses suggest that visually motivated meaning assignment is not always successful.

A key challenge when learning language in naturalistic circumstances is to extract linguistic information from a continuous stream of speech. This study investigates the predictors of such implicit learning amongst adults exposed to a new language in a new modality. Sign-naïve participants (N=93; British-English speakers) were shown a 4-minute weather forecast in Swedish Sign Language. Subsequently, we tested their ability to recognise 22 target sign forms. The target items differed in their occurrence frequency in the forecast, and in their degree of iconicity. The results revealed that both frequency and iconicity facilitated recognition cumulatively. The adult mechanism for language learning thus operates similarly on sign and spoken languages as regards frequency, but also exploits modality-salient properties, e.g., iconicity for sign languages. Individual differences in cognitive skills did not predict recognition. The properties of the input thus influenced adults’ language learning abilities at first exposure more than individual differences.