Universal newborn hearing screening provides unprecedented opportunities to identify children with early hearing loss, estimated to affect 1 to 6 per 1,000 newborns in the U.S. today. Children with hearing loss are at chronic risk of underperforming in language and literacy, placing them at considerable risk for academic and learning difficulties. Research has shown that deaf infants exposed to naturally occurring signed languages from birth from deaf signing parents academically outperform deaf individuals who learn sign later in life from non-native hearing parents. Yet, there remains a great need for scientific evidence on early language development in children learning ASL, and no studies have explored the early real-time processing of signed languages by infants and young children using online measures. This project develops the first assessment of efficiency in language interpretation by infants and toddlers learning ASL, through a novel adaptation of the looking-while-listening (LWL) procedure developed by Fernald et al., (1998; 2008). Over the last decade, the Fernald group has explored how young hearing children develop crucial processing skills as they learn to listen for meaning in spoken language, discovering significant individual differences in processing efficiency that strongly predict later language outcomes. In extending this research to children learning ASL, we build on these extensive previous studies with monolingual and bilingual children learning spoken languages, as well as on pioneering studies from the Corina lab on ASL processing by deaf adults. Participants include two groups of 18-36 mo-old children learning ASL: (a) deaf children of deaf parents (deaf-of-deaf - DODs, n=25) and (b) hearing children of deaf parents (children of deaf adults - CODAs, n=25). CODAs will also have various amounts of exposure to spoken English. We also include a third comparison group of (c) hearing children learning only English (n=25). To assess real-time language processing efficiency, DOD and CODA participants will be tested in the LWL-ASL task adapted for use with sign stimuli; CODA children and hearing children learning only English will be tested on a comparable procedure using spoken English-language stimuli. Both tasks assess children's speed and accuracy in interpreting familiar signs/words, and also their skill at using knowledge of familiar signs/words to learn novel signs/words. Sign/word vocabulary will be assessed offline with parent report and face-to-face instruments. A sub-set of the children will be re-tested 6 months later. The proposed research will be the first study of the consequences of individual differences in early real-time sign comprehension in native learners of ASL, providing the opportunity to explore the role of variation in language exposure in sign processing efficiency in both deaf and hearing sign-exposed infants. This exploratory study will also lead to the development of potentially valuable new measures for use in future assessments of children who vary in types of sign language exposure, providing benchmarks for clinicians and caregivers who need to chart linguistic competencies in deaf children receiving early interventions.