This thesis investigates the importance of nonmanual signals (facial expressions, movements of the head and body) in American Sign Language (ASL), and argues that nonmanual signals are the overt realization of logical operators. First, we explore the effect of English influence on nonmanual signals, using Kidd’s (2010) theory of the displacement of elements. Second, we examine native signers’ interpretation of a nonmanual coordinator that is ambiguous between inclusive-disjunction/conjunction, and may be disambiguated with additional nonmanual signals (Davidson, 2013). We find a mismatch between linguistic competence and linguistic performance in delayed first language learners, and a preference for a conjunctive interpretation by native signers when there is a lack of disambiguating cues. We show that this preference is part of a general pattern in populations with the inclusive-disjunction/conjunction ambiguity, such as adult speakers of Warlpiri (Bowler, 2014) and English-speaking children (Singh et al., 2013).