Three studies are presented in this paper that address how nonsigners perceive the visual prosodic cues in a sign language. In Study 1, adult American nonsigners and users of American Sign Language (ASL) were compared on their sensitivity to the visual cues in ASL Intonational Phrases. In Study 2, hearing, nonsigning American infants were tested using the same stimuli used in Study 1 to see whether maturity, exposure to gesture, or exposure to sign language is necessary to demonstrate this type of sensitivity. Study 3 addresses nonsigners' and signers' strategies for segmenting Prosodic Words in a sign language. Adult participants from six language groups (3 spoken languages and 3 sign languages) were tested. The results of these three studies indicate that nonsigners have a high degree of sensitivity to sign language prosodic cues at the Intonational Phrase level and the Prosodic Word level; these are attributed to modality or "channel" effects of the visual signal. There are also some differences between signers' and nonsigners' sensitivity; these differences are attributed to language experience or language-particular constraints. This work is useful in understanding the gestural competence of nonsigners and the ways in which this type of competence may contribute to the grammaticalization of these properties in a sign language. (Contains 11 tables, 4 figures and 8 notes.)