Learners' ability to recognize linguistic contrasts in American Sign Language (ASL) was investigated using a paired-comparison discrimination task. Minimal pairs containing contrasts in five linguistic categories (i.e., the formational parameters of movement, handshape, orientation, and location in ASL phonology, and a category comprised of contrasts in complex morphology) were presented in sentence contexts to a sample of 127 hearing learners at beginning and intermediate levels of proficiency and 10 Deaf native signers. Participants' responses were analyzed to determine the relative difficulty of the linguistic categories and the effect of proficiency level on performance. The results indicated that movement contrasts were the most difficult and location contrasts the easiest, with the other categories of stimuli of intermediate difficulty. These findings have implications for language learning in situations in which the first language is a spoken language and the second language (L2) is a signed language. In such situations, the construct of language transfer does not apply to the acquisition of L2 phonology because of fundamental differences between the phonological systems of signed and spoken languages, which are associated with differences between the modalities of speech and sign.