Studying phonology in sign language
Phonology is the study of the smallest contrastive units of language. These units are the smallest building blocks of language. The building blocks are organized to create words.
Linguists study how the units are organized in a language, how they are combined to form a word, and how they interact with each other.
The smallest units of language in spoken language are called phonemes. In signed language, each sign consists of the five basic parts, called parameters, in which each of the parameters has its set of primes.
Parameters
Each ASL sign (ASL word) consists of all these parameters: handshape, movement, location, palm orientation, and non-manual signals/markers.
Each paramater has a number of primes. For example, the handshape paramater has over 40 different handshapes (handshape primes).
When one of these paramaters (or primes) changes, a signed word results in a different meaning or sometimes meaningless (or "mispronunciation").
Many ASL words have more than one of these parameters in a single production. For example, the ASL word mother+father ("parents") has one handshape, one movement, one palm orientation, and two locations.
References
Clayton Valli, et al. Linguistics of American Sign Language: An Introduction. p 17.