Processes controlling human movement: neuromotor constraints on American Sign Language.

The study of sign languages provides a promising vehicle for investigating language production because the movements of the articulators in sign are directly observable. Movement of the hands and arms is an essential element not only in the lexical structure of American Sign Language (ASL), but most strikingly, in the grammatical structure of ASL: It is in patterned changes of the movement of signs that many grammatical attributes are represented. The "phonological" (formational) structure of movement in ASL surely reflects in part constraints on the channel through which it is conveyed. We evaluate the relation between one neuromotor constraint on movement-regulation of final position rather than of movement amplitude-and the phonological structure of movement in ASL. We combine three-dimensional measurements of ASL movements with linguistic analyses of the distinctiveness and predictability of the final position (location) versus the amplitude (length). We show that final position, not movement amplitude, is distinctive in the language and that a phonological rule in ASL predicts variation in movement amplitude-a development which may reflect a neuromuscular constraint on the articulatory mechanism through which the language is conveyed.