Variability in Verbal Agreement Forms Across Four Signed Languages

In signed languages, agreeing verbs change orientation and/or direction of movement according to targets established by an agreement rule and assigned to locations in signing space. Such verbs do not always match the targets. To determine the nature and source of the mismatches, this study investigated variability in three agreement forms across 70 to 80 verbs in four signed languages. One main finding is that two kinds of constraints determine whether the phonological form of a verb matches the target(s) imposed by the agreement rule: constraints on the degree and on the complexity of articulation. Another finding is that variability was systematic across particular targets for three agreement forms, across all verbs and signed languages. Taken together, the findings suggest that the constraints may be encoded within the phonological system of a sign language. The constraints are further discussed in terms of gestural scores within the framework of Articulatory Phonology: the constraint on degree of articulation is seen as an upper bound on a tract variable, while that on complexity is evaluated in terms of number of phasing relationships. Within the framework of Optimality Theory, which determines optimal output for a given agreement form, ranking of one markedness constraint above a faithfulness constraint determines the output according to degree of articulation, while ranking of a faithfulness constraint over another markedness constraint selects the output according to complexity of articulation.