Structural cues for symmetry, asymmetry, and non-symmetry in Central Taurus Sign Language.

We investigate how predicates expressing symmetry, asymmetry and non-symmetry are encoded in a newly emerging sign language, Central Taurus Sign Language (CTSL). We find that predicates involving symmetry (i.e., reciprocal and symmetrical actions) differ from those involving asymmetry (i.e., transitive) in their use of the morphological devices investigated here: body segmentation, mirror-image articulators and double perspective. Symmetrical predicates also differ from non-symmetrical ones (i.e., intransitive) in their use of mirror-image configuration. Furthermore, reciprocal actions are temporally sequenced within a linear structure, whereas symmetrical actions are not. Thus, our data reveal that CTSL expresses each type of action with a particular combination of linguistic devices to encode symmetry, asymmetry, and non-symmetry. Furthermore, differences in the use of these devices across age cohorts of CTSL suggest that some have become more conventionalized over time. The same semantic distinctions have been observed - though with different realization - in another emerging sign language, Nicaraguan Sign Language (NSL). This converging suggests that natural human language learning capacities include an expectation to distinguish symmetry, asymmetry and non-symmetry.