The segmental phonology of sign language is currently modeled with feature geometry and dependency relations. These models typically assume three phonemic classes as primitives (handshape, place of articulation and movement), and derive a fourth, orientation, as a result of the interaction between handshape and place of articulation. Current sign language models approach orientation as a relation between a hand-part and a plane of articulation. This relative way of defining it allows getting rid of the reference to the body as a landmark.
The goals of this study are i) to provide evidence for the need of absolute orientation in addition to relative orientation in order to capture the phonology of some signs, and ii) to minimally enrich current models which are only based on relative orientation so that the phonology of these “exceptional” signs is also accounted for.
We use French sign language symmetrical two-handed signs produced on the body like BELT, BONE, TABOO, UNEMPLOYMENT as a case study. We show that relative orientation does not meet descriptive adequacy when the two hands contact each other. Relative orientation can either capture the contact between the hands or the contact with the body, but not both. We propose secondary planes as a formal step to model orientation for these signs. While the implementation of this solution requires minimal changes in current theories, the impact on the whole theory of segmental phonology for sign is quite important. The core conceptualization of orientation as a purely relational phonemic class does not hold anymore (at least not for these signs), as secondary planes impose geometrical restrictions that force absolute orientation.