The non-linguistic status of the Symmetry Condition in signed languages

Since Battison (1978), it has been noted in many signed languages that the Symmetry Condition constrains the form of two-handed signs in which two hands move independently. The Condition states that the form features (e.g., the handshapes and movements) of the two hands are ‘symmetrical’. The Symmetry Condition has been regarded in the literature as a part of signed language phonology. In this study, we examine the linguistic status of the Symmetry Condition by comparing the degree of symmetry in signs from Sign Language of the Netherlands and speech-accompanying representational gestures produced by Dutch speakers. Like signed language, such gestures use hand movements to express concepts, but they do not constitute a linguistic system in their own right. We found that the Symmetry Condition holds equally well for signs and spontaneous gestures. This indicates that this condition is a general cognitive constraint, rather than a constraint specific to language. We suggest that the Symmetry Condition is a manifestation of the mind having one active ‘mental articulator’ when expressing a concept with hand movements.