Cyclic movement primitives underlying two-handed alternating signs in signed language

Abstract

Biomechanical constraints have been described as underlying patterns in speech production: e.g., cyclic neural central pattern generators (CPGs) in the jaw that evolved for chewing have been claimed to affect syllabic patterns [MacNeilage 1998, Behav. Brain Sci. 21: 4] and cyclic patterns in tongue tip movement may span sequences of segments [Derrick & al. 2015, JASA-EL 137:3]. Similarly, we propose that otherwise unexplained universal aspects of sign languages may result from a preference for repeated alternating arm movements developed in human ancestors for quadrupedal locomotion. For example, in ASL-LEX corpus of 1000 ASL signs, 159 are balanced (not including signs without movement or articulated in the transverse plane, which has alternative properties we will address in the talk). Of those, 60% are alternating, and the alternating group had fewer iconic signs (30.5% vs 41%) and more repeated signs (61% vs 30%) than symmetrical signs. While both groups had a large proportion of signs realized on coronal plane, which makes them more visible in face-to-face communication (33% for alternating vs 52% for symmetrical), the former have more signs in midsagittal and coronal/transverse planes (63% vs 44%), as predicted. Supporting data from additional sign languages will be presented.