Repetition Preferences in Two-Handed Balanced Signs: Vestigial Locomotor Central Pattern Generators Shape Sign Language Phonetics and Phonology

Abstract

Language is produced by bodies that evolved to fulfill a variety of functions, most of them non-communicative. Vestigial influences of adaptation for quadrupedal locomotion are still affecting bimanual actions, and have consequences on manual communication systems such as sign languages of the deaf. We discuss how central pattern generators (CPGs), networks of nerve cells in the spinal cord that drive locomotion, influence bimanual actions with alternating movements to be produced with repeated motion. We demonstrate this influence with data from three unrelated sign languages, American Sign Language, British Sign Language, and Hong Kong Sign Language: in all three sign languages two-handed balanced signs produced with alternating movements have a tendency to be repeated, whereas other types of two-handed balanced signs show the opposite tendency for single movements. These tendencies cannot be fully explained by factors such as iconicity. We propose a motoric account for these results: as alternating bimanual movements are influenced by locomotor patterns, they favor repeated movements.

A Vexing Question in Motor Control: The Degrees of Freedom Problem

“…Although it is generally assumed that CPGs, typically located in the spinal cord and brain stem, are characterized by the ability to operate with a minimal intervention of higher brain areas, still they require modulatory inputs in order to perform in a flexible way. The role of CPGs in less stereotyped motor behaviors, characterized by a clear cognitive interaction, has been clarified in the field of speech motor control ( Barlow et al, 2010 ; Rusaw, 2013 ) or sign language ( Tkachman et al, 2021 ). Reaching movements seem to be far away from the area of motor control related to rhythmicity related to CPGs.…”

Simultaneous structures in sign languages: Acquisition and emergence

“… 4 Tkachman et al (2021) report an analysis of dictionary data from ASL, British Sign Language (BSL), and Hong Kong Sign Language (HKSL); they found that two-handed symmetrical signs with alternating (out-of-phase) movement are typically repeated (unlike two-handed signs in which the two hands move in phase). They ascribe this result to central pattern generators involved in locomotion.…”