Consistency of Sign Language Movement Expression among Proficient and Student Signers

While movement variability is a natural element of human expression, in sign languages it may affect mutual understanding, learning, and potential overuse injury. Sign language variability is not well-understood in part because quantitative analytical methods are yet to be clearly defined. Hence the aim of this study was to assess intra-subject reliability across repeated sessions for three signers, to identify features sensitive to experience-related differences in motor control consistency, and to establish movement consistency metrics for treating sign language kinematic differences as linguistically meaningful. Three signers were assigned to three different proficiency levels of sign language: Deaf (D), proficient (P), and student (S). Sign production variables were evaluated using intraclass correlation coefficients (ICCs) and coefficients of variation(CVs).Most kinematic features showed good to excellent ICCs such as duration, path length, signing space volume, and average and peak velocity. Some EMG features such as mean forearm amplitudes and co-contraction also showed good to excellent ICCs. These data can be used to improve the scientific investigation of sign languages, improve educational resources, and establish baseline thresholds to inform ergonomic or scheduling guidelines for interpreters.