New insights into nineteenth-century ASL.

The study of language change in American Sign Language (ASL) has been constrained by a limited historical record. Here we present five case studies that demonstrate how applying a broad set of historical methods, together with the consultation of underutilized sources of sign data, can shed new light on ASL in the 19th century. These case studies cover aspects of two subsystems of ASL, (i) the fingerspelling alphabet and (ii) the numeral system, as well as (iii) the etymologies of selected initialized signs, (iv) the innovation of superordinate terms, and (v) phonological variation in the mano cornuta, or horns, handshape. We argue that these case studies reveal two broad drivers of change in the history of ASL. Bottom-up changes, often driven by biomechanical or perceptual factors, originated within the ASL signing community, likely without signers' conscious awareness. Top-down, or prescriptive, changes were effective in the early years of ASL, when the signing community was small and still tightly linked to schools for the deaf where these changes were instituted and where they first spread. [ABSTRACT FROM AUTHOR]