Abstract: Common features in sign languages that have no history of contact present a puzzle. The current article brings together findings from three studies of Lengua de Señas Nicaragüense (LSN) to identify processes that underpin the inception and changes in language as it emerges. We use an apparent time approach to capture language change in three domains: pointing and deixis, nonmanual markers with Wh-questions, and spatial differentiation for locatives and arguments. By comparing the language of Nicaraguan homesigners, three successive cohorts of LSN signers, and the signing of hearing children of deaf LSN signers (Codas), we propose that language change is characterized by two complementary processes, in balance: emergence and convergence. Emergence is the constructive process by which forms arise, such as new lexical items, new patterns of word order, and new mappings between forms and functions, such as a pointing sign taking on a pronominal function (study 1). We argue that vertical transmission from a more experienced user to a less experienced learner drives emergence, often via linguistic reanalysis in which the learner assigns a different function to a form than the one used in the grammar of the experienced user. Complementing the process of emergence, convergence is the reductive process by which competing forms and structures are condensed to a smaller set to achieve parity across a group of language users, a process exemplified by the selection of the brow furrow and head tilt to accompany Wh-questions (study 2). We argue that horizontal peer interactions are key to convergence processes; the language of learners who do not experience such peer interactions, such as homesigners and Codas, shows less convergence (study 3). Taken together, these studies illustrate how the developmental characteristics of the learner intersect with the characteristics of their language (internal ecology), environments, and interactions (external ecology) to drive the processes of language change. We conclude that both vertical transmission and horizontal peer interactions are key to the emergence of new languages, enabling the mechanisms responsible for the typological similarities observed across unrelated languages.
Coppola et al. (Mon,) studied this question.