Intergenerational influence and ontogenetic development in the emergence of spatial grammar in Nicaraguan Sign Language

The recent emergence of a new sign language among deaf children and adolescents in Nicaragua provides an opportunity to study how grammatical features of a language arise and spread, and how new language environments are constructed. The grammatical regularities that underlie language use reside largely outside the domain of explicit awareness. Nevertheless, knowledge of these regularities must be transmitted from one generation to the next to survive as part of the language. During this transmission, language form and use is shaped by both the characteristics of ontogenetic development within individual users and by historical changes in patterns of interaction between users. To capture this process, the present study follows the emergence of spatial modulations in Nicaraguan Sign Language (NSL). A comprehension task examining interpretations of spatially modulated verbs reveals that new form-function mappings arise among children who functionally differentiate previously equivalent forms. The new mappings are then acquired by their age peers (who are also children), and by subsequent generations of children who learn the language, but not by adult contemporaries. As a result, language emergence is characterized by a convergence on form within each age cohort, and a mismatch in form from one age cohort to the cohort that follows. In this way, each age cohort, in sequence, transforms the language environment for the next, enabling each new cohort of learners to develop further than its predecessors.