Department of Psychology, Barnard College
as1038@columbia.edu

abstract

Early in life, children are more adept at learning language than they will be as adults. This ability is often ascribed to biologically-endowed language-learning capacities available only during an early sensitive period. Such a period would presumably have evolved to be of sufficient duration to enable children to acquire language efficiently in a normal social environment that includes a fully-developed natural language.

In such an environment the grammar acquired closely resembles that of the input language. In those rare situations in which a child's linguistic environment is impoverished, the language-learning capacities are confronted with a more demanding task. Here, it might be expected that the impoverished input would be augmented by the child's capacities to produce a richer output. However, no such child has generated a full language. Perhaps the time required to generate one exceeds the individual's sensitive period. If so, sequential cohorts of child learners might eventually converge on a fully-developed language.

The recent emergence of Nicaraguan Sign Language enables us to consider such a case. The cohort of deaf Nicaraguans entering school in the late 1970s began developing the first community-wide sign language known in Nicaragua. A second cohort of children, entering school ten years later, learned this system from their older peers. Augmentation of the language at that time is still evident in differences between the two cohorts today.

One difference between the cohorts is evident in their expression of semantic roles (Senghas, et al., 1997). The first cohort consistently uses a simple, systematic word order that effectively makes the agent/patient distinction. The second cohort has modified this system, often producing sentences in which semantic roles are no longer unambiguously derivable from the word order. However, certain spatial constructions may be emerging to fill the gap morphologically. In both production (Senghas et al., 1997) and comprehension (Senghas, 1999), the side to which a sign is produced was found to be a meaningful, contrastive feature for second-cohort signers only. This change means that in cases where the context provides minimal cues, second-cohort signers actually misinterpret the assignment of semantic roles in the sentences produced by first-cohort signers. Thus, the second cohort has reanalyzed spatial contrasts to form a stricter, narrower system in which certain referents are specified more precisely.

Additionally, these spatial mappings do not appear to be derived directly from those used to describe the physical locations of objects. The sign-space to physical-space mappings used by even the second cohort in locative descriptions is much more variable than that used for semantic roles. Only in the case of semantic roles has the younger cohort converged on a shared construction community-wide.

These findings indicate that Nicaraguan Sign Language has undergone significant grammatical developments as it has acquired a second cohort of native signers. Some of these changes, such as the rules concerning common word orders, involve a broadening, in which new constructions are allowed. Others, such as the emergence of spatial devices, involve increasing specificity. Because both kinds of processes play a role in language learning and language change, both are now evident in language genesis.

 Conference site: http://www.infres.enst.fr/confs/evolang/