Abstract Language Acquisition in the Absence of Explicit Negative Evidence How Important is.pdf

Language Acquisition in the Absence of Explicit Negative Evidence: How Important is Starting Small? Douglas L. T. Rohde David C. Plaut Carnegie Mellon University and the Center for the Neural Basis of Cognition June 1999 To appear in Cognition Abstract It is commonly assumed that innate linguistic constraints are necessary to learn a natural language, based on the apparent lack of explicit negative evidence provided to children and on Gold’s proof that, under assumptions of virtually arbitrary positive pre- sentation, most interesting classes of languages are not learn- able. However, Gold’s results do not apply under the rather com- mon assumption that language presentation may be modeled as a stochastic process. Indeed, Elman (1993, Cognition) demon- strated that a simple recurrent connectionist network could learn an artificial grammar with some of the complexities of English, including embedded clauses, based on performing a word pre- diction task within a stochastic environment. However, the net- work was successful only when either embedded sentences were initially withheld and only later introduced gradually, or when the network itself was given initially limited memory which only gradually improved. This finding has been taken as support for Newport’s “less is more” proposal, that child language acqui- sition may be aided rather than hindered by limited cognitive resources. The current article reports on connectionist simula- tions which indicate, to the contrary, that starting with simpli- fied inputs or limited memory is not necessary in training recur- rent networks to learn pseudo-natural languages; in fact, such restrictions hinder acquisition as the languages are made more English-like by the introduction of semantic as well as syntac- tic constraints. We suggest that, under a statistical model of the language environment, Gold’s theorem and the possible lack of explicit negative evidence do not implicate innate, linguistic- specific mechanisms. Furthe