Co-evolution of Language and of the Language Acquisition Device

A new account of parameter setting during grammatical acquisition is presented in terms of Generalized Categorial Grammar embedded in a default inheritance hierarchy , providing a natural partial ordering on the setting of parameters. Experiments show that several experimentally effective learners can be defined in this framework. Ew)lutionary simulations suggest that a lea.rner with default initial settings for parameters will emerge, provided that learning is memory limited and the environment of linguistic adaptation contains an appropriate language. 1 Theoretical Background Grmnnmtical acquisition proceeds on the basis of a partial genotypic specifica.tion of (universal) grmn-mar (UG) complemented with a learning procedure elmbling the child to complete this specification appropriately. The parameter setting frainework of Chomsky (1981) claims that learning involves fixing the wdues of a finite set of finite-valued parameters to select a single fully-specified grammar from within the space defined by the genotypic specification of UG. Formal accounts of parameter setting have been developed for small fragments but even in these search spaces contain local maxima and subset-superset relations which may cause a learner to converge to an incorrect grammar The solution to these problems involves defining d(,fault, umnarked initial values for (some) parameters and/or ordering the setting of paraineters during learning. Bickerton (1984) argues for the Bioprograin Hypothesis a.s an explanation for universal similarities between historically unrelated creoles, and for the rapid increase in gramlnatical complexity accompanying the transition from pidgin to creole languages. Prom the perspective of the parameters framework, the Bioprogram Hypothesis claims that children are endowed genetically with a UG which, by default, specifies the stereotypical core creole grammar, with right-branching syntax and subject-verb-object order , as in Saramaccan. Others working within the parameters framework have proposed unmarked, default parameters (e.g. Lightfoot, 1991), but the Bio-program Hypothesis can be interpreted as towards one end of a continuum of proposals ranging from all parameters initially unset to all set to default values. A model of the Language Acquisition Device (LAD) incorporates a UG with associated parameters, a parser, and an algorithm for updating initial parameter settings on parse failure during learning. Basic categorial grammar (CG) uses one rule of application which combines a functor category (containing a slash) with an argument category to form a derived category (with one less slashed argument category). Grammatical constraints of order and agreement are captured by only allowing directed application to adjacent matching categories. Generalized Categorial Grammar (GCG) extends CG with …