A Model of Early Syntactic Development

A Model of Early Syntactic Development Pat Langley The Robotics Institute Carnegie-Mellon University Pittsburgh, Pennsylvania 1521,3 USA ABSTRACT AMBER is a model of first language acquisition that improves its performance through a process of error recovery. The model is implemented as an adaptive production system that introduces new condition-action rules on the basis of experience. AMBER starts with the ability to say only one word at a time, but adds rules for ordering goals and producing grammatical morphemes, based on comparisons between predicted and observed sentences. The morpheme rules may be overly general and lead to errors of commission; such errors evoke a discrimination process, producing more conservative rules with additional conditions. The system's performance improves gradually, since rules must be relearned many times before they are used. AMBER'S learning mechanisms account for some of the major developments observed in children's early speech. 1. Introduction In this paper, I present a model that attempts to explain the regularities in children's early syntactic development. The model is called AMBER, an acronym for Acquisition Model Based on Error Recovery. As its name implies, AMBER learns language by comparing its own utterances to those of adults and attempting to correct any errors. The model is implemented as an adaptive production system - a formalism well-suited to modeling the incremental nature of human learning. AMEER focuses on issues such as the omission of content words, the occurrence of telegraphic speech, and the order in which function words are mastered. Before considering AMBER in detail, I will first review some major features of child language, and discuss some earlier models of these phenomena. Children do not learn language in an all.or.none fashion. They begin their linguistic careers uttering one word at a time, and slowly evolve through a number of stages, each containing more adult-like speech than the one before. Around the age of one year, the child begins to produce words in isolation, and continues this strategy for some months. At approximately 18 months, the child begins to combine words into meaningful sequences. In order-based languages such as English, the child usually follows the adult order. Initially only pairs of words are produced, but these are followed by three-word and later by four-word utterances. The simple sentences occurring in this stage consist almost entirely of content words, while grammatical morphemes such as tense endings and prepositions are largely absent. During the period from about 24 to 40 months, the child masters the grammatical morphemes which were absent during the previous stage. These "function words" are learned gradually; the time between the initial production of a morpheme and its mastery may be as long as 16 months. Brown (1973) has examined the order in which 14 English morphemes are acquired, finding the order of acquisition to be remarkably consistent across children. In addition, those morphemes with simpler meanings and involved in fewer transformations are learned earlier than more complex ones. These findings place some strong constraints on the learning mechanisms one postulates for morpheme acquisition. …

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