Unifying Cross-linguistic and Within-language Patterns of Finiteness Marking in MOSAIC

Unifying Cross-linguistic and Within-language Patterns of Finiteness Marking in MOSAIC Daniel Freudenthal (D.Freudenthal@liv.ac.uk) Julian Pine (Julian.Pine@liv.ac.uk) School of Psychology, University of Liverpool Fernand Gobet (Fernand.Gobet@Brunel.ac.uk) School of Social Sciences and Law, Brunel University age, but optionally under-specify Agreement and/or Tense. Due to cross-linguistic differences between the grammars of pro-drop and obligatory subject languages, this leads to the provision of non-finite verb forms in contexts where a finite verb form is required in obligatory subject languages such as English and Dutch, but not in pro-drop languages such as Spanish. The great strength of Wexler’s account, which is consistent with the Universal Grammar approach to language acquisition (Chomsky, 1981; Pinker, 1984) is that it provides a unified explanation of the cross-linguistic occurrence of Optional Infinitive errors. Recently, however, Freudenthal, Pine and Gobet (2006, submitted) have shown that the cross-linguistic differences in the occurrence of Optional Infinitive errors may reflect sensitivity to differences in the distributional statistics of the input children are subject to. Thus, Freudenthal et al. showed that MOSAIC, a performance limited distributional analyser which receives child-directed speech as input and learns to produce progressively longer utterance-final phrases provides a good fit to the developmental characteristics of the Optional Infinitive phenomenon in English, Dutch, German and Spanish. The key to MOSAIC’s simulation of the differential rates of Optional Infinitive errors across the four languages is its bias towards learning material that occurs near the end of an utterance. Since finite and non- finite verbs pattern differently in the four languages, utterance-final phrases have radically different proportions of non-finite verbs. MOSAIC was therefore able to provide a good quantitative fit to the cross-linguistic data as a result of the interaction between its utterance-final bias and the distributional properties of the languages to which it was exposed. While MOSAIC’s ability to deal with the cross-linguistic pattern of finiteness marking based on one, relatively simple processing constraint is encouraging, a clear challenge for MOSAIC remains the simulation of the pattern of regularities in finiteness marking that has been found within languages that display the OI phenomenon. Thus, Poeppel and Wexler (1993) have identified a number of constraints relating to verb placement, differential rates of OI-errors in declaratives and Wh-questions, and the correlation between the provision of subjects and the finiteness of an utterance. These regularities, which are particularly noticeable in Abstract MOSAIC, a model that has already simulated cross-linguistic differences in the occurrence of the Optional Infinitive phenomenon, is applied to the simulation of the pattern of finiteness marking within Dutch. This within-language pattern, which includes verb placement, low rates of Optional Infinitives in Wh-questions and the correlation between finiteness marking and subject provision, has been taken as evidence for the view that children have correctly set the clause structure and inflectional parameters for their language. MOSAIC, which employs no built-in linguistic knowledge, clearly simulates the pattern of results as a function of its utterance-final bias, the same mechanism that is responsible for its successful simulation of the cross- linguistic data. These results suggest that both the cross- linguistic and within–language pattern of finiteness marking can be understood in terms of the interaction between a simple resource-limited learning mechanism and the distributional statistics of the input to which it is exposed. Thus, these phenomena do not provide any evidence for abstract or innate knowledge on the part of the child. The Optional Infinitive phenomenon One of the key features of children’s early multi-word speech is that, in many languages, children often produce utterances that contain non-finite verb forms in contexts where a finite verb form is obligatory in the adult language. Thus, English-speaking children may produce utterances such as he go instead of he goes. While the English example may suggest that the child has simply omitted the inflectional morpheme (-es), data from languages such as German and Dutch where the infinitive carries its own morphological marker (-en) make it clear that children actually produce an infinitive instead of a finite verb form. Thus, German-speaking children may produce utterances such as Vater spielen (Daddy play-inf) instead of Vater spielt (Daddy plays-fin). While such Optional Infinitive errors are quite frequent in obligatory subject languages such as English, Dutch and German, they are quite rare in pro-drop languages like Spanish and Italian. An influential theory by Wexler (1994, 1998) explains this cross-linguistic pattern of results (and the relative sparseness of other types of errors) by assuming that children have correctly set all the clause structure and inflectional parameters for their language from a very early