Defaulting effects contribute to the simulation of cross-linguistic differences in Optional Infinitive errors

This paper describes an extension to the MOSAIC model which aims to increase MOSAIC’s fit to the cross-linguistic occurrence of Optional Infinitive (OI) errors. While previous versions of MOSAIC have successfully simulated these errors as truncated compound finites with missing modals or auxiliaries, they have tended to underestimate the rate of OI errors in (some) obligatory subject languages. Here, we explore defaulting effects, where the most frequent form of a given verb is substituted for less frequent forms, as an additional source of OI errors. It is shown that defaulting in English tends to result in the production of bare forms that are indistinguishable from the infinitive, while defaulting in Spanish is less pronounced, and tends to result in the production of 3 person singular forms. Dutch verb forms are dominated by the stem in corpus-wide statistics, and the infinitive in utterance-final position, suggesting defaulting in Dutch may change qualitatively across development. Defaulting is shown to increase MOSAIC’s fit to English and Dutch without affecting its already good fit to Spanish, and provides a potential way of simulating the cross-linguistic pattern of verb-marking errors in children with SLI.