Rules or Associations in the Acquisition of Morphology? The Frequency by Regularity Interaction in Human and PDP Learning of Morphosyntax

Abstract

When fluent English speakers are asked to produce past tense forms, their latencies are affected by frequency of past tense forms when generating irregular inflections, but not when generating regular ones. This interaction has been used to support hybrid accounts of morphosyntax where regular inflections are computed by an affixation rule in a neurally based symbol manipulating syntactic system, while irregular verbs are retrieved from an associative memory. This article describes adult learning of morphosyntax in a novel language where frequency and regularity are factorially combined. The accuracy and latency data demonstrate frequency effects for both regular and irregular forms early in the acquisition process. However, as learning progresses, the frequency effect on regular items diminishes whereas it remains for irregular items. The regularity by frequency interaction is a natural consequence of the power law of practice and is thus entirely consistent with associative learning processes: Regularity is frequency by another name. Performance of a simple connectionist system, when trained on the same materials, shows a very close correspondence to the human acquisition data.