Joanisse, M. F. ¹ & Bryant, K. J. ^{1, 2}

1 The University of Western Ontario
2 University of Toronto - Ontario Institute for Studies in Education

Theories of inflectional morphology differ with respect to how they predict lexical variables will influence processing of regular and irregular forms. In this study we revisit the well-known case of past tense verbs in English with an eye to better understanding the relative contributions of frequency, regularity, and consistency (i.e., similarity of transformation among inflected forms). In Experiment 1, adult English speakers (N=54) viewed a present tense verb on-screen and named its past tense as quickly as possible. We obtained data for both regular and irregular verbs, across a range of frequencies and consistencies. The results yielded several interesting patterns. Both regular and irregular verbs showed frequency effects marked by slower generation of lower frequency items. Additionally, we observed slower RTs for inconsistent regulars than consistent regulars, although irregulars showed no apparent consistency effect. The overall findings contradict the view that regular inflections are produced by a rule mechanism that is insensitive to lexical variables. However the lack of a consistency effect in irregulars might also be problematic for a single-mechanism theory in which all past tenses are processed within a single system able to code phonological similarity among forms. In Experiment 2 we examined this more closely by presenting the same items to a connectionist model of past tense (Joanisse & Seidenberg, 1999; Woollams, Joanisse & Patterson, 2009). Model responses showed a striking similarity to human RTs, both with respect to the effects of frequency and consistency. We suggest that a single mechanism encodes both regular and irregular patterns, but in a way that optimizes the types of statistical regularities that are useful for subsequently accessing and generalizing the inflectional pattern of a given form.