Activating Verb Semantics from the Regular and Irregular Past Tense

Activating Verb Semantics from the Regular and Irregular Past Tense. Catherine E Longworth (cat@csl.psychol.cam.ac.uk) Billi Randall (bjr22@cam.ac.uk) Lorraine K Tyler (lktyler@csl.psychol.cam.ac.uk) Centre for Speech and Language, Dept. Exp. Psychology, Downing Site, Cambridge, CB2 3EB, UK. William D Marslen-Wilson (william.marslen-wilson@mrc-cbu.cam.ac.uk) MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, CB2 2EF, UK Abstract Theoretical accounts of the processing of inflectional morphology make implicit, untested assumptions about the activation of verb semantics from inflected verbs. This research used semantic priming to investigate the extent to which regular and irregular past tense forms activate verb semantics, in comparison to the verb stem. The results show that past tense forms activate verb semantics to the same extent as verb stems and without differences due to verb regularity. These results provide constraining data for models of inflectional morphology. Introduction Research on the mental representation and processing of inflected words has focused on the type of underlying processing system required to account for our ability to produce and comprehend regularly and irregularly inflected words. The English past tense in particular has formed an important test case for such research. It provides a sharp contrast between the productive regular past tense and a limited set of irregular forms. Theoretical accounts divide into those suggesting that all inflected forms, both regular and irregular, are stored using associative memory (e.g. Rumelhart and McClelland, 1986) and those proposing that the predictability of the regular past tense allows us to compute the inflected forms from their verb stems using symbolically based rules (e.g. Pinker, 1991). Such accounts focus primarily on the processing and representation of the regular and irregular past tense as phonological forms, tending to neglect the important issue of how these forms contact their underlying semantic and syntactic content. Nonetheless, they incorporate assumptions, explicit or implicit, about how these inflected forms map on to their semantics. Pinker has suggested that the regular past tense is not stored in its own right but computed using symbolic rules, whereas the irregular past tense is stored independently of its stem (Pinker, 1991). Comprehension of the regular past tense is assumed to require rule-based decomposition into stem and inflection. This process may delay semantic activation relative to the irregular past tense, which is not assumed to require rule-based processing. The related account proposed by Marslen-Wilson and Tyler (1998) explicitly postulates that the regular and irregular past tense activate the semantic representations of their verb stems through different routes. The morphophonologically complex regular past tense is parsed into its stem and affix in order to access stem semantics, whereas the irregular past is recognised as a full form, which must subsequently be mapped onto verb semantics assumed to be stored at the level of the lexical entry. Strict full-listing accounts (Butterworth, 1983) suggest that all past tense forms are stored in memory, with semantic representations presumably stored independently of their verb stems. Activating such representations would not be delayed by rule-based processing, and would not be expected to differ according to morphological complexity or verb regularity. Parallel-distributed processing models (Joanisse and Seidenberg, 1999; Plunkett and Marchman, 1993; Rumelhart and McClelland, 1986) have assumed that both the regular and irregular past tense activate semantic units associated with their verb stems. In common with strict full-listing accounts, the fact that the regular and irregular past tense have differing degrees of phonological and orthographic similarity to their stems is not assumed to entail differential processing. However, if a mapping is less consistent (as in irregular forms) this may lead to slower or less efficient activation. It can be seen that although these accounts focus on the consequences of the variable predictability of past tense form from its associated verb stem, they inevitably make theoretical assumptions about the activation of verb semantics from inflected forms as well. Typically one would use semantic priming to test assumptions relating to the organisation of semantic representations or the time course of its activation. However, research using semantic priming has tended to use concrete nouns and/or uninflected verbs. This is because morphologically simple words are assumed to