Acceptability Ratings of Regular and Irregular Past-tense Forms: Evidence for a Dual-system Model of Language from Word Frequency and Phonological Neighbourhood Effects

What are the computational and representational bases of the mental lexicon of words, and of the rules of grammar which productively combine lexical forms into larger words, phrases and sentences? ‘‘Dual-system’’ theories posit that lexical forms with non-compositional (arbitrary) sound-meaning pairings are stored in memory, whereas compositional structures are subserved by a distinct rule-processing system. ‘‘Single-system’’ theories claim that lexicon and grammar are both subserved by a single associative memory. Investigations of English past tense may help to resolve this controversy. On the dual-system view, irregular past-tense forms (e.g. blow– blew) are retrieved from memory, whereas regular past-tense forms (e.g. walk–walked) are produced by the application of an -ed-sufŽxation rule. On the single-system view, both types of past-tense forms are learned and computed in associative memory. To test these competing theories, acceptability ratings were elicited from native English-speaking adults for regular and irregular past-tense forms, and their stems, in sentence contexts. Partialling out stem ratings, ratings of irregular past-tense forms (blew) correlated with their frequencies and with measures of the number of similarsounding irregular verbs (threw, grew), whereas ratings of regular part-tense forms (walked) did not correlate with their frequencies or with measures of the number of similar-sounding regular verbs (stalked, balked). The results suggest that irregular past tenses are retrieved from associative memory, whereas regular past tenses are produced by a sufŽxation rule.