Similarity effect in morphological generalization: Using the volitional form elicited production task of Japanese verbs with <i>suru</i> ending

Abstract Two major views have been proposed regarding the mechanism underlying morphological generalization: rule-based and analogy-based mechanisms. The analogy-based mechanism is sensitive to the similarity of nonce words to existing words, whereas the rule-based mechanism is not. This study investigated the production of volitional forms of Japanese verbs whose non-past forms end with suru by using an elicited production experiment with low- and high-frequency real verbs and novel verbs with varying degrees of similarity to existing verbs. The findings are as follows: The conjugational form of the largest verb group was preferred, and an increase in the conjugational form of a smaller verb group was found only in the completely similar condition. These results can be explained by the rule-based mechanism.