The Japanese journal of neuropsychology

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ArticleTitle	A recent topic in cognitive neuropsychology -Normal and impaired patterns of morphological processing-
Language	J
AuthorList	Takao Fushimi¹⁾, Mutsuo Ijuin¹⁾, Naoko Sakuma¹⁾, Itaru F. Tatsumi¹⁾, Noriko Haruhara²⁾, Kenjiro Komori³⁾, Takako Shinkai⁴⁾
Affiliation	1) Language, Cognition, and Brain Science Research Group, Tokyo Metropolitan Institute of Gerontology 2) Department of Rehabilitation, Saiseikai Central Hospital 3) Department of Neuropsychiatry, Ehime University School of medicine 4) Department of Rehabilitation, The Second Branch of Nippon Medical School
Publication	Japanese Journal of Neuropsychology: 20 (1), 51-62, 2004
Received
Accepted
Abstract	The quasi-regularity of verb inflection, including both regular and irregular paradigms, has provided many controversies and insights on how the mind is structured to inflect regular and irregular verbs differentially into their past-tense form. One view assumes that two separate systems are involved in verb inflection, with a symbolic rule for regular and nonce verbs, and an associative memory for irregular verbs. Another view assumes that a single connectionist system—which includes phonological and semantic representations, with a homogeneous structure and algorithm over neuron-like processing units—is sufficient to produce differential output to regular and irregular verbs. In Japanese, almost all verbs are inflected according to one of two inflection paradigms: typical and atypical. Each of these has a completely predictable way of transforming a base to an inflected form across all inflectional categories like the generating past-tense, the indicative, the negative form, and so on. However, Japanese verbs have a quasi-regularity regarding which paradigm should apply to each verb. Depending on phonological overlap to atypical verbs, typical verbs were categorized into those with various degrees of consistency of form-paradigm correspondences. Experiments on Japanese skilled speakers revealed that: (1) speed and/or accuracy of inflecting real verbs decreased as consistency decreased, especially for low-familiarity verbs; (2) familiarity effects were more pronounced in less consistent verbs; and (3) assignment of the atypical paradigm to nonce verbs increased as a function of decreasing consistency. These results are consonant with the single-system theory while provide constraints on the dual-system theory so that only the most consistent verbs should be inflected by the symbolic rule, with other less consistent and atypical verbs handled by the associative memory. In a study of verb inflection with brain-damaged patients, a patient (TI) with semantic dementia demonstrated a disproportionate deficit in inflecting atypical verbs as compared with consistent-typical verbs and nonce verbs whereas a patient (YT) with conduction aphasia exhibited the reverse pattern. TI was also impaired in word comprehension, picture naming, reading aloud words with atypical print-sound correspondences—especially for low-frequency words—as well as word fluency and object recognition tasks. YT was impaired in production, repetition, reading, and comprehension of sentences, and also in syntactic tasks as well as in digit span and nonword repetition. In interpreting these double dissociations, the dual-system theory assumes a damage of the symbolic rule in the case of YT and that of the associative memory in the case of TI whereas the single-system theory suggests a semantic and phonological problem in the case of TI and YT, respectively.
Keywords	verb inflection, dual-system hypothesis, single-system hypothesis, double dissociation