| Research Abstract |
A quasi-regularity of verb inflection, including both regular and irregular paradigms, has provided many debates and insights on how the mind is structured to differentially inflect regular and irregular verbs 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 including phonological and semantic representations, with a homogeneous structure and algorithm over neuron-like processing units, is enough to produce differential output to regular and irregular verbs.
In Japanese, almost all verbs are inflected according to one of two inflection paradigms, the typical or the atypical one, each of which has a completely predictable way of transforming a base to an inflected form across all inflectional categories like generating past-tense, indicative, negative form, and so on. However, Japan
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ese verbs have a quasi-regularity in terms of 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 reduced 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 at 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 showed impairment in production, repetition, reading, comprehension of sentences, and also syntactic tasks as well as digit span and nonword repetition. In interpreting these double dissociations, the dual-system theory assumes a damage of the symbolic rule for YT and that of the associative memory for TI while the single-system theory suggests a semantic and phonological damage for TI and YT, respectively. Less
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