Aphasic patients occasionally manifest a dissociated naming ability between objects and actions: this phenomenon has been interpreted as evidence of a separate organization for nouns and verbs in the mental lexicon. Nevertheless, Bird, Howard and Franklin (2000) suggested that the damage underlying noun-verb dissociation affects the corresponding semantic concepts and not the lexical representation of words; moreover they claimed that many dissociations reported in literature are caused merely by a strong imageability effect (Bird, Howard and Franklin, 2000; 2003). In fact, most authors used a picture naming task to assess patients' naming ability and, due to the fact that this test involves the use of pictures to represent actions and objects, nouns were frequently more imageable than verbs (Luzzatti at al., 2002). In order to overcome this drawback, we devised a new task -Nouns and Verbs Retrieval in a Sentence Context (NVR-SC)-in which nouns and verbs have the same imageability rate. Patients' performance on this task is compared with that obtained by the same patients on a standard picture naming task. Of the sixteen aphasic patients with a selective verb deficit, as revealed by the picture naming task, two continued to show dissociation in the NVR-SC task, while fourteen did not. The data indicate that at least some patients have an imageability-independent lexical deficit for verbs. The functional locus/i of the damage is also considered, with particular reference to the lemma/lexeme dichotomy suggested by Levelt et al., (1999).
Despite considerable research interest, it is still an open issue as to how morphologically complex words such as "car+s" are represented and processed in the brain. We studied the neural correlates of the processing of inflected nouns in the morphologically rich Finnish language. Previous behavioral studies in Finnish have yielded a robust inflectional processing cost, i.e., inflected words are harder to recognize than otherwise matched morphologically simple words. Theoretically this effect could stem either from decomposition of inflected words into a stem and a suffix at input level and/or from subsequent recombination at the semantic-syntactic level to arrive at an interpretation of the word. To shed light on this issue, we used magnetoencephalography to reveal the time course and localization of neural effects of morphological structure and frequency of written words. Ten subjects silently read high- and low-frequency Finnish words in inflected and monomorphemic form. Morphological complexity was accompanied by stronger and longer-lasting activation of the left superior temporal cortex from 200 ms onwards. Earlier effects of morphology were not found, supporting the view that the well-established behavioral processing cost for inflected words stems from the semantic-syntactic level rather than from early decomposition. Since the effect of morphology was detected throughout the range of word frequencies employed, the majority of inflected Finnish words appears to be represented in decomposed form and only very high-frequency inflected words may acquire full-form representations.
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