Most words in natural language are polysemous, that is, they can be used in more than one way. For example, paper can be used to refer to a substance made out of wood pulp or to a daily publication printed on that substance. Although virtually every sentence contains polysemy, there is little agreement as to how polysemy is represented in the mental lexicon. Do different uses of polysemous words involve access to a single representation or do our minds store distinct representations for each different sense? Here we investigated priming between senses with a combination of behavioral and magnetoencephalographic measures in order to test whether different senses of the same word involve identity or mere formal and semantic similarity. Our results show that polysemy effects are clearly distinct from similarity effects bilaterally. In the left hemisphere, sense-relatedness elicited shorter latencies of the M350 source, which has been hypothesized to index lexical activation. Concurrent activity in the right hemisphere, on the other hand, peaked later for sense-related than for unrelated target stimuli, suggesting competition between related senses. The obtained pattern of results supports models in which the representation of polysemy involves both representational identity and difference: Related senses connect to same abstract lexical representation, but are distinctly listed within that representation.

The current study addresses the controversial issue of how different grammatical categories are neurally processed. Several lesion-deficit studies suggest that distinct neural substrates underlie the representation of nouns and verbs, with verb deficits associated with damage to left inferior frontal gyrus (LIFG) and noun deficits with damage to left temporal cortex. However, this view is not universally shared by neuropsychological and neuroimaging studies. We have suggested that these inconsistencies may reflect interactions between the morphological structure of nouns and verbs and the processing implications of this, rather than differences in their neural representations (Tyler et al. 2004). We tested this hypothesis using eventrelated functional magnetic resonance imaging, to scan subjects performing a valence judgment on unambiguous nouns and verbs, presented as stems (‘snail, hear’) and inflected forms (‘snails, hears’). We predicted that activations for noun and verb stems would not differ, whereas inflected verbs would generate more activation in left frontotemporal areas than inflected nouns. Our findings supported this hypothesis, with greater activation of this network for inflected verbs compared with inflected nouns. These results support the claim that form class is not a first-order organizing principle underlying the representation of words but rather interacts with the processes that operate over lexical representations.

Five unmasked- and four masked-priming lexical decision experiments were carried out in Spanish in order to probe the data structures and processing routines that are exploited during the comprehension of inflected words. In unmasked priming, responses to targets (e.g., mor-os `Moors') were inhibited when they were preceded by stem-homograph primes (mor-ir `to die') compared to unrelated control primes (sill-a `chair'), and this inhibitory effect was over and above a weak inhibitory effect found for orthographic relative primes (moral `moral'). Stemhomograph inhibition is interpreted as a consequence of morphological decomposition in lexical access. In additional experiments, this inhibitory effect was observed when targets were preceded by primes that were not themselves stem-homographic with the target, but rather were stemallomorphic variants of the stem-homograph words (muer-e `she/he/it dies'). Because target inhibition was found for primes whose inflectional stems are not strictly ambiguous in terms of form, it suggests that the inhibitory effect arises at a level where form-neutral, morphologically abstract (lemma) representations are encoded. The results observed in masked (subliminal) priming contrast with those observed in unmasked priming. When the primes were presented subliminally, stem-homograph priming (mor-a ---mor-os) was facilitative, while orthographic relative priming (moral ---mor-os), was neither facilitative nor inhibitory. This was taken as further evidence that stems are decomposed at the form level, and that ambiguous decomposed stems, such as mor-, activate multiple (compatible) lemma representations during the initial stages of lexical access. Moreover, the facilitative effect observed in masked stem-homograph priming suggests that the lem...

www.elsevier.com/locate/jml Morphological decomposition in early visual word processing �