Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dual-Route Processing of Complex Words: New fMRI Evidence from Derivational Suffixation

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dual-Route Processing of Complex Words: New fMRI Evidence from Derivational Suffixation

Article excerpt

Many behavioral models of the comprehension of suffixed words assume a dual-route mechanism in which these words are accessed sometimes from the mental lexicon as whole units and sometimes in terms of their component morphemes (such as happi+ness). In related neuropsychological work, Ullman et al. (1997) proposed a dual-route model for past tense processing, in which the lexicon (used for access to irregularly inflected forms) corresponds to declarative memory and a medial temporal/ parietal circuit, and the rule system (used for computation of regularly inflected forms) corresponds to procedural memory and a frontal (including Broca's area)/basal ganglia circuit. We used functional MRI and a memory encoding task to test this model for derivationally suffixed words, comparing those words that show evidence of decompositional processing in behavioral studies (-ness, -less, and -able words) with derived words that do not show decomposition effects (-ity and -ation words). By examining Broca's area and the basal ganglia as regions of interest, we found that "decomposable" derived and inflected words showed increases in activity relative to nondecomposable suffixed words. Results support a dual-route model of lexical access of complex words that is consistent with the Ullman et al. proposal.

When readers process a complex word, is it accessed from the mental lexicon as a whole word or as a collection of separable morphemes? Because prefixes and suffixes are frequent, productive, and relatively invariant forms in language, it is possible that mental representations might take advantage of this invariance by representing morphemes as separable units. In behavioral experimental work, however, effects of morphological structure on word reading are not always detected. Models of this process (Caramazza, Laudanna, & Romani, 1988; Schreuder & Baayen, 1995) suggest a dual-route mechanism in which affixed words are sometimes accessed as whole units, sometimes as component morphemes (this second process is referred to as morphological decomposition or computation). Recently, neural correlates of a dual-route mechanism have been investigated, but solely for inflected words, and particularly for the past tense (see Beretta et al., 2003; Jaeger, Van Valin, & Lockwood, 1998). By looking at derived words, this study offers further evidence based on a recent model of linguistic processing in the brain (Ullman, 2001 ; Ullman et al., 1997) for differing patterns of neural activity corresponding to whole-word and decompositional processing routes.

Whether a complex word is processed decompositionally seems to depend on the linguistic properties of the affix it includes. Regular inflectional suffixes, such as English past tense, Finnish case inflections, and the Dutch regular plural, serve a grammatical function without changing the meaning or part of speech of words to which they attach, and they consistently show evidence of morphological decomposition in behavioral studies (Alegre & Gordon, 1999; Niemi, Laine, & Tuominen, 1994). A subset of derivational suffixes, or of suffixes that do change meaning and part of speech, shows a similar pattern: For instance, suffixes like English -ness and -able or Dutch -held show evidence of decompositional processing (Bertram, Schreuder, & Baayen, 2000; Vannest, Bertram, Jarvikivi, & Niemi, 2002). These suffixes do not change the pronunciation of the base words to which they attach and are relatively productive and consistent in meaning. A different pattern, however, is found for words with derivational suffixes that can indeed change the form of base words to which they attach (e.g., serene [arrow right] serenity). These suffixed words seem to be processed as wholeword units rather than as individual morphemes (Bradley, 1980; Vannest & Boland, 1999). This pattern holds even for idiosyncratic items in which these "whole-word processed" suffixes do not produce a phonological change (e. …

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