Self-Organizing Dynamics of Lexical Access in Normals and Aphasics

Abstract

Abstract& The goal of this article is to illustrate the application of selforganizing dynamics in the design of a model of lexical access. We focus particularly on the mapping of sound structure on to the lexicon and the influence of that structure on lexical access. The approach is tested in a series of two sets of simulations that explicate how lexical access might occur in normal subjects and aphasic patients. Both sets of simulations address the behavioral effects of both phonological and phonetic variability of prime stimuli on the magnitude of semantic priming. Results show that the model can successfully account for the behavioral effects associated with several kinds of acoustic manipulation, competitor presence, and the unfolding of those effects over time-primarily because it balances three important control parameters: resting lexical activation, positive feedback, and negative feedback. These simulations are offered as support (in the form of an existence proof) that deficits in the degree of lexical activation can account for the lexical processing impairments shown by Broca's aphasics who have reduced lexical activation, and Wernicke's aphasics who have increased lexical activation. Overall, results suggest that the present approach promises to offer a coherent theoretical framework within which to link empirical evidence in language processing and cognitive neuroscience in terms of possible underlying mechanisms. &

An Event-Related fMRI Investigation of Implicit Semantic Priming

“…These results suggest that activation of the lexicon is graded and that the degree of activation is influenced by the phonological distance of a nonword stimulus to a lexical entry. Consistent with these findings are behavioral and modeling data showing that lexical access is influenced by the degree to which the phonetic structure of the input matches word candidates (see McNellis & Blumstein, 2001;Luce & Pisoni, 1998). The similar areas of activation in the nonword condition compared to the related and unrelated conditions (Figure 1) can likely be attributed to the fact that these pseudowords automatically activate a set of phonologically similar lexical representations.…”

Spoken-word processing in aphasia: Effects of item overlap and item repetition

“…Research results and models from auditory word recognition (cf. McNellis &Norris, 1994) should be combined with models based on tasks such as nonword repetition and serial recall (Gathercole & Baddeley, 1993;Martin & Ayala, 2004). Both research areas deal with language-impaired populations, the role of verbal short-term memory and spreading of activation within the lexical system.…”

“…Milberg, Blumstein, & Dworetzky, 1988;Misiurski, Blumstein, Rissman, & Berman, 2005;Utman, Blumstein, & Sullivan, 2001, but also see Baum, 1997;Gordon & Baum, 1994). Following Dell, Schwartz, Martin, Saffran, and Gagnon (1997) who modelled aphasic speech production errors by making global parameter adjustments to the 'normal' model, McNellis and Blumstein (2001) altered the parameter of lexical resting state to lower-than-normal for Broca's and to higher-than-normal for Wernicke's aphasics. McNellis and Blumstein showed that by such a simple parameter adjustment, experimental findings of Milberg et al (1988) and of Utman et al (2001) could be simulated.…”

“…Thus, the effect of brain damage can be regarded in terms of systemic properties, rather than in terms of impairment of specific functions localisable in the brain (cf. Dell et al, 1997;Laine, Tikkala, & Juhola, 1998;McNellis & Blumstein, 2001). In this view, normal performance is the upper limit of a performance continuum and aphasic performance is spread over the continuum.…”

Neural Systems and Language Processing: Toward a Synthetic Approach

“…It is also proposed that the dynamics of activation across the neural systems underlying language vary as a function of the particular neural system, hence resulting in such clinical syndromes as Broca's and Wernicke's aphasia and in the different patterns of performance in on-line language processing tasks shown by these patients (cf. also McNellis & Blumstein, 1999).…”