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Parametric study of visual word processing combining MEG and fMRI| old_uid | 2537 |
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| title | Parametric study of visual word processing combining MEG and fMRI |
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| start_date | 2007/03/26 |
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| schedule | 15h30-17h30 |
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| online | no |
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| location_info | salle Beckett |
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| summary | I will report preliminary findings of a multi-modal imaging study of visual word processing designed to test the possibility of analyzing single trials of imaging experiments via correlations with continuous stimulus variables (Hauk et al 2006). Visual word processing has been one of the central domains of research in the cognitive, and neurocognitive, study of language. While behavioral paradigms have provided much insight into to the role of a number of lexical dimensions in word processing, reaction time, being a delayed, dense, measure shed only little light on the fine temporal structure of lexical access. Hemodynamic imaging technics on their own allow for the localization of different aspects of visual word processing but lack the temporal resolution that is required for the interpretation of the localization results. Electrophysiological methods provide high temporal resolution but lack in spatial resolution. Our multi-modal study benefits from the high spatial resolution of fMRI and the temporal resolution of MEG. Another problem in the study of lexical access (and of language more generally) has been the fact that many different lexical dimensions (e.g. frequency and length) covary to a very high degree. This property makes the widely used subtraction design problematic. Following the approach of Hauk et al, we opted for a fully parametric design. Subjects performance on a lexical decision task was monitored using Magnetoencephalography (MEG) and trial related Functional Magnetic Resonance Imaging (fMRI) (two separate sessions). In the parametric design, each item was coded for 'string properties' (length, average bigram count and size of orthographic neighborhood) and 'lemma properties' (token frequency and imageability). Parameters were drawn from The English Lexicon Project (Balota et al 2002) and MRC Psycholinguistic Database (Wilson 1988). Words were chosen to vary continuously along all stimulus dimensions and such that the stimulus variables themselves were maximally decorrelated. The fMRI data provided spatial localization of parameter-related activation while the MEG data was used for temporal localization, with individual trial data correlated with stimulus variables ms by ms. Furthermore, individual subject structural MRI and fMRI data were used to constrain the MEG forward model (MNE software, Martinos Center MGH). In this talk I will discuss in particular spatio-temporal activation patterns in and around the Word Form Area (Cohen et al 2000) in the context of the debate regarding the putative role of this area in visual word processing. |
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| responsibles | <not specified> |
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