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| Evelyn Eger |
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Dept of Neurology, J.-W.-Goethe-University, Schleusenweg 2-16, 60528 Frankfurt, Germany
e-mail: eger@em.uni-frankfurt.de |
Poster Presentation: |
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| A SUPRAMODAL REPRESENTATION OF NUMBERS IN HUMAN INTRAPARIETAL CORTEX. |
| E. Eger, P. Sterzer, M.O. Russ, A.-L. Giraud, A. Kleinschmidt | |
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Dept of Neurology, J.-W.-Goethe-University, Schleusenweg 2-16, 60528 Frankfurt, Germany |
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| Theoretical accounts of number processing as Triple Code Theory (Dehaene 1992) assume in addition to modality specific symbolic number representations an abstract semantic ?number sense? with parietal cortex as a potential substrate. Previous functional neuroimaging studies found intraparietal cortex activations in different number processing tasks but pooled stimulus-driven and task-related effects, leaving open the question whether parietal cortex is recruited by the mere presentation of numbers without a task as e.g. calculation that explicitly requires access to numerical magnitude. We performed event-related fMRI in 9 healthy subjects, presenting in randomized order visual numbers, letters and colors as well as spoken letters, number and color words. Subjects had to monitor stimuli for the occurrence of certain target items (one per category, same across modalities). We found a behavioral main effect of modality (longer reaction times for auditory targets) but no difference in the critical comparisons between visual numbers and letters, or auditory numbers and colors. Analysis of the imaging data (SPM99) focused on non-target items. Modality-specific activations in visual and auditory associative areas showed no differential response to numbers compared to the control stimuli, suggesting well matched sensory features. Testing our central hypothesis, numbers compared with letters and colors across modalities revealed activations in bilateral posterior intraparietal cortex. This effect held when masking with contrasts of numbers compared to all single control conditions and was confirmed by a conjunction analysis. Our results show an implicit and supramodal activation of intraparietal cortex by numbers that might underlie automated access to an abstract magnitude representation. |
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