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Michael F. Bonner, Amy R. Price, Jonathan E. Peelle, Murray Grossman; At the interface of visual perception and long-term memory: Object knowledge and the medial temporal lobe. Journal of Vision 2013;13(9):926. doi: 10.1167/13.9.926.
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Along the ventral visual pathway, neurons are increasingly selective for complex features and invariant to low-level details. This hierarchy culminates in the medial temporal lobe (MTL), where neurons exhibit highly selective and invariant responses to objects, responding even to the spoken and written names of objects. One interpretation of these findings is that MTL neurons encode a stable representation of visual concepts, providing a link between ongoing visual perception and long-term object knowledge. We tested this MTL hypothesis in three experiments that investigate the neural basis of visual concepts. In an fMRI experiment, healthy adults (N=16) performed a semantic matching task on word triads that varied on their visual feature associations. fMRI analysis showed that visual features parametrically modulated activity in the MTL and fusiform gyrus (p<.05, whole-brain corrected), such that highly visual words resulted in increased activation. Furthermore, subjects had a processing advantage for highly visual words (faster reaction times), and structural MRI analysis revealed that individual differences in the degree of this processing advantage correlated with gray matter density of the hippocampus (rho=.7, p=.002). We next administered this task in patients with semantic dementia (N=8), a neurodegenerative condition affecting the anterior temporal lobes. We compared performance on two linguistically matched subgroups of triads: visual and abstract (mean visual association ratings=5.5 and 0.6, respectively). Controls made few errors but were worse on abstract triads (p<.05). Patients were impaired overall, but varied considerably on their performance for visual relative to abstract triads. A whole-brain regression analysis revealed a strong relationship between decreased gray matter density in the MTL and impaired knowledge of visual concepts relative to abstract concepts (p<.05, whole-brain corrected). It appears that MTL structures at the apex of the ventral visual stream may underlie the interaction of visual perception and the long-term representation of object concepts.
Meeting abstract presented at VSS 2013
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