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James J. Todd, René Marois; Posterior parietal cortex activity predicts individual differences in visual short-term memory capacity. Journal of Vision 2005;5(8):608. doi: 10.1167/5.8.608.
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Humans show a severe capacity limit in the amount of information they can store in visual short-term memory (VSTM). We recently demonstrated in an fMRI experiment that storage capacity for a visual scene (object color & location), estimated in averaged group data, strongly correlated with activity in bilateral posterior parietal/superior occipital cortex (PPC/SOC; Todd & Marois, 2004). However, individuals vary widely in their VSTM capacity, and this is reflected in their electrophysiological activity (Vogel & Machizawa, 2004). Here we re-analyzed the fMRI data of Todd & Marois (2004) to determine whether individual differences in VSTM capacity is reflected in the neural activity of specific brain regions. Subjects memorized the color and location of a variable number of discs and, following a 5s retention interval, determined whether a single disc presented in a probe display matched in location and color one of the discs in the sample display. A voxel-wise, individual differences analysis revealed a significant correlation between PPC/SOC activity and individuals' VSTM capacity. A second, slow event-related fMRI experiment showed that this relationship exists primarily during the maintenance phase of VSTM. In addition, a more sensitive, region of interest (ROI) approach suggests that visual and frontal cortex activity is weakly correlated with individual differences in VSTM capacity. Taken together, these results support a key role for the posterior parietal/superior occipital cortex in VSTM by demonstrating that its activity level predicts individual differences in VSTM capacity.
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