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Paige Scalf, Paul Dux, René Marois; Working memory consolidation delays top-down attentional processing in visual Cortex: A time-resolved fMRI study. Journal of Vision 2009;9(8):175. doi: 10.1167/9.8.175.
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The consolidation of information into working memory (WM) can delay central processing of subsequent events. WM, however, is also believed to control the deployment of top-down attention (DeFockert et al., 2001). We therefore used time-resolved fMRI to investigate whether WM consolidation also delays perceptual processing of subsequently presented targets. In each trial, a masked target (T1; 400 ms display, 100 ms mask) preceded a second unmasked target (T2) by either a short (550ms) or long (1450ms) SOA. To perform the T1 task, participants encoded the identity and location of four distinct keyboard symbols and made an un-speeded response to a probe stimulus at trial's end. To perform the T2 task, participants made a speeded identity response to four identical, adjacent letters (‘H’ or ‘S’). In separate fMRI runs, participants performed either the T1 task alone, or both tasks. In the dual-task condition, T2 response time (RT) was greater at the short than at the long SOA, suggesting that T2 processing was delayed by T1 performance in the former condition. To determine whether T1 processing also delayed top-down attentional enhancement of T2, we examined T2 BOLD response in visual cortex (left middle occipital gyrus; Sergent et al., 2005) by subtracting the single-task waveforms from the dual-task waveforms for each SOA. The resulting timecourses revealed that T2 BOLD response was delayed at the short SOA relative to the long SOA. Furthermore, the magnitudes of participants' T2 BOLD delays correlated with their T2 RT delays. A follow-up experiment, in which substituting a simple detection task for the T1-encoding task eliminated the T2 BOLD response delay, confirmed that our previous results were caused by WM. We conclude that consolidation of a stimulus into WM delays the deployment of attention to subsequent target representations in visual cortex.
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