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Imaging unconscious semantic priming


Visual words that are masked and presented so briefly that they cannot be seen may nevertheless facilitate the subsequent processing of related words, a phenomenon called masked priming1,2. It has been debated whether masked primes can activate cognitive processes without gaining access to consciousness3,4,5. Here we use a combination of behavioural and brain-imaging techniques to estimate the depth of processing of masked numerical primes. Our results indicate that masked stimuli have a measurable influence on electrical and haemodynamic measures of brain activity. When subjects engage in an overt semantic comparison task with a clearly visible target numeral, measures of covert motor activity indicate that they also unconsciously apply the task instructions to an unseen masked numeral. A stream of perceptual, semantic and motor processes can therefore occur without awareness.

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Figure 1: Experimental design.
Figure 2: Behavioural priming effect.
Figure 3: ERP measures of prime–target congruity.
Figure 4: ERP measures of covert and overt motor activation.
Figure 5: fMRI measure of motor priming.


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Correspondence to Stanislas Dehaene.

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Dehaene, S., Naccache, L., Le Clec'H, G. et al. Imaging unconscious semantic priming. Nature 395, 597–600 (1998).

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