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 rela ted words, a phenomenon called masked priming(1,2). It has been debate d whether masked primes can activate cognitive processes without gaini ng access to consciousness(3-5). Here we use a combination of behaviou ral and brain-imaging techniques to estimate the depth of processing o f masked numerical primes. Our results indicate that masked stimuli ha ve a measurable influence on electrical and haemodynamic measures of b rain activity, When subjects engage in an overt semantic comparison ta sk with a clearly visible target numeral, measures of covert motor act ivity indicate that they also unconsciously apply the task instruction s to an unseen masked numeral. A stream of perceptual, semantic and mo tor processes can therefore occur without awareness.