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Abstract:
Abstract: The temporo-spatial orchestration of conscious and
unconscious semantic processing was investigated using
event-related potentials (ERPs). In a priming paradigm, it was
assessed whether masked words, which do not enter consciousness,
activate their semantic representations and elicit behavioral and
electrophysiological priming effects upon a subsequently presented
target word. Furthermore, we examined whether masked (unconscious)
and unmasked (conscious) priming effects exhibit a different time
course of brain activations. ERPs were recorded from 64 channels
while subjects performed a lexical decision task on semantically
related or unrelated prime-target word pairings. Primes were
presented either masked by a random pattern or unmasked.
Furthermore, SOA between prime and target was either 67 ms or 200
ms. Analysis revealed behavioral priming effects in both, the
unmasked and masked, conditions. Subjects responded faster to
semantically related than to unrelated words. Likewise, conscious
and unconscious priming modulated the N400 ERP component: ERPs to
unrelated words were more negative than to related words between
350-500 ms after target presentation. However, ERP priming effects
strongly depended upon the SOA. At the very short SOA (67 ms),
both, conscious and unconscious, conditions elicited similar N400
priming effects. At the SOA of 200 ms, however, reliable N400
effects were only obtained under conscious prime presentation. The
results show that unconscious semantic brain activation as indexed
by the N400 potential decays relatively fast over a short period of
time.
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