Electrophysiological correlates of direct versus indirect semantic primingin normal volunteers

The N400 component of event related potentials (ERP) was studied in 27 righ t-handed healthy subjects in a speeded lexical decision task. The semantic distance between primes (always words) and targets (50% words, 50% non-word s) was systematically varied. Prime-target relations included directly rela ted words (hen-egg), indirectly related words (lemon-sweet), and non-relate d words (sofa-wing). ERPs were recorded from 20 scalp electrodes positioned according to the international 10-20 system. The N400 reflected semantic d istance with the most negative and latest N400 peak in the non-related cond ition, the least negative and earliest N400 peak in the direct condition an d the peak in the indirect condition in-between. Hence, N400 priming effect in the indirect condition was obtained in the absence of strong sentential constraints and even though the mediating word was physically not present. (C) 1999 Elsevier Science B.V. All rights reserved.