Much earlier than N400: Word semantic priming is reflected in the N2pc ERP component.

Over the past thirty years, a flood of studies on the electrophysiology of language has consistently proposed that the N400 component in the event-related potential (ERP) generated by a verbal stimulus could be taken as a reflection of the processing of such stimulus at a semantic level. It has become traditional to conceptualize the N400 as a temporal landmark of the stage at which semantics modulate the processing of verbal stimuli, and to interpret the relationship between semantic processing and N400 as biunivocal. One experiment is presented that suggests that such an interpretation must be reconsidered. Two horizontally arrayed strings of characters were visually presented in different colors (red and green) on each trial, one to the left and one to the right of a central fixation cross. Participants were instructed to perform a lexical decision on a target string defined by color (e.g., red), while ignoring the other distractor string (green). On half of the trials, both strings were words, and the semantic relation between the word concepts was systematically manipulated. An enhanced negativity at about 200 ms after target presentation was recorded at posterior electrodes contralateral to the visual hemifield occupied by the target word (i.e., N2pc). Crucially for our purposes, the amplitude of the N2pc depended on the semantic relation between the word concepts, being smaller when the word concepts were semantically related. The conclusions relate the present evidence of early semantic activation with past conceptualizations about semantic processing.