Abstract
A recent model of semantic memory holds that retrieval of object knowledge is accomplished through the reactivation of perceptual feature representations. This view is supported by neuroimaging evidence of visual association-area activation during concept retrieval. However, the temporal resolution of functional MRI is unable to resolve whether perceptual retroactivation occurs at the earliest stage of conceptual processing per se, or rather is merely a later byproduct of this processing. The present study measured high-temporal resolution event related brain potentials (ERPs) in a semantic priming paradigm. The N400 component appears to be the earliest marker of conceptual processing — its amplitude is reduced when stimuli appear in a related context — and is sensitive to semantic priming. Stimuli were either pairs of words whose referents have similar shape (e.g., ‘cigarette’ — ‘chalk’), or word-picture pairs whose referents have similar typical color (e.g., ‘frog’ — [lettuce]). These respective relations and modalities were chosen to ensure that the perceptual information in question was not present in either of the stimuli (pictures were black and white line drawings); thus, any effect must be due to overlap in conceptual representations. In Experiment 1, participants made a lexical decision to words and nonwords that were preceded by shape-related or unrelated words. The shape-related condition elicited a smaller N400 component than the unrelated condition. In Experiment 2, participants named pictures that were preceded by either color-related or unrelated words. The N400 was again attenuated in the related condition relative to the unrelated condition. These results show the earliest stage of conceptual processing of a word or picture is affected by the prior presentation of a shape- or color-related word. Thus, the activation of perceptual features plays an important role in concept representation.