Authors:

Heindel, W.C., Long, V.V., Festa, E.K. & TAYLOR, J.R.

Reference:

Year of publication:

2007

CBU number:

6677

Abstract:

The N400 is influenced both by current semantic context held within working memory and by context-independent structural relations within semantic memory. The relative dependence of living and non-living objects on these two mechanisms was examined using a semantic priming paradigm that placed these mechanisms in direct opposition. Participants were shown prime-target word pairs with a low-relatedness proportion and asked to make living-nonliving category judgments to the targets: Expectancy-based context effects should lead to reverse priming due to the high percentage of unrelated word pairs (living prime strongly predicts non-living target) whereas automatic featural overlap between related primes and targets should lead to normal priming regardless of the relatedness proportion. Experiment 1, using a large non-repeated stimulus set to minimize expectancy-based effects, found normal behavioral priming at a short SOA for living but not non-living items, suggesting that priming for living items is mediated by automatic facilitation. Normal N400 priming effects were similarly observed for living but not non-living targets. Experiment 2, using a small repeated stimulus set to maximize expectancy-based effects, found reverse behavioral priming at a long SOA for both living and non-living items. While non-living items displayed a reverse N400 effect paralleling the behavioral effect, living items continued to display a normal N400 effect. These results confirm the presence of two independent contributions to the N400, and suggest that living items are processed automatically on the basis of structural relations within semantic memory whereas non-living items are dependent on controlled processing of semantic context within working memory.