Event-related brain potentials reflect semantic priming in an object decision task

Subjects made speeded object decisions about target line drawings which were preceded by semantically related or unrelated prime line drawings. One hundred of the targets depicted real objects and 50 others were unrecognizable non-objects. Similar to a recent picture-matching study, the ERPs from this study generated a larger negativity for unrelated than for related target pictures, between 325 and 550 msec (N400). Although these differences had a similar time course to those seen for the N400 component in semantic priming lexical decision tasks, they were more frontally distributed and were larger over the left rather than the right hemisphere. Non-objects, which were the picture equivalent of pseudowords, produced an even larger negativity with a somewhat different distribution. The results are discussed with regards to recent claims about amodal conceptual memory processes.