Monitoring in language perception: evidence from ERPs in a picture-sentence matching task.

P600 effects have been observed after syntactic ambiguous sentences, after several types of syntactic and semantic anomalies and after orthographic anomalies. On the basis of these findings, several investigators propose the P600 effect to reflect syntactic repair or syntactic restructuring. According to our Monitoring Theory the P600 effect reflects more general sentence reanalysis, to check whether the input sentence has been perceived appropriately. When the brain encounters a highly unexpected linguistic event, a conflict arises between the expected representation and the representation derived from the input. This conflict is proposed to trigger a process of reanalysis. In the present study, expectancy was manipulated by varying the truth-value of a sentence in relation to a picture. ERPs were recorded from 27 electrodes while we presented participants (N=30) pictures of spatial arrays followed by a sentence giving a correct or incorrect description of the picture. The mismatches were predicted to create a conflict between the conceptual representation on the basis of the picture and the actual sentence and should therefore lead to a P600. A P600 effect was indeed observed after both intra-dimensional square triangle--'the triangle stands in front of the square.', and extra-dimensional square triangle--'the triangle stands below the square.' mismatches. The present results support our Monitoring Theory; that is, the function of reprocessing reflected by the P600 effect is not purely syntactic repair or restructuring but is more general in nature, to check for possible processing errors.