Intelligence as a factor in evoked potential studies of psychopathology. II. Correlations between treatment-associated changes in IQ and evoked potentials.

The first report of this series indicated that evoked potential (EP) characteristics previously shown to correlate with psychopathology differed between subjects with high and low intelligence test scores (IQ). This paper reports the results of an attempt to determine if these IQ-EP relationships could result from variations in clinical state, rather than from differences between groups in trait IQ. Two patient groups were selected on the basis of the shifts in their Raven Progressive Matrices scores from first test to retest: (i) increase of 17-46 percentile points; (ii) decrease of 5 to 30 points. Their somatosensory, visual, and auditory EPs were compared in several ways to determine if the EP changes on retest were correlated with the IQ changes, as predicted from the state hypothesis. The results did not confirm the predictions, suggesting that the previous findings reflected differences in trait IQ.