The string measure of the event-related potential, IQ and inspection time

Event-related potentials (ERPs) were recorded as subjects responded to inspection time (IT) trials with two stimulus onset asynchronies (SOAs) such that the trials were approximately equally easy or difficult for all subjects. The correlations of the string measure of the ERPs with IT estimates and scores on the digit symbol (DS) sub-test of the WAIS-R were consistent with predictions based on the Hendricksonsʹ theory of the ERP and intelligence. Correlations of the string measure with full WAIS-R scores were near zero. This is not consistent with the Hendricksonsʹ theory and is also in contrast to a recent theory, which proposes that focussed attention requirements reverse the direction of the correlation between the string measure and IQ. Procedural differences that may have influenced the correlations are discussed. The string measure also does not appear to index those features of the ERP found to correlate with IT and IQ in previous studies using similar experimental paradigms.