INTELLIGENCE AND COMPLEXITY OF THE AVERAGED EVOKED-POTENTIAL - AN ATTENTIONAL THEORY

Although the Hendricksons have proposed that the string length measure of human auditory evoked potential complexity is positively related to psychometric intelligence, this relationship is variable and may even in some circumstances be reversed. Previous studies relating string length to IQ are reviewed and it is proposed that inconsistencies between these reports reflect procedural differences in task-attention requirements or the absence thereof. In order to test this hypothesis, 21 subjects participated in two string length conditions: one in which attention was not required and one in which subjects were required to count oddball stimuli. String length was shown to be the product of an interaction between intelligence and attention such that high-IQ subjects recorded lower brain evoked potential string lengths in the attend condition, whereas low-IQ subjects showed maximal string lengths under attended conditions. This result is compatible with both the D.E. Hendrickson and Hendrickson (1980) and Bates and Eysenck (1993) findings of positive and negative IQ-string correlations, respectively, and supports the hypothesis that string length indexes efficiency and capacity under attended and unattended conditions, respectively. The string length correlation with IQ is thus suggested to result from opposite attention-induced changes in string length in high- and low-IQ subjects. This was supported by a correlational analysis of the difference in string length between high and low attention conditions revealing a wide spread high correlation maximal at frontal sites, where the difference measure accounted for over half the variance in intelligence test scores (uncorrected R(2) = 0.53). It is suggested that the string difference measure is a more reliable estimate of intelligence than raw string length in either attended or unattended conditions. The neural-efficiency model of intelligence is discussed in light of these experimental findings.