Electrical potentials of the cerebral cortex and psychometric intelligence

Contradictory findings concerning relationships between intelligence-test scores and different EEG evoked-potential (EP) measures have been reported. The positive findings suggest that intelligence is correlated with the number and amplitude of components in the EP waveform. Since there is evidence that both of these parameters are influenced by stimulus intensity, we examined the extent to which an EP/intelligence relationship may depend on stimulus intensity. In a sample of 22 Ss a relationship between EP amplitude and intelligence was found and the magnitude of this correlation was related systematically to stimulus intensity. The maximum correlation (r = 0.69) with scores on the Raven's Advanced Progressive Matrices was obtained at an intermediate level of intensity. These findings may account for some of the inconsistencies in the literature. Moreover, they suggest an explanation for higher general intelligence in terms of greater central activation of neural processes in response to normal levels of stimulation.