Choice reaction time and visual pathway nerve conduction velocity both correlate with intelligence but appear not to correlate with each other: Implications for information processing

Reed and Jensen (1992) studied 147 normal young adults and reported a significant positive correlation between nerve conduction velocity (NCV) in a brain nerve pathway (V:P100) and a measure of nonverbal IQ, in agreement with clinical studies. It was argued that V:P100 is a useful approximation to cortical NCV, should affect the speed of information processing (SIP), and so, should be a factor affecting IQ. In this article the choice and simple reaction times (CRT and SRT) and their differences, in the same subjects, were examined. Individual discriminative (Oddman) RT (ODRT) minus SRT (ODRT - SRT), which is the actual “cognitive time,” correlated highest with IQ: r = −.23, p = .005. CRT is also a measure of SIP so V:P100 and ODRT - SRT are expected to correlate with each other. In these 147 subjects, however, they cannot be shown to be correlated ( r = .044, p = .60; absolute true value probably < .20). This suggests that (1) there are two largely independent neurophysiological processes affecting normal intelligence, and (2) the differences among normal subjects in CRT are not entirely due to differences in mean cortical NCV. Recent electrophysiological data indicate that normal persons can have different patterns of neural connectivity among cortical regions during a visuomotor task requiring decision. Consequently, the simplest interpretation of the great ODRT -SRT variability observed among our subjects is that it reflects different total lengths of cortical pathway involved in the ODRT task, more intelligent subjects having shorter path lengths on average than less intelligent subjects. This interpretation can also explain the reported lower brain energy requirement of more intelligent persons for doing a specified mental task.