THE SUPPRESSED RELATIONSHIP BETWEEN IQ AND THE REACTION TIME SLOPE PARAMETER OF THE HICK FUNCTION

Abstract The two parameters of the Hick paradigm, the intercept (a) and the slope (b), of reaction time (RT) as a function of the information load scaled in bits (i.e., the binary logarithm of the number of stimulus-response alternatives) differ in their (negative) correlation with IQ, a generally having a larger correlation than b. The typically low and often nonsignificant correlation between b and IQ appears to contradict the theory that rate of information processing is a component of general mental ability (g) as approximated by IQ or other highly g-loaded tests. The a of the Hick function largely reflects individual differences in the sensory-motor lags in task performance, while the b supposedly reflects individual differences solely in the rate of information processing. Hence b theoretically should be more highly correlated with g or its proxy, IQ, than is a. But in fact, the opposite is commonly found. The weakness of the b × IQ correlation, as compared with the correlation between IQ and a (and with other variables derived from the Hick paradigm) is mainly attributable to statistical artifacts that suppress the b parameter's correlation with any other variables, e.g., a and IQ. When the b × IQ correlation is estimated under conditions that reduce the statistical suppression of this relationship, the correlation is appreciably increased and is consistent with prediction from information processing theory.