Jensen's Reaction-Time Studies: A Reply to Longstreth

Abstract Longstreth's (1984) critique of Jensen's research on the relationship of IQ to individual differences in visual reaction time (RT), measured in the Hick paradigm, is found to have numerous errors of fact and interpretation, some trivial and some of theoretical importance. Longstreth's narrowly focused and conjectural style of criticism, which peculiarly strains to favor the null hypothesis, unfortunately obscures the essential findings of Jensen's (and others') studies of the RT-IQ relationship. The two main negative verdicts of Longstreth's critique concerning the RT-IQ relationship are refuted by meta-analyses of presently available data. First, not only do individual differences in RT show a significant negative correlation with IQ, but individual differences in the slope of the regression of RT on stimulus set size scaled in bits (i.e., the binary logarithm of the number of potential reaction stimuli) also show a fully significant, albeit low, negative correlation with IQ. Contrary to Longstreth's second negative surmise, meta-analysis also shows that the magnitude of the RT-IQ correlation itself is a linearly increasing (negative) function of stimulus set-size scaled in bits.