Should IQ, perceptual speed, or both be used to explain response time?

Vickers and Smith (1986) described inspection time (IT) as a single measure capable of capturing individual differences in performance. Since then, IT has been shown to correlate with intelligence quotient (IQ). In turn, IQ is a stronger correlate of response time (RT) for slower trials than for faster trials, and this is observed when IQ also correlates with the quality of stimuli or with the degree of caution from participants. The present study investigated whether IT correlates with RT and with quality of evidence or degree of caution in the same way as IQ does. Results showed that IT correlations differed from IQ correlations in a manner that could indicate task specificity. It is recommended that both IQ and IT be measured in future studies so that further empirical evidence can help establish a working hypothesis for IT and IQ as predictors of performance.