IT, IQ and perceptual speed

Although it is now beyond dispute that measures of inspection time (IT) are significantly correlated with IQ scores, the basis of this association is less clear. One suggestion is that IT provides a measure of the biological basis of g. Another is that IT is simply associated with a factor of perceptual speed (Gs in the Horn–Cattell model), which is, of course, also associated with other IQ measures. Sixty-seven sixth-form students performed an IT task and were also given tests of vocabulary, abstract reasoning and perceptual speed. Forty-three also completed a test of spatial ability. IT correlated significantly only with measures of perceptual speed (0.43) and abstract reasoning (0.29) but the partial correlation between IT and reasoning was only 0.15 when perceptual speed was taken into account.