Auditory inspection time and intelligence: What is the direction of causation?

Inspection time (IT) is an index of speed of perceptual processing that correlates at moderate levels with tests of mental ability. A key issue has been the question of the direction of causation: is IT causal to individual differences in intellectual ability, or is a fast IT a consequence of having a high IQ? The direction of causation was assessed by administering auditory inspection time (AIT) tests and tests of verbal and nonverbal ability to 104 school children at age 1 1, and 2 years later at 13 years. Three competing structural equation models were tested by using the cross-lagged panel data: that AIT at age 11 causes later IQ; that IQ at age 11 causes later AIT; and that there is equal reciprocal causation. Various goodness-of-fit indexes indicated that the first model was the most acceptable. AIT accounted for about 6% of the variance in cognitive ability 2 years later