Inspection time correlates with general speed of processing but not with fluid ability

Inspection time (IT) has been shown to correlate reliably with putative tes ts of general intelligence such as Raven's matrices and more strongly with performance IQ than with verbal IQ from the Wechsler scales. A common inter pretation of this pattern has been that PIQ and matrices tests are measures of fluid ability (Gf) and therefore that IT provides an index of a biologi cal substrate underpinning individual differences in IQ. Marker tests for l ive of the constructs described in Gf-Gc theory of cognitive abilities were administered to a sample of 64 adults who also completed IT estimation. IT correlated -0.43 (p < 0.001) with a test of general processing speed (Gs) but did not significantly correlate with a test of Gf Results of partial co rrelation analysis and factor analysis were not consistent with the proposi tion that general intelligence depends exclusively or substantially on spee d of processing. A sub-sample of 37 subjects completed a second marker test for both Gf and Gs. The correlations with IT were consistent with those ob tained for the larger sample. The results are interpreted within a hierarch ical model of cognitive ability that incorporates speed of processing at th e same level as fluid ability and crystallized ability.