Prior studies have shown that Inspection Time (IT) is moderately correlated
with IQ. Typically, investigators have asserted that a shared mental speed
factor is responsible for this correlation. Three experiments examined the
effects of practice, response strategies, and attentiveness on inspection
time and its relation to IQ. Results from Experiment 1 illustrated that IT
improves over occasions and that, with improvement, the strength of the IT-
IQ correlation is attenuated. Using accuracy rates from the longest stimulu
s durations in the IT task; as an index of attentiveness, results from Expe
riment 2 suggested that attentiveness is at least in part responsible for t
he IT-IQ correlation. Although results from Experiment 3 further suggested
that attentiveness contributes to individual differences in IT, the results
also suggest that other processes, perhaps related to mental speed, contri
bute to the IT-IQ correlation.