Motivation: cause or confound in information processing/intelligence correlations?

The goal of the present study was to determine whether correlations between information processing scores and intelligence can be explained in terms of between-subject motivational differences. One hundred and nine male and female volunteer college students were tested on a battery of microcomputerized cognitive tests. One hundred of these subjects returned for a second session in which they were randomly assigned to an incentive or no-incentive condition and then retested. The effort expended on the tests was measured via heart rate, skin conductance, and a self-report questionnaire. Criterion measures, including the Advanced Otis-Lennon Test of Mental Abilities and Advanced Raven Progressive Matrices were also taken. The findings revealed that incentives had relatively modest effects on performance. In no case, however, did incentives affect the overall IQ-performance correlation for the tests used in the battery. These results support the view that correlations between information processing scores and intelligence reflect common mental capacities, rather than some affective variable such as motivation.