Correlations of movement time and intelligence: Effects of simplifying response requirements

Abstract

Research indicates that certain response parameters are related consistently to IQ. While explanations of why decision time (DT) and response variability relate to IQ have been presented, no satisfactory explanation of why movement time (MT) should be related to IQ has been advanced. One possible explanation relates to the motor response requirements of the apparatus devised by Jensen (1982) . The apparatus controls for movement distance of responses in all conditions, but in some conditions those responses must be made in different directions. Moreover, the responses must be guided to relatively small targets. The present study evaluated the hypothesis that individual differences in guidance of the motor responses may account for a portion of MT-IQ covariance. An apparatus was designed for which the motor response was to a large target and the response was the same distance and direction regardless of decision complexity. For a sample of adolescents, IQ measures were correlated with DT and MT across four levels of task complexity. The MT-IQ correlations were significant and as large as DT-IQ correlations. This finding is interpreted as evidence against the motor guidance hypothesis and suggests that alternate explanations should be investigated.