Genetic Influence on the Variance in Coincidence Timing and its Covariance with IQ: A Twin Study

Performance measures on a coincidence timing task have previously been associated with psychometric IQ suggesting that the ability of an individual to devote processing resources at the required time may account for some of intelligence test variance. Using the twin design, this study investigates whether genetic variability explains some of the variance in coincidence timing and whether common genetic factors account for the association with intellectual functioning. Fifty-five 16-year old twin pairs (28 MZ, 27 DZ) were tested. Individual differences in number of hits (HITS), mean absolute error (MAE), and intra-individual trial-to-trial consistency (SD) were significantly influenced by genetic factors, accounting for approximately 50 percent of the variance. The correlation between coincidence timing and psychometric IQ was confirmed and ranged from 0.11 to 0.53 with a mean correlation of 0.33. In the limited sample, the correlation between IQ and the coincidence timing measures appeared to be mediated largely by a unique environmental factor, with only a small loading of SD on the genetic factor influencing IQ. However, as the confidence intervals in the other genetic cross loadings are large, we cannot exclude the possibility of a much stronger genetic influence.