A TWIN STUDY OF SPATIAL ABILITY.

A battery of spatial visualization land form percepthn plus some tests of arithmetic, vocabulary and social perception has been administered to 274 pairs of identical and 198 pairs of frabmal twins. To assess the importance of hereditary components in the individual differences observed, the within pair variance for fraternal paim was compared with the within pair vazianw for identical pains by the F ratio test. The results for 123 pairs of identiml twins and 91 pairs of fraternal twins on the spatial task, were classified in terms of the apparent psychological task requirements of the test. It appears that tests requiring three-dimensional manipdadion of drawings demonstrate more frequently a statistically significant hereditary component.