The proposed twin study will use a combined psychometric and information-processing approach in examining genetic and environmental sources of individual differences in spatial performance. A sample of 72 pairs of twins (36 identical and 36 same-sex fraternal), ages 14-18, will administered spatial information-processing tasks (which were designed to estimate processes such as encoding, comparing, searching, and rotating of particular stimulus elements) and a psychometric battery of spatial-related cognitive tests. The study intends to examine the struture of the genetic and environmental correlations among the various spatial cognitive measures, as well as the etiology of the variance of each spatial measure separately. The use of a combined psychometric and information-precessing approach in conjunction with the application of multivariate behavioral genetic methods in this study can further our understanding of the etiology of spatial cognition. Further, results of this study may be of educational and medical significance to individuals with spatial-cognitive disorders.