Fig. 3. Factor structure and genetic and environmental variance common across the six tests of spatial orientation.

We applied the common pathway model to parse the genetic (A), shared environmental (C) and nonshared environmental (E) variance that is shared across all the tests (represented by the A, C and E paths leaving from the common Navigation factor) from the genetic and environmental variance that is specific to each test (indexed by the individual A, C, and E latent factors from each rectangle). Each individual test loaded substantially onto a common factor, which we named Navigation factor (loadings ranging from λ = 0.54 for scanning ability to λ = 0.75 for navigation based on landmarks). All A, C, and E paths are standardized and squared.