There are multiple factors that could affect block design. It does involve fine-motor skills, and obviously vision. It is also timed, which can be a factor as well.
The FSIQ is derived by summing the subtest scaled scores for the two verbal subtests, the two fluid reasoning subtests, and one each of the visual-spatial, working memory, and processing speed subtests. Then you look up norms which are based on the this sum of scores, which generate a standard score. It is not a simple average of the subtest scores.
