Manual asymmetries: feedback processing, output variability, and spatial complexity-resolving some inconsistencies.

There is considerable evidence to document the case that the preferred hand is demonstrably superior for a number of manual tasks, although the mechanisms underlying this effect are less clear. Two perspectives have been dominant; one that emphasizes differential efficiency of feedback processing and one that suggests that asymmetries are a function of increased variability of output for the nonpreferred hand. This review considers the mediating effect of the complexity of the visual space in which aimed movements occur. Some inconsistencies may be resolved by noting the superiority of the right cerebral hemisphere for manipulation of spatial relationships. A multilevel, transactional perspective, which must then be adopted, may accommodate both feedback processing and motor output variability.