Complementarity or independence of hemispheric specializations? A brief review.

The current review investigates the question of the relationship of different hemispheric specializations. Hemispheric specializations are the result of the seemingly distinctive ability of the left and right hemisphere to specialize in different cognitive functions. The review focuses on the concept of complementarity whereby the lateralization of one function predicts the asymmetric processing of another one. The complementarity of hemispheric specializations presents an interesting dilemma as the literature evidence is outwardly mixed. The causal and statistical hypotheses attempt to account for the observed findings, with support for both hypotheses. However, most of the evidence appears to align with the statistical pattern of complementarity. Converging lines of evidence suggest that there are multiple independent biases that play a role in how these functional cerebral asymmetries are organized in the human brain. Some of the functional and evolutionary implications of the existence of complementarity of hemispheric specializations are also briefly discussed.