Studies investigating the functioning of persons who have cerebral lesions and evidence from the study of commisurotomized and normal subjects are reviewed. A study of recognition of pictorial stimuli by right-handed male children is also discussed. Studies about cerebral lesions and associated deficits have yielded information about the perceptual and cognitive abilities subserved by the left and right hemispheres of the brain. Two lines of inquiry concern: the study of patients who have undergone transection of the corpus collosum and observations of functional asymmetries resulting from dichotic and lateralized tachistoscopic presentation of stimuli to normal subjects. In a pictorial recognition study, 18 right-handed first, second, and third grade boys were tested. The subjects had no familial history of left-handedness. The study results clearly support the hypothesis that between the ages of five and seven a change takes place in the relative efficiency of the hemispheres for the recognition of pictorial stimuli. It is suggested that these behavioral transitions reflect a change in the relative efficiency of the hemispheres for information processing. It seems probable that in this age period previously less efficient left hemispheric verbal processes come to surpass right hemispheric processes that have an initial superiority. (SW)