Cerebral lateralization refers to the functional specialization of the left and right hemispheres. The left hemisphere is dominant for language (in ~95% of right-handers and ~70% of left-handers), sequential processing, and fine motor control. The right hemisphere is dominant for spatial processing, face recognition, emotional processing, and global/holistic processing. However, most cognitive functions involve both hemispheres working together through the corpus callosum.
Split-Brain Research
Roger Sperry and Michael Gazzaniga's studies of split-brain patients (whose corpus callosum was severed to treat epilepsy) provided dramatic evidence for lateralization. When information was presented to only one hemisphere, the left hemisphere could describe it verbally while the right hemisphere could not — but the right hemisphere could respond nonverbally (pointing, drawing). These studies revealed that each hemisphere has its own perceptions, memories, and response capabilities, and earned Sperry the Nobel Prize in 1981.
The popular notion of "left-brain" and "right-brain" people is a myth. While lateralization is real, virtually all cognitive tasks engage both hemispheres to varying degrees. Individual differences in lateralization are continuous rather than categorical. Neuroimaging reveals bilateral activation for most tasks, with relative (not absolute) hemispheric specialization. The corpus callosum enables rapid interhemispheric communication, ensuring that the two hemispheres work as an integrated system.