Broad generalizations are often made in popular psychology about one side or the other having characteristic labels, such as "logical" for the left side or "creative" for the right. These labels are not supported by studies on lateralization, as lateralization does not add specialized usage from either hemisphere. Both hemispheres contribute to both kinds of processes. and experimental evidence provides little support for correlating the structural differences between the sides with such broadly-defined functional differences.

The extent of any modularity, or specialization of brain function by area, remains under investigation. If a specific region of the brain, or even an entire hemisphere, is either injured or destroyed, its functions can sometimes be assumed by a neighboring region in the ipsilateral hemisphere or a corresponding region in the contralateral hemisphere, depending upon the area damaged and the patient's age.

Brain function lateralization is evident in the phenomena of right- or left-handedness and of right or left ear preference, but a person's preferred hand is not a clear indication of the location of brain function. Although 95% of right-handed people have left-hemisphere dominance for language, 18.8% of left-handed people have right-hemisphere dominance for language function. Additionally, 19.8% of the left-handed have bilateral language functions. Even within various language functions (e.g., semantics, syntax, prosody), degree (and even hemisphere) of dominance may differ.

Additionally, although some functions are lateralized, these are only a tendency. The trend across many individuals may also vary significantly as to how any specific function is implemented. The areas of exploration of this causal or effectual difference of a particular brain function include its gross anatomy, dendritic structure, and neurotransmitter distribution. The structural and chemical variance of a particular brain function, between the two hemispheres of one brain or between the same hemisphere of two different brains, is still being studied. Short of having undergone a hemispherectomy (removal of a cerebral hemisphere), no one is a "left-brain only" or "right-brain only" person.