Just as might be expected, a Signer with a right hemisphere lesion may become unable to use or to understand these particular grammatical constructions, while retaining perfect command of all the rest of Sign. Even in the strongly asymmetrical human brain, the left hemisphere is by no means devoid of visuo-spatial function . However, the visuo-spatial deficits produced by left parietal lobe damage are not the mirror image of the right parietal lobe syndrome. With finger agnosia comes the loss of the ability to do even the simplest arithmetic. The seeming indifference of right parietal lobe patients to their defects brings up the matter of emotional expression.
Clinical cases suggest that they handle emotional expression.
The right parieto-temporal area perceives emotional expression in the faces or voices of others. The right frontal area puts expression into the patient's own voice or face. A schoolteacher who had suffered a small right frontal lobe stroke was not much inconvenienced by the spastic paresis of her left arm, being right-handed anyway, but had to quit teaching because she could no longer control a class. Many a patient who cannot express their simplest wants in speech may, if stressed, become unexpectedly fluent in swearing. Another aspect of right hemisphere function is shown when patients who cannot repeat simple spoken phrases do much better in repeating sung phrases, both the words and the music.