Speech representation in an unbiased sample of left-handers.

The incidence of left-handedness in a consecutive series of 520 patients selected only for unilateral damage (the majority were strokes), was found to be within normal limits. Left-handers in this sample did not have a higher incidence of aphasia or apraxia than right-handers, although aphasia and apraxia tended to be less severe in left-handers. Statistical evaluation of most previous studies claiming higher frequencies of aphasia in left-handers did not substantiate those claims, except in severely disruptive pathologies. Previous studies employing the sodium Amytal test indicate bilateral speech organization in only a small percentage of left-handers. Although the Amytal data primarily sample cases of long-standing electrographic abnormality which might affect organization for language function, the dichotic listening data from the present study on adult lesions of recent onset are in excellent agreement with the Amytal studies. On the whole, the findings suggest a negligible role of the right-hemisphere in speech function in most left-handers who do not have early left-hemisphere damage. Nevertheless, this ancillary role may be detected, either as a transient effect in cases of sudden pathology, or as a higher frequency of persistent speech disorders in widespread or rapidly progressive pathology.