Cerebral control for speech in right-handers and left-handers: an analysis of the views of Paul Broca, his contemporaries, and his successors.

According to several recent historical accounts, Broca (1865a) stated that left-handers are the mirror-reverse of right-handers for cerebral control of speech, with the right hemisphere being dominant in left-handers, and the left hemisphere dominant in right-handers. The same accounts then note Broca's error in light of current evidence that the majority of left-handers are left-dominant for speech just as are nearly all right-handers. Eling (1984) has called such statements misrepresentations of Broca's position and has argued that Broca's analysis actually was more compatible with the current view that there is a disjunction, meaning an absence of an intimate anatomical relationship, between cerebral control for handedness and speech. The current paper looks again at Broca's work, describes the context in which his views were first articulated, and traces the development of the mirror-reversal principle. The conclusion is reached that, judged by a narrow reading of the 1865 paper, Broca's views could indeed be construed as an anticipation of the modern disjunction principle. However, judged by a broader reading, by consideration of his other writing, and in the context of the philosophical and scientific tradition that shaped his work, it is suggested that it was the mirror-reversal principle to which Broca was actually disposed.