SPEECH 



1719 



arrested. More interesting, perhaps, is the fact that 

 stimulation of certain additional areas within the 

 dominant hemisphere alone will also provoke speech 

 arrest. This phenomenon is rather more complex, 

 taking the form of transient verbal amnesia or occa- 

 sionally paraphasic speech ('aphasic arrest'). It may 

 be elicited by stimulation within the inferior frontal, 

 posterior parietal and posterior temporal regions of 

 the cortex (fig. 5). Whereas ordinary speech arrest, 

 as induced by appropriate stimulation of either 

 hemisphere, presents as a transient paresis or dys- 

 praxia of articulation, the inhibition induced by 

 stimulation within the above regions of the dominant 

 hemisphere can be represented as a genuine disturb- 

 ance of word-finding and speech control. This form 

 of speech arrest is obviously related to true dysphasia, 

 more especially its paroxysmal forms (50). 



Cerebral Dominance 



It has been known since the clays of Broca that 

 aphasia and kindred disorders of speech bear a special 

 relation to lesions of the left cerebral hemisphere. 

 This has traditionally been taken to impK ,1 relation- 

 ship between handedness and control of speech by 

 the hemisphere contralateral to the preferred hand. 

 Although the classical rule relating right-handedness 

 and left cerebral dominance has not been seriously 

 challenged, it cannot now be said that left-handed- 

 ness necessarily implies comparable dominance ol tin 

 right hemisphere (27, 33, 44, 57, 106, 107, 141 1. 

 Whereas it rem. tins true thai aphasia from right-sided 

 lesions is much more common in sinistrals than in 

 dextrals, left-sided lesions in sinistrals appear to 

 cause aphasia at least .is often as do lesions of the 

 right hemisphere. Indeed the reported cases in which 

 a left-handed patient owes his aphasia to a lesion of 

 the left hemisphere actually outnumber those in 

 which it has been caused by a lesion of the righl 

 (44, 141). Left-handedness, therefore, by no means 

 necessarily implies 'right-brainedness. 1 



These somewhat paradoxical findings have been 

 taken to indicate either that handedness and speech 

 laterality are essentially unrelated (44) or that cere- 

 bral dominance is less fully established in sinistrals 

 than in dextrals, aphasia being in consequence liable 

 to follow a lesion of either hemisphere (33, 57). In 

 keeping with the latter interpretation is the fact that 

 severe left-sided brain damage in early childhood 

 seldom significantly retards the development of speech 

 and that later removal of the damaged hemisphere is 



unlikely to provoke aphasia (5). Further, speech dis- 

 orders in children are as a rule more transient than 

 in adults and more liable to be provoked by damage 

 to either hemisphere (5). Taken together, the clinical 

 findings suggest some measure of equipotentiality of 

 the two hemispheres in relation to language and the 

 gradual establishment of a gradient of dominance in 

 the early years of life. At the same time, the precise 

 relation of handedness to dominance remains obscure 

 (12). 



Stuttering and Kind) ■ Defects 



It was for many years conventional to ascribe 

 stuttering and related defects to anomalies of cerebral 

 dominance and lack of unified speech control (91, 

 1321. In view of the bilateral central connections of 

 the speech organs, it appeared far from unreasonable 

 to postulate a single, functionally dominant, 'center' 

 in the control of articulate speech. This supraordinate 

 'center' was identified with Broca's area in the 

 dominant hemisphere. In support of this view might 

 be mentioned the comparative frequency of speech 

 disorders in left-handed individuals, in particular 

 those who have undergone an enforced "shift" of 

 handedness, and the evidence of widespread and 

 generalized disorganization of motor response in 

 man) stammerers (i ;.". At the same time, an ex- 

 planation along these lines is not without its difficul- 

 ties .Hid has recently fallen into disfavor. Xot all 

 sinistrals overt 01 •covert exhibit disorders of speech 

 and stuttering may occur in individuals without any 

 obvious sign of anomalous laterality. Further, emo- 

 tional difficulties have been implicated in many 

 stammerers, excessive anxiety, in particular, having 

 been repeatedly adduced as .1 causal factor (10, 20, 

 25, 51). It would therefore appear that the causation 

 of stuttering and kindled disorders ol speech is 

 multiple and unlikelv to find explanation in terms of 

 .1 single mechanism. None the less, there is much to be 

 said for Cobb's view of a 'supracortdcaT integrative 

 level in speech, disturbance of which may result both 

 from emotional factors and from lack of clear-cut 

 lateral dominance (26). 



Impressed by the importance of 'aural monitoring' 

 in speech control, Cherry and co-workers (22, 23) 

 have recentlv shown that the speech errors of some 

 stutterers can be suppressed by experimental inter- 

 ference with the feedback provided by the speaker's 

 perception of his own voice. Preliminary experiments 



