1720 



11 \M)B( ic IK OF 1-IIYSH il 1 «, Y 



NEI'ROI'IIYSIOI.OCY III 



indicate that, it a loud tone is applied through head- 

 phones to the ears of the subject, thus effectively pre- 

 venting perception of his own speech sounds, a con- 

 siderable reduction in stammer is achieved. A similar 

 result is also claimed if the subject is merely required 

 to 'shadow' lii-. repeat concurrently! a message read 

 bv ,1 normal speaker. Although these findings stand 

 in need of confirmation, they at least create the pre- 

 sumption that some forms of stammering arise on a 

 perceptual rather than an executive basis. This might 

 sim'gesi .1 fresh approach to the elucidation and ther- 

 .ipv of the 'functional' speech disorders. 



Development oj Speei h 



In the acquisition of speech, it would appear that 

 the infant's perception of his own speech sounds plays 

 a most important part in governing motor develop- 

 ment. Indeed "circular reactions' are readily set up 

 in which a speech sound, once spoken, initiates its 

 own repetition. This process no doubt provides the 



basis lor imitation and repetition of the speech of 

 others. The ear-voice 'feed-back loop' would appear 

 of the utmost importance in the monitoring of speech 

 and in prov iding the basis of orderly speech develop- 

 ment. In the adult, it has been suggested that volun- 

 tary control of the voice in singing or speaking at a 

 predetermined rate is linked with the activity of the 

 motor area as integrated with .1 frequency factor of 

 unknown nature provided by the auditory corn \ 

 (61). At all events, speech control may readily be 

 envisaged in terms of a whole series of 'feed-back 

 loops," integrated at various levels and providing the 

 general basis of control of the speed, tempo and 

 rhythm of speech 174). At the highest levels, these 

 reactions are further integrated with processes of 

 symbolic formulation and expression, the nature of 

 which still eludes physiological analysis. But it may 

 be said with complete confidence that the 'language 

 areas' of the dominant cerebral hemisphere comprise 

 the essential machinery of human thought and 

 speech. 



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