PHYSICAL MEASUREMENTS OF AUDITION 



171 



only 4,000 nerve cells in the basilar membrane with four or five fibre 

 hairs for each cell. Assuming that each hair fibre acts as a unit there 

 are still insufficient units for each perceivable tone and according to 

 the theory given above, a large number of these units must act at 

 one time. Consequently the ear must be able to interpret differences 

 in the intensity of excitation of each nerve cell as well as determine 

 the position of each nerve cell excited. 



Most modern neurologists believe in the "none or all" excitation 

 theory of nerve impulses. 59 " 60 They also claim that nerve impulses 

 can never be much more rapid than about 50 per second and cannot 

 therefore follow frequencies as high as those found in sound waves. 

 The second statement only emphasizes the necessity of assuming 

 that the intensity position as well as place position is necessary to 



2000 

 1 1800 

 j»I600 

 \l400 ■ 

 %I200 

 ^1000 

 \ 800 

 ^ 600 

 J 400 

 ^ 200 



.0001 001 01 .1 I. 10 100 1000 10000 p 



-80 -10-60-50-40-30-20 -10 10 20 30 40 50 60 10 60 a=AL 

 Values of Press u-° (p) or Loudness (a) 



Fig. 12 



account for the differentiation of pure tones. The first statement 

 is not necessarily in conflict with such an idea since anatomists are 

 not agreed upon the number of nerve fibres radiating from each 

 nerve cell. Since each nerve fibre can serve to give a unit nerve 

 impulse, the intensity of stimulation sent from a single nerve cell 

 can increase with stimulation depending upon the number of nerve 

 fibres brought into action. The intensity of the sensation produced 



