280 



AUDITORY BIOPHYSICS 



contact with the cochlear fluid, compensating surface reinforcements. 

 The shading (Fig. VII-16) shows the thickened parts where the bone 

 structure possesses these reinforcements. 





Toet 



In 



? Anterior 



Heel *£ 



ii 



* Posterior ' 



Fig. VII-15. This graph shows the changes in potential at the apex of the cochlea 

 from data by Wiggers [1937]. The lower diagram shows the correlated positions 

 of the footplate proposed to account for the successive changes in potential observed 

 by Wiggers. 



Cochlear Microphonics 



That the compressional waves communicated by the moving footplate 

 to the vestibular fluid excite the aural membrane to set up an electric 

 potential, which may be detected in the acoustic nerve, was first dis- 

 covered by Wever and Bray [1930]. That the cochlea develops an inde- 

 pendent electrical potential synchronized with the pressure gradient 

 set up by the motion of the footplate was discovered by Saul and Davis 

 [1932]. 



Of special importance in the interpretation of the cochlear micro- 

 phonics is the discovery by Davis et al. [1934] that the inward movement 

 of the stapedial footplate created a positive change of potential and the 

 outward movement a negative potential at the cochlear apex. This dis- 

 covery led Wiggers [1937] to follow experimentally the changes in poten- 

 tial that took place at the apex of the cochlea as the motion of the foot- 

 plate slowly executed a complete cycle of positional changes. He found, 

 for example, that when the acoustic wave arrived at the eardrum the 

 stapedius muscle contracted. This contraction caused an outward 

 movement of the footplate, cocking the stapes for action. Fifty milli- 



