Chapter VII 



AUDITORY BIOPHYSICS 



In a physical sense, sound is a disturbance of a vibratory nature in an 

 elastic medium. The disturbance may or may not be audible to a 

 human ear. An auditory sensation may be produced by such a physical 

 disturbance provided that its frequency lies within the response range of 

 the auditory mechanism and its energy is sufficiently great to affect this 

 mechanism sensibly. 



The quantitative study of the vibrating disturbance lies academically 

 in the province of the physicist. The analysis of the structure of the 

 human response mechanism lies in the province of the anatomist. Its 

 functional aspects are taken over by the physiologist; the psychologist 

 more often than not will consider whatever is left untouched by the above 

 specialists as his field of interest, especially the characteristics of sound 

 as consciously heard or experienced. 



The biophysical aspect merges all these provinces, deals with the 

 effects of the external vibratory disturbances and the structure of the 

 auditory mechanism, and analyzes the response characteristics of the 

 structure in terms of fundamental physical laws. 



The interest in biophysics is therefore in both aspects of sound: 

 (1) the purely mechanical actions of the body producing the vibratory 

 disturbances, the property of the elastic medium which transmits the 

 vibrations to the eardrum and by way of the ossicles to the fluids of the 

 inner ear; and (2) the bioelectrical response to the mechanical processes 

 which are essential to the complex experience called hearing. 



The Overall Aspect of the Auditory Process 



The essential requirement for the auditory process is a vibrating object 

 immersed in a medium, normal air under standard conditions, which 

 may be called the object space. The vibrating object must be able to 

 communicate its vibrations to the medium of the object space. The 

 aural mechanism immersed in the object space must be able to transmit 

 the objective phenomena to the cochlea, after which it is subjectively 

 experienced as sound having attributes of loudness, pitch, and quality. 



The mechanism making this transfer is composed of the external canal 

 leading to the eardrum, an interlocking set of three bones, two muscles, a 



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