146 BELL SYSTEM TECHNICAL JOURNAL 



pros and cons of various theories of hearing. These discussions have 

 been participated in by men from the various branches of science and 

 particularly by the psychologists, physiologists, otologists, and 

 physicists. During the past two or three years this discussion has 

 been particularly acute. It is not uncommon to pick up an article and 

 read in the beginning or concluding paragraphs statements such as 

 the Helmholtz theory of audition seems to have sunk beyond recov- 

 ery, 90 ' 65 f and at the same time an article written probably a month 

 later will have the conclusion that the Helmholtz theory of audition 

 is definitely established beyond all controversy. 70 " 75 



There is apparently a great deal of misunderstanding between 

 various writers because of different points of view due to different 

 training. To the physicist it seems that most of the discussions show 

 a profound ignorance of the dynamics of the transmission of sound 

 by the mechanism of the ear. Those discussions by the physicists 

 are frequently open to criticism by the otologist and psychologist, due 

 to his lack of knowledge of the structure of the ear or the mental 

 reaction involved in the process of interpretation. I think it is 

 fortunate that some of these scientists from the different branches 

 are now cooperating in their research work as is evinced by the ap- 

 pearance of several joint papers. (Papers by Dean and Bunch, 

 Minton and Wilson, Wegel and Fowler, Kranz and Pohlman, and 

 others.) 



It is not my purpose to discuss the merits of the various theories of 

 hearing, but I desire to present some of the facts of audition which 

 have been recently determined with considerable accuracy, and then 

 discuss the theory of hearing which best explains these facts. 



Hearing is one of the five senses. It is that sense that makes us 

 aware of the presence of physical disturbances called sound waves. 

 For my purpose, sounds may be classified into two groups, namely, 

 pure tones and complex sounds. A pure tone is specified psycho- 

 logically by two properties, namely, the pitch and the loudness. 

 These sensory properties are directly related to the physical properties, 

 frequency and intensity of vibration. Mixtures of pure tones of 

 different loudness, but of the same pitch, fall under the first class, 

 since such mixtures give rise to a pure tone. The complex sounds 

 are varying mixtures of pure tones. It will be noticed that phase has 

 not been taken into account. Except when using the two ears for 

 locating the direction of sources of sound, phase differences are not 

 ordinarily appreciated by the ear.* 



t These numbers refer to the bibliography at the end of the paper. 



