PHYSICAL MEASUREMENTS OF AUDITION 147 



These tones are usually transmitted by means of air waves through 

 the outer ear canal to the drum of the ear. From here the vibrations 

 are transmitted by means of the bones in the middle ear to the 

 mechanism of the inner ear. 



Those facts of audition which are familiar to almost everybody 

 are as follows: 



1. Pure tones are sensed by the ear and differentiated by means of 

 the properties pitch and loudness. 



2. When two notes, separated by a musical interval, are sounded 

 together, they are sensed as two separate notes. They would never 

 be taken for a tone having the intermediate pitch. In this respect, 

 hearing is radically different from seeing. When a red and a green 

 light are mixed together, the impression received by the eye is that 

 of yellow, an intermediate color between the two. 



3. There is a definite limiting difference in pitch that can just be 

 sensed. 1 " 9 



4. There is a definite limiting difference in intensity that can just 

 be sensed. 10 " 14 



5. There is a minimum intensity of sound below which there is no 

 sensation. 16 " 31 



6. There is an upper limit on the pitch scale above which no audi- 

 tory sensation is produced. 32 " 44 



7. There is a tower limit on the pitch scale below which there is no 

 auditory sensation produced. 45 " 51 



8. The ear perceives tones separated by an octave as being very 

 similar sensations. 



Another quality of audition which is not so commonly known was 

 pointed out by A. M. Mayer. 52 He stated that high tones can be com- 

 pletely masked by louder lower tones while intense higher tones can- 

 not obliterate lower ones though the latter are very weak. Experi- 

 ments to be described later in the paper show that this statement 

 must be modified somewhat. Very intense low ones will produce a 

 masking effect upon still lower tones, although the masking effect is 

 very much more pronounced in the opposite case. Many of the op- 

 ponents of the Helmholtz resonant theory of hearing claim that this 

 fact is fatal to such a theory. 52 



* This statement may require modification when more experimental data are 

 available. As shown later in the paper the middle ear has a non-linear response. 

 Consequently it would be expected that phase differences, especially between tones 

 which are harmonic, would produce spacial differences in nerve stimulation. 



