NATURE OF LANGUAGE JONES 497 



mind, it has been proposed to measure pitch sensation on a scale 

 such that the pitch of a tone will be given by one hundred times 

 the logarithm to the base two oi: the pitch number or frequency. 

 These sensation scales of loudness and pitch are given on Figure 4 in 

 addition to the physical scales of energy and frequency. From the 

 observations made on intensity and pitch discrimination, it is pos- 

 sible to show that approximately three hundred thousand different 

 pure tones are separately distinguishable by the average ear. The 

 number of complex sounds which can be sensed is even much greater. 



The nonlinearity of operation of the ear gives rise to a number 

 of interesting hearing phenomena. When a simple tone is made 

 very intense the vibratory efficiency of the middle ear and cochlea 

 are no longer constant. This gives rise to harmonics which cause 

 the basilar membrane to vibrate in other zones than that charac- 

 teristic of the fundamental. If a second intense tone of another 

 pitch is now impressed, its harmonics are also introduced. Under 

 some conditions combination tones appear having frequencies which 

 are the sums or differences of the fundamentals or harmonics. 

 Some of the combination tones may take the form of beats. Such 

 harmonics, combination tones, and beats are purely subjective effects 

 brought in by the departure from linearity of the vibratory mecha- 

 nism of the internal ear. 



The masking of one tone by another is a second effect of interest. 

 An intense low tone is observed to mask or obscure weaker, high 

 tones ; but high tones, even though intense, have scarcely any mask- 

 ing effect on lower ones. The explanation offered for this is that the 

 intense low tone, with its subjective harmonics, sets up vibrations in 

 the basilar membrane which extend along the membrane to a con- 

 siderable distance from the base of the cochlea so that vibrations of 

 higher frequencies which might otherwise obtain in the adjacent 

 region, are interfered with. With the opposite state of aft'airs, the 

 high-pitched vibrations extend only a short distance from the base, 

 and more remote portions of the m.embrane are free to sense tones 

 of lower pitch. 



It will readily be apprehended that with complex tones com- 

 plicated effects may be obtained. Wl^en such a tone is made very 

 loud, as by amplification, its tone quality may be greatly altered 

 even though its composition is in no-wise changed. In general its 

 low frequency components will appear more prominent and its 

 higher frequencies diminished. 



Referring again to Figure 4, the area of sensation most used in 

 conversation is represented approximately by the shaded area of 

 the figure. The more intense vowel-like sounds account for the 

 upper part of the shaded region, while the weaker consonants 

 accoimt for the most part for the shaded regions of lower intensity 



