NUMERICAL CONSTANTS OF SPTrCII .(A7) HEARING 377 



p. 28i>. Sopt.. 1023.) The sonsalimi l,\tt S of a smind is (litincd I)y 



p 

 5 = 20 loK where P„ i.s the tlireshold pressure, or it is llu- miniher 



of sensation units al)o\e the tlireshold of audil>iiil>-. Tliese sensation 

 units are the s.iine as the transmission units used in tele|)lione ea- 

 Kineerinn- 



The per cent increase in fretiucncy to lie just perce()lil)Ic varies with 

 sensation level in about the same way as does the per cent increase in 

 intensity to be just perceplil)le. The values arc for monaural re- 

 ception the tones beinjj heard successively. 



\I. TiiK \imhi:r of Doriu.R \ihr.\ti()\s Nfxess.arv to 

 DetivRmine Pitch 



(Bode, Psychol. Stud.. 2. p. -JU:}, l'.l()7) 

 T.XHI.K II 



\1I. The Masking Effect of One Sound J^pon the .AuniBiLiTY 

 OF .Another Sound 



(Wegel and Lane, Phys. Rrc. 2:i, p. 2fi6. Feb., 1924) 



If the ear is stimulated by a pure tone of frequency Ni, it is in 

 general rendered less sensitive to other pure tones. The tone that 

 constantly stimulates the ear is called the masking tone. The tone 

 that is heard in the presence of this stimulating tone is called the 

 masked tone. The masking is measured in sensation units or TU's. 

 It is equal to 20 X login of the ratio of the pressures necessary to per- 

 ceive the masked tone with and without the presence of the masking 

 tone. In other words it is equal to the number of units that the 

 threshold has been shifted. Fig. 2 shows the amount of masking 

 (ordinate) of tones of various frequencies as a function of the sensa- 



