of Binaural Audition. 355 



the ears for a brief moment. Between this transient sound 

 and a real objective note tuned to beat with it, the author has 

 produced beats. He brought the tones to the ears with tubes, 

 one being intolerably loud, the other faint; and arrangements 

 were made by which a single movement opened one pipe and 

 closed the other at the same instant. Beats were heard for 

 about 1^ second after the cessation of the loud sound. 



An extremely curious case was mentioned to the author 

 some years ago by an eminent; acoustician. A person who 

 was afflicted with mumps on one side of the head heard all the 

 sounds in that ear raised about a semitone *, and heard beats 

 accompanying notes in the lower part of the scale. The author 

 inquired some time after of a non-scientific friend who had 

 suffered from a similar attack, whether any thing similar had 

 been noticed, but could only learn that voices and musical 

 notes jangled " like a harmonium out of tune." 



Effect of Fatigue upon Binaural Perception of Direction. 



5. While trying the above experiments on interference after 

 fatigue, the author noticed an acoustic illusion due to the same 

 origin. Let one ear be fatigued, as before, by listening to a 

 loud pure note. Then let the listener try to estimate the direc- 

 tion of a sound of the same pitch. If his left ear has been 

 fatigued, he will invariably imagine the source of sound to be 

 further to the right than it really is, and vice versa. The illu- 

 sory displacement in the direction of the sound is greater the 

 more complete the fatigue. When one ear was fatigued with 

 a c" fork no illusory displacement was perceived in an a" fork. 

 The author has, as yet, only tried these experiments in a 

 room, and with the almost simple tones of tuning-forks. The 

 observations are of interest, however, in the theory of Binaural 

 Audition. 



* In a discussion which followed the mention of this case, Professor 

 Michael Foster made the suggestion to the author that this abnormal 

 tuning-up of the receptive mechanism of the ear might be due to the ex- 

 istence of muscular tissues in the structures of the Corti organ. He 

 remarked that in the ligamentum spirale externum, outside the attachment 

 of the basilar membrane of the Corti organ, there may be seen, at least in 

 many specimens, cells which very closely resemble plain muscular Jibres 

 when examined in the microscope. If this be so, they could, apparently, 

 pull up the basilar membrane and tighten it. Professor Foster, who 

 kindly permits me to add this very interesting point, informs me that 

 while this view of these structures is taken by Todd, Bowman, and 

 Bottcher, their muscular nature is denied by Kolliker and Waldeyer. — 

 S. P. T. 



