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Mr. C. S. Myers. The Influence, of 



head, it must stimulate the two ears with the same intensity. It is just 

 under these conditions that our localisation becomes erratic. As is well 

 known, a sound coining from in front is apt to be localised behind, and 

 vice versd. So, too, in regard to sounds placed before and behind the ear : a 

 sound produced midway between the front and the side of one ear is often 

 localised midway between the back and the side of that ear, and so on. 



It has been found that, although extremely erratic, our determination of 

 the incidence of a sound is capable of enormous improvement by practice, 

 and, seeing that our accuracy is greater with sounds richest in overtones,* 

 it has been supposed that our awareness of incidence is dependent on the 

 variations of timbre which occur with variations in the angle at which 

 the sound waves impinge on the auricle. 



Now, if it be true that variations in timbre are responsible for our 

 determination of the incidence of a sound, it should be possible to put this 

 assumption directly to the test by experimentally varying the timbre of a 

 given sound while its position is kept constant, and by observing what 

 changes, if any, in its apparent position are produced thereby. Such has 

 been the main purpose of the experiments described in this paper, 

 and, as will be seen, they afford a striking proof of the correctness of the 

 assumption. 



Two other possible factors affecting sound localisation have yet to be 

 mentioned. It has long been recognised that sounds coming from in front of 

 the subject's auricle are better heard than those coming from behind. The 

 auricle is so inclined and is so formed as to " catch " forward sounds better 

 than rear ones.f Such variations in loudness, according to the relative 

 positions of the sound and of the ear, may conceivably help in determining 

 the incidence of the sound. The other possible factor, assisting the 

 determination of laterality and incidence, consists in the tactual sensations 

 which vibrations of sound may conceivably evoke by their contact with the 

 auricle, the external meatus, or the tympanic membrane. The experiments 

 described in this paper also afford some estimate of the value to be attached 

 to these two factors. 



II. Experimental Methods, 

 The experiments were conducted in a sound-proof room (E, fig. 1), 

 the walls and ceiling of which, composed of stone, peat-moss, and cork 



* Angell and Fite, ' University of Chicago Decennial Publications,' vol. 3, part 2 

 (1902). 



t How the ear " catches " sounds is quite unknown. The old explanation of reflection 

 of the sounds from the concha to the tragus, and thence into the meatus, is untenable in 

 view of the disproportion between the size of the ear and the length of the sound waves. 



