BINAURAL LOCATION OF COMPLEX SOUNDS 37 



pure tone follows directly from the absence of other frequencies with 

 which the pure tone may be compared. 



As we are here concerned with binaural phenomena we shall con- 

 fine our attention to the relative phases and intensities at the two ears. 

 The question at once arises: does the observer actually hear the differ- 

 ent tones separately, and if so, does he assign a location to each 

 separately? 



To what extent the listener locates each component separately 

 depends upon the ease with which the tones can be distinguished. 

 The experiments which bear most directly upon this point are those 

 in which the component tones at the two ears are arbitrarily adjusted 

 to give values of phase difference corresponding to different locations. 

 This is done under conditions where the location of each component 

 separately is largely determined by the phase difference. More ^ 

 experimented with two tones, transmitting them to the ears through 

 tubes of adjustable lengths. This permitted him to change the phase 

 difference at the two ears while keeping the intensities substantially 

 equal. He observed the apparent location for various settings when 

 each tone was applied by itself and when both were applied together, 

 using forks of 256 and 320 cycles. With the paths equal the tones 

 combined into a chord located in the median plane and the separate 

 components could not be heard. With a setting for which the two 

 components separately appeared on opposite sides of the head, one 

 component was heard distinctly by the right ear only on the right 

 side, and the other by the left ear only on the left side. At the same 

 time the chord was heard rather indistinctly near the median plane 

 but tending slightly toward the side of the lower tone. 



Apparently the observer does not consciously separate the chord 

 into its components unless he is forced to do so by some inordinate 

 discrepancy between the positions of the images formed from them. 

 There is no evidence in the case of equal paths to show that he did 

 or did not subsconsciously locate the separate components and find 

 them to be in agreement. In view of the second experiment it seems 

 probable that he did. In this latter experiment he obviously found 

 that the two components corresponded to different locations and 

 assigned different sources to each. At the same time his experience 

 told him that tones which would combine to form a musical sound 

 generally have a common source. Hence he may have concluded 

 subconsciously that the sound waves had probably been distorted 

 in coming from a common source and so he corrected his observations 

 * Louis T. More: Phil. Mag. XVIII, 1909, p. 308. 



