THE PERCEPTIO.'N OF BINAURAL PHASE DIFFER- 
ENCE NOT CAUSED BY AN INTENSITY EFFECT 
G. W. STEWART 
ABSTRACT 
It is becoming well known that it is possible to perceive a differ- 
ence in phase at the ears by a displacement of the phantom 
image from the median plane. Attempts have been made to ex- 
plain this effect by bone conduction and the effect of intensity,^ 
for it is also well known that a difference of intensity will also 
cause a displacement. But the only published explanation of 
this character has been shown to be not satisfactory. Yet, since 
a large group of psychologists believe that sensation depends en- 
tirely upon the mode of response of the end organ and not upon 
the character of the stimulus, it is difficult to secure convincing 
evidence that The character of the stimulus, i.e., phase, does 
produce an apparent displacement of the phantom source. 
If, however, it can be demonstrated that intensity does not in- 
directly produce the effect of phase, there remains but one con- 
clusion, i.e., that there is direct perception of phase difference. 
Such a proof has been found provided one accepts an obvious 
proposition, e.g., that if, , for a given frequency, the observer 
does not respond to a difference of intensity at the ears by a dis- 
placement of the phantom sound, then intensity cannot, by bone 
conduction and consequent variation of intensity at one ear by 
variation of phase externally, produce such a displacement of the 
phantom sound. 
In the test of five individuals for the intensity effect and the 
phase effect, three of the five are found to have the phase clearly 
defined in the region of frequency when the intensity effect does 
not exist at all. Indeed, the phase effect is just as clearly defined 
at a frequency where the intensity effect exists as at a fre- 
quency where the intensity does not exist. This would seem to be 
convincing evidence that the phase effect cannot be explained by 
terms of intensity. 
Physical Laboratory, 
State: University or Iowa. 
