THE INFLUENCE OF INTENSITY RATIO ON BINAURAL 
SOUND LOCALIZATION. 
E. M. BERRY AND C. C. BUNCH. 
It has been recognized that the intensity ratio at the ears is 
a factor in the localization of sound, but it appears that its in- 
fluence has been greatly oyer-estimated. In the summer of 1916 
G. W. Stewart and 0. Hoy da did considerable qualitative work 
on this. Our present research is a continuation of their work 
with practically the same apparatus. 
The sound from a tuning fork of 256 d. y. is conducted by 
two tubes, one to each ear. One of the tubes is kept at a fixed 
distance from the fork, while the distance of the other tube from 
the fork can be varied. By using a Rayleigh disk the relative in- 
tensities of the sound at the binaurals can he found for any 
given position of the moveable tube. In this way known in- 
tensity ratios at the ears can be produced and their localization 
observed. Localization of this kind cannot be made very ac- 
curately; for the same intensity ratio there is generally a varia- 
tion of from 5° to 10°. G. W. Stewart and O. Hovda found that 
up to 45°, if they plotted the angular displacement from the front 
as the ordinate and the logarithm of the intensity ratio at the 
ears as the abscissa, the curve was a straight line ; or if © is the 
angle from the front, I R the intensity at the right ear and I at 
the left ear, 0=k log (I B /I, ). Our present work has been to 
see if this relation holds up to 90°. We have used two kinds 
of binaurals, those which are inserted in the ears or “closed” 
binaurals, and those which do not touch the ears or “open” 
binaurals. 
Our results when plotted in the same way have given straight 
lines; often, however, there are one or two breaks in the line. 
Our observations generally went from 30° left to 90° right. 
When there was one break it was generally in the neighborhood 
of 15° right with an increase of slope. When there was more 
than one break the second was close to 90° ; in any case after 90° 
had been reached a further increase of intensity ratio at the 
ears produced little or no effect and in most cases we did not 
use intensity ratios much greater than just sufficient to produce 
