SUPPOSE YOU WERE BLIND 



tinguish between a sound source that is straight ahead 

 and one that is displaced only 10° to one side. If the 

 source is 3 meters away, the 10° displacement which is 

 clearly noticeable involves a difference in time of arrival 

 at our two ears of about 0.1 millisecond. It is difficult 



Fig. 15. Your ability to discriminate minute differ- 

 ences in the time of arrival of two sounds can be 

 tested with this device. Any source of sharp clicks will 

 do if it is tightly enclosed in the box so that you hear 

 it only through the tubes. 



to locate sound sources accurately if they he directly in 

 front of us, or anywhere in the plane that is equidistant 

 from the two ears. If we have to attempt this, we usually 

 do so by moving our heads about and bringing one ear 

 closer to the source. 



The role of differences in time of arrival of a click at 



141 



