ECHOES OF BATS AND MEN 



This was probably due to the reduction in sound level 

 caused by the shielding effect of the bulky hood. 



Guiding Echoes 



These experiments would seem to have settled the 

 matter once and for all, but criticisms would still have 

 been possible if the experimenters had stopped at this 

 point. Perhaps the pressure of the ear covering was dis- 

 turbing some subtle tactile sense. Perhaps blind men 

 were warned of obstacles not by hearing as such but by 

 some special kind of pressure sense involving the ear 

 canal or adjacent areas of skin. Even men who had stud- 

 ied this subject for years were skeptical that sound waves 

 could be the messengers by which blind people detected 

 obstacles. Further, many blind men themselves still con- 

 tinued to think they felt obstacles. To convince such 

 skeptics it was necessary to modify the experiment so 

 that sound and only sound carried the necessary infor- 

 mation from the outside world into the subject's nervous 

 system. This might seem a hopeless task; if the experi- 

 ments described above were unconvincing, what argu- 

 ments could hope to overcome such skepticism? 



The answer was to employ a telephone system to 

 transmit the appropriate sounds to the subject sitting in 

 a remote and soundproof room. The sounds transmitted 

 over the telephone wires were those picked up by a mi- 

 crophone carried by a man walking along the same 

 obstacle course. They were similar, though not identical, 

 to what the man would hear himself if he were listening 

 for evidence that the screen was just ahead. 



The results of the telephone experiment were aston- 

 ishingly close to those obtained by the same subjects in 

 the original tests. They could sit in the soundproof room 

 and decide by listening to the telephone whether the 



136 



