SUPPOSE YOU WERE BLIND 



soundproof room. The distance of first detection aver- 

 aged 3.75 feet, less than the range of detection when in 

 an earlier test a person carried the microphone toward 

 the screen. Nevertheless, it was an impressive perform- 

 ance, considering how greatly the situation had been al- 

 tered from the first series of experiments. Other sounds 

 were also tried, but the experim.ents were concluded be- 

 fore the ideal sound had been discovered which men 

 might use to obtain the more revealing echoes. The in- 

 vestigations ended because the original problem had 

 been conclusively solved by the proof that sounds and, 

 in particular, echoes were the messages that inform blind 

 men about the existence and position of obstacles. 



One significant feature of this important discovery is 

 the striking divergence between the subjective feelings of 

 many blind people and all the objective evidence which 

 we have examined. When a man has developed the re- 

 markable abihty to find his way about through the bus- 

 tling traffic of a modern city in what to him is total 

 darkness, and when he does this so skillfully and un- 

 obtrusively that one can travel with him for hours and 

 never suspect that he is blind, then it is natural to assume 

 that he knows what he is doing and how he does it. But 

 often the expert blind man can say only that he some- 

 how "feels" his way and "knows" before he bumps into 

 the tree or fence post that it is there. If questioned more 

 closely, he may say he feels the proximity of the object 

 with his hands, his face, or his forehead. Yet when the 

 process of obstacle detection is studied under controlled 

 conditions, it is clear that sounds and hearing are the 

 essential ingredients. In addition, the whole surface of 

 the blind man's skin can be covered by heavy felt or 

 leather without preventing him. from detecting obstacles 

 before he strikes them. When his ears are plugged, he 

 no longer "feels" the obstacles with his hands or face, 



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