SUPPOSE YOU WERE BLIND 



screen was being approached or not. After some practice 

 they could detect the screen at an average distance of 

 6.4 feet, only a little less than their average of 6.9 feet 

 when they were doing their own walking and listening. 

 Such a result would seem to dispel all doubts; surely no 

 one could argue now that anything but sound was in- 

 volved. But scientists who have studied problems like 

 this have learned to be extremely cautious. Many experi- 

 ments which have seemed this convincing have turned 

 out to be misleading. Suppose, for example, that the per- 

 son who walked up to the screen with the microphone 

 changed his breathing rhythm or the sounds of his foot- 

 steps and thus unconsciously conveyed to the remote 

 hstener his proxunity to the screen? This sort of uncon- 

 scious signaling has been known to occur, and, inciden- 

 tally, it accounts for many cases of what has been 

 interpreted as mental telepathy. 



This worry led to further experiments in which the 

 second person was replaced by a motor-driven cart 

 which carried the microphone towards the screen. The 

 subject in the soundproof room controlled the move- 

 ments of the cart while Ustening to the sounds the mi- 

 crophone picked up. As often happens in a scientific 

 experiment, new facts raise new questions— one often 

 ends up with more questions than he had at the begin- 

 ning. Here the question raised was of major importance. 

 Granted that sounds could be conveyed over the tele- 

 phone system, what were the actual sounds that told 

 the listener the screen was near? In the original experi- 

 ment no special effort was made to generate sounds or 

 produce echoes; indeed, the experimenters in the begin- 

 ning had been uncertain that sounds were really of any 

 consequence. They had simply tried to bring phenome- 

 non into the laboratory and arrange conditions under 

 which it could be repeatedly studied. But having learned 



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