ECHOES OF BATS AND MEN 



organs detect and interpret this information from the 

 outside world. From about 1890 to 1940 many studies 

 were made of the "sense of obstacles," but only in the 

 early 1940s was a conclusive answer obtained from care- 

 fully controlled experiments. While these experiments 

 were performed by men who called themselves psycholo- 

 gists, the experiments can be considered classic examples 

 of biophysics, the application to problems posed by liv- 

 ing organisms of the same basic principles of investiga- 

 tion that have developed physics as a rigorous science. 

 The chief difference between biophysics, thus broadly 

 defined, and the physics of non-living systems is the 

 greater degree of complexity and refinement of living 

 organisms. Animals and men are made of far more 

 intricate mechanisms than clickers and ripple tanks, mi- 

 croscopes or television sets, and this is why our under- 

 standing of biological processes is so much less thor- 

 ough and complete than our knowledge of physics or 

 chemistry. 



The psychologists, or biophysicists, who finally solved 

 the question of obstacle perception by the blind were 

 Professor Karl M. Dallenbach of Cornell University, and 

 two graduate students, one of whom, Michael Supa, was 

 himself totally blind. Milton Cotzin, the other student, 

 had normal vision, but he and others who served as ex- 

 perimental subjects wore blindfolds for many hours at a 

 time in order to experience what life is Hke for the blind, 

 and, in particular, to develop as much as possible the 

 ability to detect obstacles before bumping into them. 

 First the experimenters set up a sort of obstacle course, 

 a long hallway down which the subject walked and across 

 which was placed a large screen of fiberboard at some 

 point chosen by the experimenter. This location was var- 

 ied from trial to trial, so that the subject never knew 

 whether it was 6, 10, 18, 24, or 30 feet ahead of the 



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