Chapter 1 



HOW WE SEE: A SUMMARY OF BASIC PRINCIPLES 



A. CHAPANIS 

 The Johns Hopkins University 



General Introduction 



The seven chapters which comprise this 

 section on Visual Problems discuss ex- 

 periments and sets of visual data which 

 should assist the naval engineer, scientist 

 and tactician in designing machines and 

 operations to use the eyes more effectively. 



The chapters which follow this one deal 

 with reasonably specific applied problems. 

 The present chapter serves both to orient 

 the reader with respect to certain general 

 problems of visual research and to provide a 

 background of visual information to which 

 ensuing chapters will refer and upon which 

 they will build. In particular, this chapter 

 deals briefly with units and methods of 

 measurement in visual science, and then in 

 more detail with a description of certain 

 visual processes and functions which enter 

 into all specific tasks from map or dial 

 reading to visual search. 



Although the scientific literature on 

 vision is enormous, the engineer or apphed 

 visual scientist who attempts to put this 

 information to practical use soon discovers 

 that there are rather conspicuous gaps 

 in our knowledge. He observes gaps not 

 only in many areas of applied research but 

 also in our basic research information 

 about vision. Such data as he does find 

 are often deficient because of two major 

 faults which characterize many of our 

 visual studies: they have been done to 

 satisfy just one or two theoretical points, 

 and they have used but few subjects. 

 As regards the first point, the laboratory 

 scientist appears particularly loath to repeat 

 the work of his colleagues. Once the 

 general nature of some visual function is 



known, his interest in that particular 

 problem, as a problem for research, is over. 

 The applied visual scientist therefore must 

 frequently be content with data in which 

 important parameters have been incom- 

 pletely studied, or which can be put to use 

 only by making questionable assumptions. 



The second kind of deficiency is also 

 serious, because the solution to a practical 

 problem often requires information about 

 the visual characteristics of the average 

 person. In addition to questions of reliabil- 

 ity which can be raised about experiments 

 done on small samples of people, many 

 visual studies are open to the criticism that 

 they have been made on biased samples — on 

 subjects purposely selected to have excellent 

 visual acuity, no visual defects, etc. Sam- 

 ples of such individuals are hardly repre- 

 sentative of people in general, or even of 

 servicemen in general. This means that 

 the repetition of many studies, although not 

 as stimulating as the exploration of new 

 problems, is definitely needed to provide the 

 practical scientist with better normative 

 data. 



As the well-established, useful facts about 

 vision are reviewed in this and the following 

 chapters, numerous examples of research 

 needs will be pointed out and discussed. 

 It is hoped that they may stimulate investi- 

 gations on what the writers believe are 

 fruitful problems. 



The Nature and Measurement of 

 Visual Stimuli 



Visible Radiant Energy 



The radiant energy to which our eyes are 

 sensitive is composed of electromagnetic 



