SUMMARY 



215 



When the comparison tone has a loudness of 

 2000 miUisones we will arbitrarily give it a 

 value of plus five. Now, should plus ten 

 be represented by 4000 or 3000 millisones? 

 In the former case, the plus 10 value is twice 

 that of the plus five value; in the latter case 

 the difference between standard and compar- 

 ison is twice as great. In other words, even 

 though we assume that the present loudness 

 scale can predict what these quantities are 

 for a particular intensity, we still do not 

 know which kind of scale is more meaningful 

 in a communications situation. 



Auditory Counting 



One other area of research which could 

 provide useful information for signalling sys- 

 tems is that concerned with the counting of 

 a series of tones or impulses. How fast can 

 a series of tones be repeated if the listener is 

 expected to get an accurate count of the total 

 number? Can number patterns be learned, 

 even though accurate counts are not pos- 

 sible? With a limited kind of information, 

 and a limited quantitative scale, very ac- 

 curate information could be transmitted 

 automatically with series of impulses or 

 tones. We need to know how well this type 

 of signal can be used, but there is no infor- 

 mation available at present. 



The Psychomotor Problem 



Throughout this discussion we have talked 

 almost entirely about the purely perceptual 

 problems. We have been concerned with 

 what can be heard. In the main, these are 

 the really important and basic problems, but 

 they are not the only problems. 



Motor Coordination 



The problem of auditory signalhng is bas- 

 ically a psychomotor problem, at least in 

 most situations. The auditory signal is pro- 

 vided because somebody is supposed to take 

 some action. In both radio range and Fly- 

 bar operation, for example, a continuous 

 motor adjustment is required as a result of 



the information received from the auditory 

 signal. 



The problems of audio-motor coordination 

 of this kind have been investigated very 

 little. A program of research analogous to 

 the work done on visual-motor perfonnance 

 is necessary. There is, for example, a con- 

 siderable body of research on eye-hand co- 

 ordination, but practically none on ear-hand 

 coordination. 



Audio-Visual Comparisons 



One of the best reasons for wanting audi- 

 tory signals is that the eyes are asked to do 

 more and more work in many of our highly 

 complex modern equipments. Some inter- 

 sensory comparisons are necessary to deter- 

 mine just what type of situation can be 

 handled best with auditory signals. In 

 many cases such research w^ould almost be- 

 come a study of the breakdown of the visual 

 perception process, but they would be useful 

 to tell us when auditory signals could be most 

 valuable. 



As an illustration of this kind of problem, 

 one typical experiment might be concerned 

 with measuring the precision of an eye-hand 

 coordination involving two movements in 

 response to information provided from two 

 dials or meters. As these dials are moved 

 farther and farther apart what happens to 

 the coordination? At what distance can the 

 operator no longer follow both meters? 

 Similar comparisons would be made with one 

 and two auditory signals, either alone or in 

 conjunction with one visual signal. 



Summary 



Auditory signals are a form of display, 

 but are usually characterized by being dis- 

 crete in time, and some action is assum.ed 

 on receipt of the information. Whenever 

 a communications situation is concerned 

 with a limited kind of information, an audi- 

 tory signal can be used to provide a fast 

 indicator of what to do. They are likewise 

 useful as a substitute for visual displays 

 when the visual load on an operator becomes 



