ILLUSTRATIONS OF AUDITORY SIGNALS 



203 



of a signal. Directional information re- 

 quires differential sensivity of the greater- 

 than or less-than type. 



Quantitative Information. A still more 

 precise kind of information requires not only 

 identification of direction, but also of 

 amount. Here, of course, we get into all 

 the problems of psychological scaling. If 

 we want to provide automatic transmission 

 of information to a fire-control radar opera- 

 tor, then we must be able to tell the operator 

 exactly where to position his director. It 

 is not enough to provide simple directional 

 information — at least, if we want a reason- 

 ably fast response on his part. Simple di- 

 rectional information can be used if the 

 operator moves the director in the stated 

 direction at a constant speed until the signal 

 tells him that he is now "on." Lack of 

 quantitative information, however, makes it 

 impossible for the director operator to adjust 

 his speed of movement to the amount by 

 which he is off the target, so that he can 

 move rapidly for large misadjustments, and 

 slowly for small ones. 



We could, of course, have combinations 

 of various kinds of information in one tonal 

 signaling system. The more we combine 

 different kinds of information into one audi- 

 tory system, the greater the psychological 

 problems become. In fact, one of the most 

 important psychological problems in this 

 area is the determination of the usefulness 

 of tonal signals. How many different kinds 

 of information can be provided with tones? 

 What characteristics of tones make it easy 

 for them to be ignored, and what characteris- 

 tics make one signal stand out against other 

 signals? We know very little about the 

 answers to questions such as these. 



In considering, or designing, a tonal signal- 

 ing system, it is important to know precisely 

 what kind of information is required. A 

 good general principle, not only in auditory 

 signals, but in all displays, is never to provide 

 more information than is needed or can be 

 used. Too much infomiation only confuses 

 the listener, and slows him down in using 



the signaling system. Also, the more infor- 

 mation provided, the more difi&cult are the 

 discriminations required. 



Illustrations of Auditory Signals 



Auditory signals, other than speech, can 

 be classed roughly into two groups. The 

 first of these we will call occasional signals. 

 They are signals for which no special com- 

 munications system is set up, but which 

 occur for anybody to hear who happens to 

 be present. These signals do not provide 

 at all a continuous source of information, for 

 they occur only on some specific event. The 

 alarm of a clock, the siren of the fire engine, 

 the factory whistle, are all occasional signals. 

 This type of signal is not much of a problem, 

 since about the only requisite is audibility. 

 Problems of discrim inability rarely occur. 



The other class of signals involves a speci- 

 fic communication system which provides 

 a continuous source of information, although 

 not necessarily a continuous transmission 

 of information. Such signals are less of a 

 display, in the sense that they do not provide 

 information which may be used by anyone 

 who happens to hear them. The continuous 

 signals are usually there because it is ex- 

 pected that some action will occur as a 

 result of them. These signals are specific 

 to a particular series or group of related 

 actions. 



There are not many continuous signals 

 in use, although it is quite probable that they 

 could be used much more than they actually 

 are at present. We shall discuss some of 

 the work done on two types of auditory 

 signal — the radio range and Flyhar — as illus- 

 trations of research which is specific to prob- 

 lems of auditory signaling. These two types 

 of signals are, of course, not used on sub- 

 marines. However, if research is under- 

 taken on the possibility of using tonal signals 

 on submarines, the program of exploration 

 and of testing would presumably follow the 

 lines of the research programs undertaken 

 with these two signals. 



