ILLUSTRATIONS OF AUDITORY SIGNALS 



207 



move from one ear to the other. If the 

 frequency was high when the tone seemed 

 to be in the left ear, and low when in the 

 right ear, then the left wing was high. The 

 opposite relation indicated that the right 

 wing was high. The amount of the bank 

 depended on the amount of frequency change 

 as the tone moved from left to right. Air- 

 speed indication was provided by introduc- 

 ing a short, fast "beep" into the tone. This 

 beep was actually a rapid frequency modula- 

 tion, and the rate of the beep depended on 

 airspeed. For each sweep of the tone from 

 ear to ear, the time was divided into two 

 parts. During the first part, a standard 

 beep rate was heard, and the second part 

 gave a beep rate which depended on airspeed. 

 The use of a standard rate had been shown 

 necessary in some of the earlier attempts 

 which we have not described here. This 

 type of signal was found to be reasonably 

 successful. 



Link Trainer Tests. Later tests on a Link 

 trainer showed that pilots could fly a fairly 

 straight course with these signals. The tests 

 also showed that pilots could learn to fly the 

 trainer with the auditory signals as fast as 

 with the visual indications. The described 

 signals were not necessarily the best possible 

 signals, but they were good enough to 

 demonstrate that the use of auditory signals 

 was entirely feasible. 



Conclusions from Flybar Experiments 



The Flybar experiments were not designed 

 to provide basic knowledge about the use 

 of auditory signals. They were the out- 

 growth of an attempt actually to develop 

 a set of signals for use in aircraft. Never- 

 theless they provided information about 

 some of the basic problems and requisities 

 of such signals. The following might be 

 considered the basic considerations for a 

 successful system of auditory signaling, in 

 submarines or elsewhere. 



1. The signal should sound real; i.e., it 

 should sound as nearly as possible like what 

 is actually happening. This is particularly 



true if the signal indicates motion or posi- 

 tion; it ought to sound like motion or posi- 

 tion. In other words, the signals should not 

 depend on a remote symbolism. Turn could 

 be indicated by the intensity of a monaural 

 tone, but such indication would be very 

 poor because it does not sound like what is 

 actually happening. 



2. Whenever more than one kind of in- 

 formation must be presented to an observer 

 simultaneously, the signals should be de- 

 signed to prevent listening to only one signal 

 at a time. In the Flybar experiments, this 

 was accomplished by combining all indica- 

 tions into one basic tone. 



3. Whenever directional or quantitative 

 information is to be indicated, some standard 

 signal must be provided to which the listener 

 compares the critical signal. Absolute psy- 

 chological standards are very poor, especially 

 in hearing. For example, in some of the 

 signals, airspeed was indicated by a "put- 

 put" which varied in rate much as a motor 

 sounds when it changes speed. But this 

 signal was usable only when some standard 

 "put-put" rate was provided. The ob- 

 servers could not remember what "normal" 

 speed was. Nor can they remember what 

 a "normal" intensity or frequency is. How- 

 ever, in spite of the fact that the absolute 

 pitch of a tone, or its intensity, cannot be 

 identified, it is an easy matter to tell that 

 one tone is louder than another, or that it is 

 higher in pitch. Thus, problems of direc- 

 tional and quantitative information all be- 

 come matters of auditory discrimination in 

 the usual academic sense of discriminating 

 one tone from another. 



Although the Flybar experiments demon- 

 strated that auditory signals are feasible 

 in a communication system calling for three 

 kinds of infoiTnation, it is questionable 

 whether the signals actually used were the 

 best signals. It would be very helpful to 

 have a program of further developmental 

 work on complex signals. If such signals 

 can be used on aircraft, there is little reason 

 why they cannot also be used successful! v 



