254 



VISUAL COMMUOTCATION 



systems carry only a few well defined mes- 

 sages whose content has been carefully se- 

 lected for intelligibility against a noise back- 

 ground, for precision, and for the avoidance 

 of sounds which are similar to one another, 

 communication becomes quicker and more 

 accurate, and the difficulties placed upon the 

 system by the span of apprehension and of 

 immediate memory tend to evaporate. 



Minimal Need for Training 



In general, owing to our well-established 

 speech habits, auditory systems require far 

 less training of both sender and receiver 

 than do visual systems. Voice requires a 

 minimum of training. Systems which do 

 not utilize speech, and which are extremely 

 versatile in the variety of messages w^hich 

 they can carry require relatively long train- 

 ing, whether auditory or visual. The stud- 

 ies of Keller and his associates (5) on radio 

 code transmission during the recent war 

 showed that such training involves two com- 

 plex processes. 



1. Differentiation of response. The sender 

 must learn to give accurately and rapidly 

 a variety of extremely complex sequences 

 of responses, which are sharply differentiated 

 from each other and from any other similar 

 responses he might make. The radio code 

 sender must learn to transmit words by a 

 complicated and specific pattern of muscular 

 activities, which have the effect of closing 

 an electrical circuit to produce a temporal 

 patterning of electrical impulses. 



2. The receiver, on the other hand, must 

 develop a sensory discrimination. He must 

 learn to respond differentially among a great 

 variety of complex stimuli which closely re- 

 semble one another. 



Both processes are basic to the develop- 

 ment of versatile communication systems 

 which do not use speech. The necessity 

 of establishing differentiation among re- 

 sponses and discriminations among stimuli, 

 again emphasizes the need for necessary mes- 

 sages to be analyzed with the view of re- 

 ducing the number of symbols which must 



be employed in a communication system. 

 As each new response of the sender is added, 

 the difficulty of establishing differentiation 

 and discrimination increases; the time re- 

 quired for training is an exponential function 

 of the number of different discriminations 

 and differentiations which must be made. 

 This suggests strongly that if modifica- 

 tions in naval communication systems are 

 made, they should make use of already es- 

 tablished habits of discrimination and re- 

 sponse, so far as possible. Systems which 

 represent further developments of already 

 existing systems should be sought. 



With these criteria, it becomes possible 

 to enumerate some of the difficulties of tran- 

 sient auditory communications that suggest 

 that the feasibility of visual systems be in- 

 vestigated as possible complements or sub- 

 stitutes for existing auditory systems. 



Some Remarks on Systems 



Two limitations of auditory communica- 

 tion systems stand out as most significant. 

 The first of these is the presence, in many 

 situations in which accurate communication 

 is necessary, of masking noise at intensity 

 levels so high that the individual is not able 

 to discriminate the message from the mask- 

 ing background noise against which it ap- 

 pears. In submarines, the ambient noise 

 may reach and remain at levels of 80^ or 

 100 decibels (6). 



The second limitation is that auditory 

 systems depend greatly for their efficiency 

 upon the intelligence and training of the 

 receiver. He must comprehend the mes- 

 sage, and retain it, prior to his response. 

 If information or commands are received 

 but misunderstood, or if they are forgotten 

 before action has been taken, unfortunate 

 consequences may ensue. The ''Aye, aye" 

 or "Very good" of a simple acknowledge- 

 ment may obscure failure to understand or 

 remember. Auditory communication, then, 

 places great demands not only on auditory 



* Harris, J. D. Personal communication. 



