INTERIOK COMMUNICATION BY INSTRUMENT DISPLAY 



265 



Analysis of necessary communications 

 should reveal, first, the stations between 

 which messages must be transmitted; sec- 

 ond, the minimal content of such messages; 

 and finally, the frequency with which these 

 minimal messages are transmitted. It is the 

 necessary messages which are most fre- 

 quently repeated with systematic changes 

 only (e.g., ''Bridge to maneuvering room: 

 make seven five turns") which lend them- 

 selves to visual communication systems. 



Such traffic analysis defines the feasible 

 for the designer of the visual system. It 

 yields the total number of different messages 

 which the visual communication system be- 

 tween two particular stations must carry, 

 and so determines the complexity of the 

 visual display by instrument which must be 

 produced at the stations. It also yields the 

 number of symbols that both the sender and 

 the receiver must learn. With the problem 

 so defined, the psychologist is able to decide 

 the specific types of stimuli which must be 

 employed in investigations to determine the 

 display most efficient psychologically, i.e., 

 the display which requires least training of 

 sender and receiver and at the same time 

 yields maximum accuracy and speed of re- 

 sponse by the receiver. To the engineers 

 goes the parallel problem of designing relia- 

 ble multiple-channel circuits for the activa- 

 tion of visual displays. 



Specifically, how might visual communi- 

 cation by instrument work, and what advan- 

 tages might such systems have, as supple- 

 ments to present voice communications, or 

 as substitutes in the event of breakdown or 

 excessive masking? The systems envisaged 

 would utilize signal lights of varying proper- 

 ties — e.g., dial displays and even, in some 

 instances, perhaps actual words — the exact 

 form taken by the visual displays being de- 

 pendent upon experimental findings. The 

 stations on such a hypothetical circuit would 

 have identical display boards and message- 

 input equipment, so that each message could 

 be repeated back to the sender. Messages 

 put into the system would also be displayed 

 on all boards until taken off by the receiver 



to indicate that appropriate action has been 

 taken. In use, the system should have cer- 

 tain clear-cut advantages, which may be 

 enumerated as follows. 



1. Such instrument communication can 

 proceed without disturbance by noise. In- 

 deed, it can be disturbed only by electrical 

 breakdowns. 



2. The visual symbols employed may be 

 made to persist through a period of time 

 great enough so that the immediate memory 

 span and the span of apprehension do not 

 limit the receiver's accuracy as drastically 

 as they do in auditory communication. The 

 complex messages which may be presented to 

 the receiver by the display panel may remain 

 there sufficiently long for two types of ac- 

 knowledgment, both of which will ensure 

 that immediate and proper response is made 

 and that the sender is advised of the action 

 taken. The first acknowledgment is a re- 

 turn signal repeating the message back to 

 the sender. The second acknowledgment, 

 executed either when the receiver is begin- 

 ning to act on the instructions of the mes- 

 sage, or when action is complete, entails the 

 wiping clear of the displays of the communi- 

 cation system. This makes possible the in- 

 stantaneous evaluation of the situation by 

 the sender at all times. Finally, the persist- 

 ence of the visual stimulus provides sufficient 

 time for the accurate logging of the message, 

 if this is desired. 



3. Such visual communication is simple, 

 because it is designed to be so. A prelimi- 

 nary survey of circuits ensures that the sys- 

 tem carries only a set number of well-known 

 messages, so that the number of stimuli 

 which must be discriminated is few. This 

 simplicity and designed inflexibility should 

 guarantee that the only communications car- 

 ried are those for which the circuit is installed 

 and that the problem of circuit discipline is 

 virtually eliminated. 



4. A visual display can be observed by 

 several individuals simultaneously. This 

 provides a further restriction on the possi- 

 bilities of error. 



