126 



RADAR SCOPES 



practical difference this would make in radar 

 work. Though not obtained on real radar 

 indicators, Hopkinson's data (24) are easily 

 the most relevant. He had his observer 

 use four different criteria of visibility : O, just 

 visible; C, just recognizable and easily visi- 

 ble; B, just visible with some discomfort, 

 enough judged to cause fatigue in extensive 

 work; and A, two traces just recognizable 

 as double. Although these sound like pecul- 

 iar psychological categories, they probably 

 made sense to the observer who used them. 

 At any rate, most of the visual functions in- 

 vestigated followed almost precisely the 

 same form no matter what the criterion; 

 that is, the curves were all nearly parallel. 

 Judging by his published graphs (no raw 

 data were given), it appears that the largest 

 difference, that is, between the just visible 

 (0) and the easily visible (C) is on the order 

 of a log unit-and-a-half of contrast. 

 Another kind of data relevant to this prob- 

 lem are those comparing the method of aver- 

 age error with the method of limits, that is, 

 the adjustment threshold compared with the 

 appearance threshold. At various times the 

 writer has made this comparison with the 

 result that the latter are greater than the 

 former by approximately two db, although 

 the size of the difference may increase with 

 low PRF or other special conditions. 



It is commonly known among radar oper- 

 ators that, depending on conditions, a per- 

 son may not report a pip seen only once. 

 In short, the operator tries to report targets, 

 not pips. When pips fluctuate and recur 

 only intermittently, what does it take to 

 make the operator sure that he can report 

 a target? Space limits discussion of this 

 interesting matter, but it is probably evi- 

 dent that it raises many psychological prob- 

 lems of great import. Unfortunately, no 

 scientific answers can be given at this time. 



Prolonged Search and Alertness 

 Attitude and Interests of the Operator 



The total number of targets identified by a 

 radar operator is probably more dependent 

 upon the operator's alertness and attention 



to his radar scope than to any other single 

 factor. The reason is quite obvious: if the 

 operator is not looking at his scope he can- 

 not see anything on it. Informal opera- 

 tional accounts and comments of military 

 officials agree that the operator often is not 

 looking at his scope even when he presum- 

 ably knows that he ought to be. If this is 

 the case, a study of the factors causing oper- 

 ator inattention ought to receive first prior- 

 ity in research. That it has not, is no doubt 

 due to the psychologists' inability to find 

 any practicable measures of such intangible 

 entities as attention and alertness. Various 

 schemes and devices have been suggested 

 for keeping an operator on the alert. Oc- 

 casional false "alerting" pips, "dummy" tar- 

 gets, more motivation by more pay or higher 

 military status, associated auditory signals, 

 automatic alerting bells triggered by physio- 

 logical concomitants of drowsiness, and 

 many other schemes have been mentioned. 

 None has proved itself as a practical solution. 

 Many a scheme might solve part of the prob- 

 lem, yet fail to turn a wide-awake operator's 

 eyes from a magazine back to the radar 

 scope. 



Length of Duty Period 



Another associated problem is the famihar 

 one known as "fatigue." It is now agreed 

 that almost nobody knows much about fa- 

 tigue or boredom except from his own sub- 

 jective experience. Consequently, measures 

 of performance decrement due to fatigue 

 tend to be unrehable and even contradictory. 

 There are no knoAVTi data which show any 

 effects of fatigue on visibility, although there 

 are two studies on efficiency of visual work. 

 The first is OSRD Report No. 3334 (35), 

 which showed a definite loss in time of effi- 

 ciency during prolonged A-scope operation. 

 The second study is by Mackworth (37) in 

 England. His subjects were set to watch 

 the movements of a pointer, a task thought 

 similar to radar operation in some respects. 

 Subjects missed seeing (or reporting) un- 

 announced movements more and more as 

 length of watch period increased. For an 



