MEASUREMENTS OF STRESS 



431 



weight loss attributable to evaporative cool- 

 ing. The latter method, combined with 

 methods for maintaining balance of the re- 

 cording scales by continuous automatic com- 

 pensation (41), provides valuable indication 

 of short time changes in metabohc activity 

 under stimulation. 



10. The adrenal cortex and related changes 

 has been extensively studied following the 

 work of Long (77) and Selye (93) and others, 

 in relation to the "alarm reaction" or reac- 

 tions of stress. Central nervous system in- 

 fluences acting via the pituitary and secre- 

 tion of adrenocorticotrophic hormone may 

 increase secretion of adrenocortical homaone; 

 the amount of 17-ketosteroids excreted in 

 the urine provides an indication. Keto- 

 steroids in the blood may also cause destruc- 

 tion of lymphocytes, and cell counts may 

 provide an index of this effect. Studies of 

 effects of stress on adrenocortical activity 

 offer considerable promise (38, 39, 65, 77). 



11 . Electroencephalography offers means of 

 determining effects of stress within the brain 

 itself (26, 27, 76, 98). Effects of so-called 

 "tension" on the EEG have long been recog- 

 nized. Generally "tension" has been asso- 

 ciated with the presence of low voltage fast 

 activity, most pronounced in anterior areas. 

 Conversely, changes occurring with relaxa- 

 tion often associated with increase of the 

 alpha (10 per second) rhytlmi are familiar to 

 any electroencephalographer. Changes in 

 sleep with the disappearance of alpha and 

 the occurrence of spindles 12 to 14 per second 

 have also been extensively studied (59). 

 Combinations of EEG as an index of cerebral 

 activity with various of the above described 

 indicators of organic change offer a possibihty 

 for investigation of cerebral-organic inter- 

 relationsliips under stress (27, 60, 61). 



13. Other expressive indicators employed in 

 psychophysiological study are described by 

 various authors (11, 12, 16, 23, 28, 33, 35, 

 39, 51, 58, 60, 76, 79, 81, 83, 86, 90, 98, 101, 

 and 102). Methods of employing these in- 

 dicators for testing capacity for response and 



reaction to conditions of stress will be briefly 

 considered. 



B. Tests of Reaction to Stress 



Psychophysiological tests are desired which 

 will screen out incompetence under stress 

 with an effectiveness comparable with that 

 of test, interview, and trial duty methods 

 now in use. The problem of refining the al- 

 ready screened product of the selection mill 

 sets requirements extremely high. Prospec- 

 tive tests may be classified into four general 

 groups relating to the three types of stress 

 already outUned. Such tests may concern 

 (1) capacity for homeostatic adjustment to 

 conditions such as O2 lack, (2) capacity for 

 perfonnance under stress of duty, (3) emo- 

 tional stability and response under stimula- 

 tion, and (4) tests of chronic status involving 

 conditions of internally maintained activity 

 in the absence of specific stimulation. Tests 

 may combine these conditions of stress singly 

 or in varying proportions. For example we 

 may combine a test of performance and of 

 emotional stability under conditions of O2 de- 

 ficiency and observe the persisting effects on 

 chronic status. 



1 . Tests of capacity for homeostatic adjust- 

 ment are perhaps best illustrated by the 

 various studies of the effects of oxygen lack 

 under conditions of posture, CO2, tempera- 

 tures, blood sugar, etc., as cited in various 

 studies (5, 10, 11, 58, 86, 98, and 102). 

 Among the better test indicators may be 

 mentioned critical fusion frequency (cff), dy- 

 namic visual field (dvf), visual acuity, word 

 association, handwriting, code substitution, 

 steadiness, and color naming. Failure of re- 

 sponse to a signal may be used to indicate 

 loss of consciousness (102). These indicators 

 may involve an element of performance which 

 is an outstanding feature of tests of type 2. 

 An outstanding example of a test of homeo- 

 static adjustment is the Dreyer rebreathing 

 test (30), widely used in the selection of air 

 pilots in the first world war. 



S. Tests of performance under stress of 



