HUMAN FACTORS, 1975,17(1),106-109
Research Note: The Interactions Among Stress, Vigilance, and Task Complexity ROBERT S. KENNEDY'. and XENIA B. COULTER2. U. S. Naval Aerospace Medical Research Laboratory, Pensacola, Florida 3
A simple (olle-clza/mel) or a complex (tlzree-clzallllel) vigilance task was admillistered with or without tlzreat o[slwck to a large grollP o[flight studellts. It was [olllid tlzat a larger absolute decremellt lI'as obtailled ill tlze complex task, but tlze relative decremellts \Vere equivalellt [or botlz. Olle-clwlllieimollitorillg \Vas better overall tlzall three-clwlllielmollitorillg ;'1 tlze 11011stressed COllditioll. Stressed sllbjects performed betterthalllwlistressed, alld tlzis ellhallcemellt \Vas greater [or tlzree-clwlIIlelmollitorillg.
INTRODUCTION An auditory vigilance task. with a range of difficulties. reported by Kennedy (1971) is similar to the visual counting test of Jerison (1955. 1956). These tasks possess a number of attributes: (I) practice effects appear to be accomplished in 10 min. (Kennedy, 1971); (2) performance is inversely related to task complexity; (3) interaction effects among task complexity, performance. and subject variables are present (Kennedy. 1970b); (4) performance covaries with physiological indicants of arousal (Kennedy. 1970a); (5) work degredation is directly related to the magnitude of turbulence encountered during hurricane penetration (Kennedy. Moroney, Bale. Gregoire, and Smith. 1972); (6) a number of subjects may be tested simultaneously (Kennedy. 1970b); and (7) the test apparatus is I Now tocated at Human Factors Engineering Branch. Navat Missile Center, Point 1.Iugu, California. 2 Now located at Psychology Department. SUNY, Stony Brook. New York. l The opinions and statements contained herein are the private ones of the writers and are not to be construed as official or reflecting the views of the Navy Department or the Naval service at large.
simple. inexpensive. small. and can be made transportable. In a review of his experiments on noise and different performance tasks. Jerison (1959) suggested that noise may be a form of psychological stress. Further. the relationships between noise and performance may not be simple. at times improving and at times interfering with performance. A group of subjects was exposed to the threat of physical hurt (shock) while they performed either the simple (one-channel) or complex (three-channel) form of our vigilance task. It was hypothesized that threat stress would enhance performance on the simple task (arousal). but would interfere with performance on the complex task (distraction). Bergstroem (1970) offered a similar hypothesis for a tracking experiment and found that performance generally degraded under stress. although there was no relationship to task complexity. METHOD The vigilance task required the subject to attend to a high (1800 Hz). a middle (900 Hz).
106
February, 1975-107
ROBERT S. KENNEDY AND XENIA B. COULTER
and a low (100 Hz) tone heard at approximately 60 dB. The tones were presented 5, 6, and 8 times per min., respectively, and the low and middle tones were regular and presented every 7.5 and 10 sec., respectively. The high tone was presented every 10 sec. except that once per min. a double step (20 sec.) occurred. In the first experiment (Kennedy, 1971), cams driven by a l-r.p.m. motor were used to present the stimuli from which the magnetic tape recording for the present study was made. The stimulus presentation was repeated regularly every minute, but subjects reported that the presentations appeared random. All the subjects for the present experiment (N = 276) were student officers, naval aviation personnel. These men are typically homogeneous, physically elite, and intelligent. Testing was accomplished during their first week in the Navy. It was felt that this would obviate communication about the test between persons who had already taken it and those who had not. Additionally, past experience suggested that, at this time in their training, these men are highly motivated to perform. The pre-test for all subjects was the same. They were seated in a testing room in groups of8 -12. All were given response keys and instructed to listen for a high, a middle, and a low tone. Their task during this to-min. practice session was to count occurrences of low tones and, when a low tone had sounded four times, they were to ..... push a key and begin counting to four again; repeat until told to stop". They were told to ignore the high tone and middle tone. After the practice session, the subjects were assigned. randomly, to one of four groups. The experimental conditions for the four different groups were as follows. (1) One-channel task/without shock. These subjects (N = 124) were instructed to monitor the low tone as they did in practice (count to four repeatedly, etc.), but fora longer period of time, which was not specified.
(2)Three-channel task/without shock. These subjects (N = 82) were instructed to monitor the low tone as in practice and also to simultaneously, but independently, monitor the middle and high tones in the same way. (3) One-channel task/with shock. The instructions and task were identical to the one-channel/without shock condition, but these subjects (N = 35) were also told they would receive a painful shock some unspecified time within their watch. (4) Three-channel task/with shock. This task was the same as three-channel shock condition, but these subjects (N = 29) were told they would receive a painful shock as in the one-channel/with shock condition. The shock for the latter two groups was administered without warning at the end oftheir 35th min. during the vigilance task. The shock level was 80 V. of about 100 msec duration delivered at the volar surface of the arm by a standard Foringer shocking device. The authors arc reasonably sure, from a series of pilot studies on ourselves and colleagues, that this level was painful but relatively harmless. In a previous investigation (Kennedy, 1971), !t was demonstrated that percent correct was the best method of scoring vigilance performances because: (1) it had obvious face validity; (2) of several apparently valid methods of scoring, it had the highest intercorrelations; and (3) because it is a proportion, it allowed for a direct comparison of performances on one- and three-channel tasks. Percent correct was obtained by the calculation
-H
H +C +0
x 100;
where H = hits (defined as a response after the fourth signal and before the fifth), C= an early response (commission error), andO = a late response (omission error). The scoring is described in more detail in a previous study (Kennedy, 1971). Percent correct scores were obtained for each subject for each of the 12 5-min. segments in his 60-min. session.
IDS-February, 1975
FACTORS
HUMAN
A mixed-factor analysis of variance was chosen to test for group differences in performance between the one- and three-channel stressed and nonstressed conditions across the 12 5-min. periods ofwutchkeeping. Hence, the experimental design was a three-factor design with channels and stress representing between-subjects factors and trials representing the repeated measure factor (Winer, 1962, pp.337-340).
100 SHOCK
~
ONE CHANNEL
__________. :
80
SHOC"
------.. ....----_
ro
.............
Ott!:CHAlrisn 1II0S>«Xll:
.0 50
I
lHR[[ (HAMM[l
~:---,..,--
Research Note: The Interactions Among Stress, Vigilance, and Task Complexity ROBERT S. KENNEDY'. and XENIA B. COULTER2. U. S. Naval Aerospace Medical Research Laboratory, Pensacola, Florida 3
A simple (olle-clza/mel) or a complex (tlzree-clzallllel) vigilance task was admillistered with or without tlzreat o[slwck to a large grollP o[flight studellts. It was [olllid tlzat a larger absolute decremellt lI'as obtailled ill tlze complex task, but tlze relative decremellts \Vere equivalellt [or botlz. Olle-clwlllieimollitorillg \Vas better overall tlzall three-clwlllielmollitorillg ;'1 tlze 11011stressed COllditioll. Stressed sllbjects performed betterthalllwlistressed, alld tlzis ellhallcemellt \Vas greater [or tlzree-clwlIIlelmollitorillg.
INTRODUCTION An auditory vigilance task. with a range of difficulties. reported by Kennedy (1971) is similar to the visual counting test of Jerison (1955. 1956). These tasks possess a number of attributes: (I) practice effects appear to be accomplished in 10 min. (Kennedy, 1971); (2) performance is inversely related to task complexity; (3) interaction effects among task complexity, performance. and subject variables are present (Kennedy. 1970b); (4) performance covaries with physiological indicants of arousal (Kennedy. 1970a); (5) work degredation is directly related to the magnitude of turbulence encountered during hurricane penetration (Kennedy. Moroney, Bale. Gregoire, and Smith. 1972); (6) a number of subjects may be tested simultaneously (Kennedy. 1970b); and (7) the test apparatus is I Now tocated at Human Factors Engineering Branch. Navat Missile Center, Point 1.Iugu, California. 2 Now located at Psychology Department. SUNY, Stony Brook. New York. l The opinions and statements contained herein are the private ones of the writers and are not to be construed as official or reflecting the views of the Navy Department or the Naval service at large.
simple. inexpensive. small. and can be made transportable. In a review of his experiments on noise and different performance tasks. Jerison (1959) suggested that noise may be a form of psychological stress. Further. the relationships between noise and performance may not be simple. at times improving and at times interfering with performance. A group of subjects was exposed to the threat of physical hurt (shock) while they performed either the simple (one-channel) or complex (three-channel) form of our vigilance task. It was hypothesized that threat stress would enhance performance on the simple task (arousal). but would interfere with performance on the complex task (distraction). Bergstroem (1970) offered a similar hypothesis for a tracking experiment and found that performance generally degraded under stress. although there was no relationship to task complexity. METHOD The vigilance task required the subject to attend to a high (1800 Hz). a middle (900 Hz).
106
February, 1975-107
ROBERT S. KENNEDY AND XENIA B. COULTER
and a low (100 Hz) tone heard at approximately 60 dB. The tones were presented 5, 6, and 8 times per min., respectively, and the low and middle tones were regular and presented every 7.5 and 10 sec., respectively. The high tone was presented every 10 sec. except that once per min. a double step (20 sec.) occurred. In the first experiment (Kennedy, 1971), cams driven by a l-r.p.m. motor were used to present the stimuli from which the magnetic tape recording for the present study was made. The stimulus presentation was repeated regularly every minute, but subjects reported that the presentations appeared random. All the subjects for the present experiment (N = 276) were student officers, naval aviation personnel. These men are typically homogeneous, physically elite, and intelligent. Testing was accomplished during their first week in the Navy. It was felt that this would obviate communication about the test between persons who had already taken it and those who had not. Additionally, past experience suggested that, at this time in their training, these men are highly motivated to perform. The pre-test for all subjects was the same. They were seated in a testing room in groups of8 -12. All were given response keys and instructed to listen for a high, a middle, and a low tone. Their task during this to-min. practice session was to count occurrences of low tones and, when a low tone had sounded four times, they were to ..... push a key and begin counting to four again; repeat until told to stop". They were told to ignore the high tone and middle tone. After the practice session, the subjects were assigned. randomly, to one of four groups. The experimental conditions for the four different groups were as follows. (1) One-channel task/without shock. These subjects (N = 124) were instructed to monitor the low tone as they did in practice (count to four repeatedly, etc.), but fora longer period of time, which was not specified.
(2)Three-channel task/without shock. These subjects (N = 82) were instructed to monitor the low tone as in practice and also to simultaneously, but independently, monitor the middle and high tones in the same way. (3) One-channel task/with shock. The instructions and task were identical to the one-channel/without shock condition, but these subjects (N = 35) were also told they would receive a painful shock some unspecified time within their watch. (4) Three-channel task/with shock. This task was the same as three-channel shock condition, but these subjects (N = 29) were told they would receive a painful shock as in the one-channel/with shock condition. The shock for the latter two groups was administered without warning at the end oftheir 35th min. during the vigilance task. The shock level was 80 V. of about 100 msec duration delivered at the volar surface of the arm by a standard Foringer shocking device. The authors arc reasonably sure, from a series of pilot studies on ourselves and colleagues, that this level was painful but relatively harmless. In a previous investigation (Kennedy, 1971), !t was demonstrated that percent correct was the best method of scoring vigilance performances because: (1) it had obvious face validity; (2) of several apparently valid methods of scoring, it had the highest intercorrelations; and (3) because it is a proportion, it allowed for a direct comparison of performances on one- and three-channel tasks. Percent correct was obtained by the calculation
-H
H +C +0
x 100;
where H = hits (defined as a response after the fourth signal and before the fifth), C= an early response (commission error), andO = a late response (omission error). The scoring is described in more detail in a previous study (Kennedy, 1971). Percent correct scores were obtained for each subject for each of the 12 5-min. segments in his 60-min. session.
IDS-February, 1975
FACTORS
HUMAN
A mixed-factor analysis of variance was chosen to test for group differences in performance between the one- and three-channel stressed and nonstressed conditions across the 12 5-min. periods ofwutchkeeping. Hence, the experimental design was a three-factor design with channels and stress representing between-subjects factors and trials representing the repeated measure factor (Winer, 1962, pp.337-340).
100 SHOCK
~
ONE CHANNEL
__________. :
80
SHOC"
------.. ....----_
ro
.............
Ott!:CHAlrisn 1II0S>«Xll:
.0 50
I
lHR[[ (HAMM[l
~:---,..,--
