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Physiological and behavioral concomitants of mild stress: The effects of accuracy of temporal information
JOURNAL
OF
RESEARCH
IN
PERSONALITY
Physiological
and
of Mild Accuracy
9, 168-i 76 ( 1975)
Behavioral
Stress:
Concomitants
The Effects
of Temporal
of
Information
MICHAEL G. H. COLES, SHARON D. HERZBERGER, BRENDA M. SPERBER, AND THERESE E. GOETZ University of Illinois
at
Urbana-Champaign
Sixty human subjects were exposed to a mild auditory stress after a fixed anticipatory period during which they performed a reaction time task. Suspense subjects were correctly informed of the time of onset of stress; Surprise subjects were told to expect the stress 10 min. later than it actually occurred. Subjects were provided with elapsed time information either automatically or on demand. Suspense subjects showed larger anticipatory electrodermal responses and smaller responses to stress than Surprise subjects but the two groups did not differ in their ratings of the unpleasantness of the stress. Female subjects showed greater anticipatory responses and consistently slower reaction times than males. The data are discussed in terms of explanations of the negative preception effect.
The relationship between information about the onset of aversive stimulation and physiological reactivity has been the focus of numerous investigations (Averill & Rosenn, 1972; Gaebelin, Taylor, & Borden, 1974; Lanzetta & Driscoll, 1966; Nomikos, Opton, Averill, & Lazarus, 1968). Knowledge about the impending aversive stimulus has been shown to affect physiological activity or performance during anticipation, impact, and recovery stages. Nomikos, Opton, Aver-ill, and Lazarus (1968) investigated the effects of time of onset of a stressful event on the physiological reaction to stress. Subjects were, or were not, given cues concerning the time of occurrence of an accident while they watched an industrial safety film. Subjects who received cues during the anticipation period showed larger increases in skin conductance during this period than subjects who received few or no cues. In a study relating the effects of anticipation to performance, Nash, Phelan, Demas, and Bittener (1966) found that simple reaction time was slower for subjects anticipating stress than for nonstressed subjects. In contrast, Wachtel (1968) found that stressed subjects had longer reaction times when asked to resnond to peripheral visual stimuli, but that Requests for reprints should be addressed to Michael G. H. Coles, Department of Psychology, University of Illinois, Champaign, IL 61820. 168 Copyright All rights
@ 1975 by Academic Press. Inc. of reproduction in any form reserved.
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AND
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169
they responded as quickly as nonstressed subjects when the stimuli were presented at the center of the visual field. Lanzetta and Driscoll (1966) found that subjects preferred warned to unwarned shock, and that the GSR reaction to the shock was signiiicantly less when the subject was warned. A similar effect was obtained by Gaebelin, Taylor, and Borden (1974) who found that the SC response was larger for subjects who received minimal temporal information about the occurrence of the shock than for subjects who received exact information. Measures of heart rate and skin conductance showed that warned subjects recovered more quickly than unwarned subjects. The present study explores the differential effects of a noxious stimulus under two conditions of information concerning the time of occurrence of the stress and two conditions of receiving temporal information. Each subject was told either the correct time interval between the beginning of the experiment and the onset of stress (Suspense) or he was told to expect a longer interval than actually occurred (Surprise). To examine the importance of temporal information during the anticipation period, some subjects (Active) were allowed to ask how much time had elapsed since the beginning of the experiment. Others (Passive) were given the elapsed time at regular intervals. It was predicted that, prior to stress. Suspense subjects would show higher levels of electrodermal activity than the Surprise subjects, due to the anticipation of imminent stress. It was also predicted that Surprise subjects would show larger responses to the stress and be slower to recover than the Suspense subjects. The present study also investigates the effects of the experimental manipulations and sex on both electrodermal and performance measures during anticipation, impact, and recovery stages. METHOD
Subjects Thirty male and 30 female undergraduate students from the University of Illinois participated in the experiment to fulfill a course requirement.
Apparatus and Procedure Each subject reported individually for the experiment. He sat in an easy chair in a partially sound-proofed, air-conditioned, room. Beckman electrodes, a 9842 coupler, and a Beckman R411 dynograph (which was located in an adjacent room) were used to provide a continuous DC recording of the subject’s skin conductance (SC). The electrodes (1 sq. cm. in area) were placed on the volar surfaces of the index and middle fingers of the nondominant hand, and a constant voltage of 0.5 V was imposed. Each subject was assigned to one of four experimental conditions: Active-Suspense (N = 10). Active-Surprise (N = lo), Passive-Suspense (N = 20), and Passive-Surprise (N = 20). Within each condition, half the subjects were male and half female. Active subjects were provided with a key which, when pressed, enabled the subject to hear through
170
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headphones the time that had elapsed since the beginning of the experiment. Passive subjects were given the elapsed time every 2 mins. Subjects in the Suspense group were correctly informed that they would receive a stress stimulus between 9 and 11 mins. after the beginning of the experiment. Surprise subjects were misinformed about the time of the stress stimulus, being told to expect it between 19 and 21 mins after the beginning of the experiment. Both groups were given the stress after 10 mins. 30 sets. The stress stimulus was a 5-sec. burst of white noise (105 db approx.) delivered through the same headphones that provided the elapsed time information. Each subject was warned that he would receive the stress stimulus and was given a sample of the stress before the experiment began. He was given the opportunity to leave the experiment at this time, but no one did. After the sample stress and at the end of the experiment, all subjects rated the unpleasantness of the stress on a scale from l- 10. Throughout the experimental session, the subject was required to perform a vigilance task which involved the detection of deflections on an oscilloscope (Telequipment D51) positioned 3 ft. in front of him. The beam was fixed horizontally in the middle of the screen and deflected vertically by 1 cm. for 440 msec. The subject responded to the deflection by pressing a key as quickly as possible with the index finger of his dominant hand. Active subjects were also able to press an elapsed time key with the ring finger of their dominant hand. As an inducement to respond quickly, subjects were told that the subject with the fastest reaction time (RT) would be given $5.00. Reaction times were recorded in analog form on a Hewlett Packard 3960 FM tape recorder and were subsequently derived using an IBM 1800. Five deflections occurred in every 30-sec. segment of the experiment. The average interval between deflections was 6 sets. (range 4-8 sets.). Before the experiment began the subjects were given practice at responding to the deflections and at requesting time (for the Active group only). The experimental period lasted 12 mins.
Scoring Measures of SC and RT were obtained for four 30-sec. segments of the experiment. These were the first 30 sets., the interval just prior to stress (between 10 mins. and 10 l/2 mins.), and the two 30-sec. segments after the one in which the stress occurred (between 11 and 12 mins). For SC, the mean value of two SC readings (to the nearest 0.5 pmho) at 7.5 and 22.5 sets. in a 30-sec. segment was taken to represent SC during that segment. For RT, the median value of the RTs to the five deflections in a 30-sec. segment was taken to represent the RT for the segment. Measures were also taken of the SC response to the stress stimulus. This was defined in terms of the SC level immediately prior to stress and the maximum level attained in response to stress. The RT to the first deflection in the interval between 10 l/2 mins. and 11 mins. was taken as representing RT under stress, since the stress stimulus was present during this deflection.
RESULTS
A series of analyses of variance were used to assess the effects of the experimental manipulations and sex on electrodermal and RT measures at different times during the experiment. Separate analyses were performed comparing groups with respect to measures (a) during the prestress period, (b) before and during stress, and (c) before and after the stress. For analysis (a), measures taken during the first 30 sets. of the experiment were compared with those during the last 30 sets. before
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stress. For analysis (b), median RT during the last 30 sets. before stress was compared to that for the deflection during stress; SC just prior to the stress was compared to the maximum level attained in response to stress. For analysis (c), comparisons were made between measures taken during the final 30 sets. before stress, and for the two 30-sec. segments after the segment in which the stress occurred. These analyses included three between-subjects factors (Suspense-Surprise, Active-Passive, and Sex) and one within-subjects factor (Time). Time. Skin conductance increased during the prestress period, F(1, 52) = 22.05, p < .Ol, and RT increased, F(lS2) = 8.21, p < .Ol. Skin conductance increased in response to stress, F(1,52) = 141.90, p < .Ol, and decreased after stress relative to the prestress level, F(2, 104) = 3.76, p < .05. Reaction time showed no change to stress but ratings of the unpleasantness of the stress stimulus increased from before to after the experimental session from 5.2 to 6.1, F( 1. 52) = 15.70, p < .Ol. Suspense vs. Surprise. The relevant data for SC are shown in Fig. 1. Suspense subjects tended to show a greater increase in SC during the prestress period F(1,52) = 2.66, p < .I 1. They showed a smaller response to stress F(1,52) = 4.11, p < .05, and quicker recovery after stress relative to the prestress level, F(2,104) = 3.47, p < .05, than Surprise subjects. Similar analyses on RT data failed to indicate any differential changes for the two groups.
1
FIGURE
phases
, 00.00-00.30 Pr*-str*ss
I 1040-1150 P.,,d
I is.1
pt. St....
I 11.00’1,.50 Po.t-str...
.
, 11.50-1240 P.r,*d
1. Skin conductance (in micromhos) during anticipation, stress, of the experiment, for Suspense and Surprise groups separately.
and recovery
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Active vs. Passive. Active and Passive groups failed to show differential changes on any of the measures for any of the three analyses. Sex. The relevant data for SC are shown in Fig. 2. There were differential changes in the prestress period with females showing a greater increase in SC than males, F(1,52) = 3.81, p‘< .05. There were no differences between the sexes in response to stress, but, relative to the prestress level, females showed a quicker recovery than males, F(2, 104) = 3.07, p < .05. Females had consistently slower RTs during all phases of the experiment, F(1,52) = 8.20, 8.52, and 11.60, p < .Ol in all cases. For females, mean RT was 319 msecs., and for males, 276 msecs. Over-all ratings of the stress stimulus indicated that females found it more unpleasant than did the males (6.2 vs. 5. l), F(1,52) = 6.19, p < .Ol, but males showed a greater increase in rating from the pre- to the postexperimental measurement, F( 1,52) = 5.22, p < .05. Interactions. Apart from the interactions between time and individual between-subject factors discussed above, there was a three-way interaction between Suspense-Surprise, Active-Passive, and Time for RT before and during stress, F(1,52) = 4.46, p < .05, which is not readily interpretable. Correlations. To determine whether electrodermal changes shown during the prestress period were related to the response to stress, correlations were computed between change in SC during the prestress period
FIGURE 2. Skin conductance (in micromhos) during anticipation, phases of the experiment, for males and females separately.
stress, and recovery
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173
and the SC response to stress. From law of initial value considerations (Wilder, 1950), it would be expected that the response to stress would be negatively correlated with the level of SC just prior to stress. Furthermore, it would be expected that SC just prior to stress would be positively correlated with the increase in SC shown during the prestress period. Therefore, the correlations between change in prestress SC and the SC response to stress were computed with the effects of the level just prior to stress partialled out. The relevant correlations were: -.47 for Surprise subjects, -.20 for Suspense subjects, and -.37 and -.49 for males and females, respectively (N = 30 in all cases: p < .05 for coefficients greater than .36). Thus, subjects who show large increases in SC during the prestress period tended to show smaller responses to stress than their counterparts, independent of the level of SC just prior to stress. DISCUSSION
The SC measure was clearly sensitive to the stress manipulation. There were increases in SC during the prestress period and in response to stress, and decreases after stress. As predicted, Suspense subjects tended to show larger increases in the anticipation period, smaller responses to stress, and were quicker to recover than the Surprise group. Since recovery was assessed relative to the prestress level, the latter result may be attributable to the fact that the Suspense group showed higher prestress levels than the Surprise group. Although Suspense subjects showed smaller responses to stress, there was no difference between the groups in the ratings of the unpleasantness of the stress obtained after the experimental period. The correlational data suggest that subjects who showed physiological evidence of anticipation (large increases in SC during the prestress period) gave smaller responses to stress than subjects who did not. Since this relationship was independent of the level of SC just prior to stress, these data indicate that the anticipation of stress leads to a reduction of the electrodermal stress response. This conclusion does not hold as strongly for the Suspense as for the Surprise group, presumably because the Suspense group was correctly anticipating the occurrence of stress. This would make the Suspense group more homogeneous with respect to the magnitude of the SC response to stress than the Surprise group. Indeed, the variance for the Suspense group was half that for the Surprise group. The two procedures for obtaining temporal information (Active and Passive) did not differentially effect electrodermal responses during the experiment. It was proposed that the provision of elapsed time information would allow subjects to engage in appropriate coping strategies. If
174
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ET
AL.
the information had such instrumental value, it would be predicted that Active Suspense subjects would obtain the information more often than Active Surprise subjects. In fact, the difference between the groups in the number of requests for temporal information, although in the predicted direction, was not significant. This failure to find a difference may be due to the fact that subjects believe that they are capable of estimating time, or that the stress stimulus was not particularly unpleasant. This latter factor may also have been responsible for the failure to find consistent effects of the experimental manipulations on RT. The over-all deterioration in performance during the period prior to stress was consistent with traditional research on vigilance performance (e.g., Mackworth, 1969). However, in the present study the deterioration in performance was accompanied by an increase in SC instead of the decrease usually found (e.g., Davies & Krkovic, 1965). The finding of sex differences in RT is consistent with previous research (e.g., Seashore & Seashore, 1941; Bellis, 1933) and may be attributable to differential arousal reflected in the SC measure, or fundamental differences in sensory-motor integration. These data have some bearing on explanations for the negative preception effect (Lykken, Macindoe, & Tellegen, 1972). “Negative preception” refers to the finding that the magnitude of electrodermal and other psychophysiological responses to shock is attenuated if the shock is preceded by a warning stimulus. To explain the effect, Lykken et al. (1972) have proposed that the presence of the warning stimulus permits the subject to engage in preparatory activity which results in an attenuation of the subjective intensity of the aversive event and a reduction in the magnitude of psychophysiological responses to the event. In contrast, Furedy and Klajner (1974) have argued against the need to invoke a preparatory explanation for negative preception and propose instead that it can be explained in terms of effector fatigue. They cite evidence to show that response attenuation is not accompanied by decreases in the rated intensity or unpleasantness of stress. In one respect, the results of the present study are consistent with these data and the effector fatigue hypothesis. Although the correctly warned and incorrectly warned groups differed in the magnitude of the electrodermal response to stress, they did not differ in subjective evaluation of the stress. However, in two other respects, the present data support the hypothesis advanced by Lykken et al. (1972). First, the correlational data show that, particularly for subjects in the incorrectly warned group, larger increases in SC during the prestress period are associated with smaller responses to stress. These correlations were obtained with the effects of SC level partialled out to take account of the Law of Initial Value. In one sense this law may be construed as a “Law of Effector Fatigue,” in that it
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proposes that high levels of SC (i.e., high effector activity) are associated with small SC responses. Thus, the partial correlations referred to above may be taken as representing a relationship between preparatory activity and the stress response with the influence of effector fatigue removed. The second respect in which the present data support Lykken et al. ( 1972) concerns the results for males and females. Although females showed larger increases in SC than males in the prestress period, the sexes did not differ in SC response to stress. This result can only be explained if a correspondence is assumed between the SC response to stress and the rating of the unpleasantness of stress (cf. Lykken et uf., 1972). Thus, since females rated the stress as being more unpleasant than did males, their greater prestress electrodermal activity may have served to reduce their response to the level shown by males. Clearly, a resolution of the controversy concerning the negative preception effect is beyond the scope of this study, particularly since Lykken and Tellegen (1974) have recently argued that the effect may be related to the impact rather than the perceived intensity of the aversive event. However, the present data do indicate that accurate temporal information about the onset of a negative event can influence electrodermal responses before and during the event. REFERENCES Averill, J. R., & Rosenn, M. Vigilant and nonvigilant coping strategies and psychophysiological stress reactions during the anticipation of electric shock. Journal qf Personality and Social Psychology, 1972, 23, 12% 14 1, Bellis, C. J. Reaction times and chronological age. Proceedings qf the Society of Experimental Biology and Medicine, 1933, 30, 801-803. Davies, D. R., & Krkovic, A. Skin-conductance, alpha-activity and vigilance. American Journal of Psychology, 1965, 78, 304-306. Furedy. J. J.. & Klajner, F. On evaluating autonomic and verbal indices of negative preception. Psychophysiology, 1974, 11, 12 I- 124. Gaebelin. J., Taylor, S. P., & Borden, R. Effects of an external cue on psychophysiological reactions to a noxious event. Psychophysiology, 1974, 11, 3 1 S-3.20. Lanzetta, J. T., & Driscoll, J. M. Preference for information about an uncertain but unavoidable outcome. Journal of Personality and Social Psychology, 1966.3, 96- 102. Lykken, D. T., Macindoe. 1.. & Tellegen, A. Preception: Autonomic response to shock as a function of predictability in time and locus. Psychophysiology, 1972. 9, 318-333. Lykken, D. T.. & Tellegen, A. On the validity of the preception hypothesis. Psv chophysiology.
1974, 11,
125-132.
Mackworth. J. F. Vigilance and habituation. Penguin Books. Harmondsworth, Middlesex. 1969. Nash, E. L.. Phelan, J. G., Demas, G., & Bittener, A. Effects of manifest and induced anxiety and experimenter variability on simple reaction time. Perceptual and Motor Skills, 1966. 22, 483-487. Nomikos, M. S., Opton, E., Jr., Averill, J. R., & Lazarus. R. S. Surprise versus suspense in the production of stress reaction. Journa/ of Personality and Social Psychology. 1968, 8, 204-208.
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Seashore, S. H., and Seashore, R. H. Individual differences in simple auditory reaction times of hands, feet and jaws. Journal of Experimental Psychology, 1941, 29, 342-345. Wachtel, P. L. Anxiety, attention and coping with threat. Journal of Abnormal Psychology, 1968.73, 137-143. Wilder, J. The Law of initial values. Psychosomatic Medicine, 1950, 12, 392-399.
OF
RESEARCH
IN
PERSONALITY
Physiological
and
of Mild Accuracy
9, 168-i 76 ( 1975)
Behavioral
Stress:
Concomitants
The Effects
of Temporal
of
Information
MICHAEL G. H. COLES, SHARON D. HERZBERGER, BRENDA M. SPERBER, AND THERESE E. GOETZ University of Illinois
at
Urbana-Champaign
Sixty human subjects were exposed to a mild auditory stress after a fixed anticipatory period during which they performed a reaction time task. Suspense subjects were correctly informed of the time of onset of stress; Surprise subjects were told to expect the stress 10 min. later than it actually occurred. Subjects were provided with elapsed time information either automatically or on demand. Suspense subjects showed larger anticipatory electrodermal responses and smaller responses to stress than Surprise subjects but the two groups did not differ in their ratings of the unpleasantness of the stress. Female subjects showed greater anticipatory responses and consistently slower reaction times than males. The data are discussed in terms of explanations of the negative preception effect.
The relationship between information about the onset of aversive stimulation and physiological reactivity has been the focus of numerous investigations (Averill & Rosenn, 1972; Gaebelin, Taylor, & Borden, 1974; Lanzetta & Driscoll, 1966; Nomikos, Opton, Averill, & Lazarus, 1968). Knowledge about the impending aversive stimulus has been shown to affect physiological activity or performance during anticipation, impact, and recovery stages. Nomikos, Opton, Aver-ill, and Lazarus (1968) investigated the effects of time of onset of a stressful event on the physiological reaction to stress. Subjects were, or were not, given cues concerning the time of occurrence of an accident while they watched an industrial safety film. Subjects who received cues during the anticipation period showed larger increases in skin conductance during this period than subjects who received few or no cues. In a study relating the effects of anticipation to performance, Nash, Phelan, Demas, and Bittener (1966) found that simple reaction time was slower for subjects anticipating stress than for nonstressed subjects. In contrast, Wachtel (1968) found that stressed subjects had longer reaction times when asked to resnond to peripheral visual stimuli, but that Requests for reprints should be addressed to Michael G. H. Coles, Department of Psychology, University of Illinois, Champaign, IL 61820. 168 Copyright All rights
@ 1975 by Academic Press. Inc. of reproduction in any form reserved.
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169
they responded as quickly as nonstressed subjects when the stimuli were presented at the center of the visual field. Lanzetta and Driscoll (1966) found that subjects preferred warned to unwarned shock, and that the GSR reaction to the shock was signiiicantly less when the subject was warned. A similar effect was obtained by Gaebelin, Taylor, and Borden (1974) who found that the SC response was larger for subjects who received minimal temporal information about the occurrence of the shock than for subjects who received exact information. Measures of heart rate and skin conductance showed that warned subjects recovered more quickly than unwarned subjects. The present study explores the differential effects of a noxious stimulus under two conditions of information concerning the time of occurrence of the stress and two conditions of receiving temporal information. Each subject was told either the correct time interval between the beginning of the experiment and the onset of stress (Suspense) or he was told to expect a longer interval than actually occurred (Surprise). To examine the importance of temporal information during the anticipation period, some subjects (Active) were allowed to ask how much time had elapsed since the beginning of the experiment. Others (Passive) were given the elapsed time at regular intervals. It was predicted that, prior to stress. Suspense subjects would show higher levels of electrodermal activity than the Surprise subjects, due to the anticipation of imminent stress. It was also predicted that Surprise subjects would show larger responses to the stress and be slower to recover than the Suspense subjects. The present study also investigates the effects of the experimental manipulations and sex on both electrodermal and performance measures during anticipation, impact, and recovery stages. METHOD
Subjects Thirty male and 30 female undergraduate students from the University of Illinois participated in the experiment to fulfill a course requirement.
Apparatus and Procedure Each subject reported individually for the experiment. He sat in an easy chair in a partially sound-proofed, air-conditioned, room. Beckman electrodes, a 9842 coupler, and a Beckman R411 dynograph (which was located in an adjacent room) were used to provide a continuous DC recording of the subject’s skin conductance (SC). The electrodes (1 sq. cm. in area) were placed on the volar surfaces of the index and middle fingers of the nondominant hand, and a constant voltage of 0.5 V was imposed. Each subject was assigned to one of four experimental conditions: Active-Suspense (N = 10). Active-Surprise (N = lo), Passive-Suspense (N = 20), and Passive-Surprise (N = 20). Within each condition, half the subjects were male and half female. Active subjects were provided with a key which, when pressed, enabled the subject to hear through
170
COLES ET AL.
headphones the time that had elapsed since the beginning of the experiment. Passive subjects were given the elapsed time every 2 mins. Subjects in the Suspense group were correctly informed that they would receive a stress stimulus between 9 and 11 mins. after the beginning of the experiment. Surprise subjects were misinformed about the time of the stress stimulus, being told to expect it between 19 and 21 mins after the beginning of the experiment. Both groups were given the stress after 10 mins. 30 sets. The stress stimulus was a 5-sec. burst of white noise (105 db approx.) delivered through the same headphones that provided the elapsed time information. Each subject was warned that he would receive the stress stimulus and was given a sample of the stress before the experiment began. He was given the opportunity to leave the experiment at this time, but no one did. After the sample stress and at the end of the experiment, all subjects rated the unpleasantness of the stress on a scale from l- 10. Throughout the experimental session, the subject was required to perform a vigilance task which involved the detection of deflections on an oscilloscope (Telequipment D51) positioned 3 ft. in front of him. The beam was fixed horizontally in the middle of the screen and deflected vertically by 1 cm. for 440 msec. The subject responded to the deflection by pressing a key as quickly as possible with the index finger of his dominant hand. Active subjects were also able to press an elapsed time key with the ring finger of their dominant hand. As an inducement to respond quickly, subjects were told that the subject with the fastest reaction time (RT) would be given $5.00. Reaction times were recorded in analog form on a Hewlett Packard 3960 FM tape recorder and were subsequently derived using an IBM 1800. Five deflections occurred in every 30-sec. segment of the experiment. The average interval between deflections was 6 sets. (range 4-8 sets.). Before the experiment began the subjects were given practice at responding to the deflections and at requesting time (for the Active group only). The experimental period lasted 12 mins.
Scoring Measures of SC and RT were obtained for four 30-sec. segments of the experiment. These were the first 30 sets., the interval just prior to stress (between 10 mins. and 10 l/2 mins.), and the two 30-sec. segments after the one in which the stress occurred (between 11 and 12 mins). For SC, the mean value of two SC readings (to the nearest 0.5 pmho) at 7.5 and 22.5 sets. in a 30-sec. segment was taken to represent SC during that segment. For RT, the median value of the RTs to the five deflections in a 30-sec. segment was taken to represent the RT for the segment. Measures were also taken of the SC response to the stress stimulus. This was defined in terms of the SC level immediately prior to stress and the maximum level attained in response to stress. The RT to the first deflection in the interval between 10 l/2 mins. and 11 mins. was taken as representing RT under stress, since the stress stimulus was present during this deflection.
RESULTS
A series of analyses of variance were used to assess the effects of the experimental manipulations and sex on electrodermal and RT measures at different times during the experiment. Separate analyses were performed comparing groups with respect to measures (a) during the prestress period, (b) before and during stress, and (c) before and after the stress. For analysis (a), measures taken during the first 30 sets. of the experiment were compared with those during the last 30 sets. before
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AND
171
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stress. For analysis (b), median RT during the last 30 sets. before stress was compared to that for the deflection during stress; SC just prior to the stress was compared to the maximum level attained in response to stress. For analysis (c), comparisons were made between measures taken during the final 30 sets. before stress, and for the two 30-sec. segments after the segment in which the stress occurred. These analyses included three between-subjects factors (Suspense-Surprise, Active-Passive, and Sex) and one within-subjects factor (Time). Time. Skin conductance increased during the prestress period, F(1, 52) = 22.05, p < .Ol, and RT increased, F(lS2) = 8.21, p < .Ol. Skin conductance increased in response to stress, F(1,52) = 141.90, p < .Ol, and decreased after stress relative to the prestress level, F(2, 104) = 3.76, p < .05. Reaction time showed no change to stress but ratings of the unpleasantness of the stress stimulus increased from before to after the experimental session from 5.2 to 6.1, F( 1. 52) = 15.70, p < .Ol. Suspense vs. Surprise. The relevant data for SC are shown in Fig. 1. Suspense subjects tended to show a greater increase in SC during the prestress period F(1,52) = 2.66, p < .I 1. They showed a smaller response to stress F(1,52) = 4.11, p < .05, and quicker recovery after stress relative to the prestress level, F(2,104) = 3.47, p < .05, than Surprise subjects. Similar analyses on RT data failed to indicate any differential changes for the two groups.
1
FIGURE
phases
, 00.00-00.30 Pr*-str*ss
I 1040-1150 P.,,d
I is.1
pt. St....
I 11.00’1,.50 Po.t-str...
.
, 11.50-1240 P.r,*d
1. Skin conductance (in micromhos) during anticipation, stress, of the experiment, for Suspense and Surprise groups separately.
and recovery
172
COLES ET AL.
Active vs. Passive. Active and Passive groups failed to show differential changes on any of the measures for any of the three analyses. Sex. The relevant data for SC are shown in Fig. 2. There were differential changes in the prestress period with females showing a greater increase in SC than males, F(1,52) = 3.81, p‘< .05. There were no differences between the sexes in response to stress, but, relative to the prestress level, females showed a quicker recovery than males, F(2, 104) = 3.07, p < .05. Females had consistently slower RTs during all phases of the experiment, F(1,52) = 8.20, 8.52, and 11.60, p < .Ol in all cases. For females, mean RT was 319 msecs., and for males, 276 msecs. Over-all ratings of the stress stimulus indicated that females found it more unpleasant than did the males (6.2 vs. 5. l), F(1,52) = 6.19, p < .Ol, but males showed a greater increase in rating from the pre- to the postexperimental measurement, F( 1,52) = 5.22, p < .05. Interactions. Apart from the interactions between time and individual between-subject factors discussed above, there was a three-way interaction between Suspense-Surprise, Active-Passive, and Time for RT before and during stress, F(1,52) = 4.46, p < .05, which is not readily interpretable. Correlations. To determine whether electrodermal changes shown during the prestress period were related to the response to stress, correlations were computed between change in SC during the prestress period
FIGURE 2. Skin conductance (in micromhos) during anticipation, phases of the experiment, for males and females separately.
stress, and recovery
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and the SC response to stress. From law of initial value considerations (Wilder, 1950), it would be expected that the response to stress would be negatively correlated with the level of SC just prior to stress. Furthermore, it would be expected that SC just prior to stress would be positively correlated with the increase in SC shown during the prestress period. Therefore, the correlations between change in prestress SC and the SC response to stress were computed with the effects of the level just prior to stress partialled out. The relevant correlations were: -.47 for Surprise subjects, -.20 for Suspense subjects, and -.37 and -.49 for males and females, respectively (N = 30 in all cases: p < .05 for coefficients greater than .36). Thus, subjects who show large increases in SC during the prestress period tended to show smaller responses to stress than their counterparts, independent of the level of SC just prior to stress. DISCUSSION
The SC measure was clearly sensitive to the stress manipulation. There were increases in SC during the prestress period and in response to stress, and decreases after stress. As predicted, Suspense subjects tended to show larger increases in the anticipation period, smaller responses to stress, and were quicker to recover than the Surprise group. Since recovery was assessed relative to the prestress level, the latter result may be attributable to the fact that the Suspense group showed higher prestress levels than the Surprise group. Although Suspense subjects showed smaller responses to stress, there was no difference between the groups in the ratings of the unpleasantness of the stress obtained after the experimental period. The correlational data suggest that subjects who showed physiological evidence of anticipation (large increases in SC during the prestress period) gave smaller responses to stress than subjects who did not. Since this relationship was independent of the level of SC just prior to stress, these data indicate that the anticipation of stress leads to a reduction of the electrodermal stress response. This conclusion does not hold as strongly for the Suspense as for the Surprise group, presumably because the Suspense group was correctly anticipating the occurrence of stress. This would make the Suspense group more homogeneous with respect to the magnitude of the SC response to stress than the Surprise group. Indeed, the variance for the Suspense group was half that for the Surprise group. The two procedures for obtaining temporal information (Active and Passive) did not differentially effect electrodermal responses during the experiment. It was proposed that the provision of elapsed time information would allow subjects to engage in appropriate coping strategies. If
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the information had such instrumental value, it would be predicted that Active Suspense subjects would obtain the information more often than Active Surprise subjects. In fact, the difference between the groups in the number of requests for temporal information, although in the predicted direction, was not significant. This failure to find a difference may be due to the fact that subjects believe that they are capable of estimating time, or that the stress stimulus was not particularly unpleasant. This latter factor may also have been responsible for the failure to find consistent effects of the experimental manipulations on RT. The over-all deterioration in performance during the period prior to stress was consistent with traditional research on vigilance performance (e.g., Mackworth, 1969). However, in the present study the deterioration in performance was accompanied by an increase in SC instead of the decrease usually found (e.g., Davies & Krkovic, 1965). The finding of sex differences in RT is consistent with previous research (e.g., Seashore & Seashore, 1941; Bellis, 1933) and may be attributable to differential arousal reflected in the SC measure, or fundamental differences in sensory-motor integration. These data have some bearing on explanations for the negative preception effect (Lykken, Macindoe, & Tellegen, 1972). “Negative preception” refers to the finding that the magnitude of electrodermal and other psychophysiological responses to shock is attenuated if the shock is preceded by a warning stimulus. To explain the effect, Lykken et al. (1972) have proposed that the presence of the warning stimulus permits the subject to engage in preparatory activity which results in an attenuation of the subjective intensity of the aversive event and a reduction in the magnitude of psychophysiological responses to the event. In contrast, Furedy and Klajner (1974) have argued against the need to invoke a preparatory explanation for negative preception and propose instead that it can be explained in terms of effector fatigue. They cite evidence to show that response attenuation is not accompanied by decreases in the rated intensity or unpleasantness of stress. In one respect, the results of the present study are consistent with these data and the effector fatigue hypothesis. Although the correctly warned and incorrectly warned groups differed in the magnitude of the electrodermal response to stress, they did not differ in subjective evaluation of the stress. However, in two other respects, the present data support the hypothesis advanced by Lykken et al. (1972). First, the correlational data show that, particularly for subjects in the incorrectly warned group, larger increases in SC during the prestress period are associated with smaller responses to stress. These correlations were obtained with the effects of SC level partialled out to take account of the Law of Initial Value. In one sense this law may be construed as a “Law of Effector Fatigue,” in that it
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proposes that high levels of SC (i.e., high effector activity) are associated with small SC responses. Thus, the partial correlations referred to above may be taken as representing a relationship between preparatory activity and the stress response with the influence of effector fatigue removed. The second respect in which the present data support Lykken et al. ( 1972) concerns the results for males and females. Although females showed larger increases in SC than males in the prestress period, the sexes did not differ in SC response to stress. This result can only be explained if a correspondence is assumed between the SC response to stress and the rating of the unpleasantness of stress (cf. Lykken et uf., 1972). Thus, since females rated the stress as being more unpleasant than did males, their greater prestress electrodermal activity may have served to reduce their response to the level shown by males. Clearly, a resolution of the controversy concerning the negative preception effect is beyond the scope of this study, particularly since Lykken and Tellegen (1974) have recently argued that the effect may be related to the impact rather than the perceived intensity of the aversive event. However, the present data do indicate that accurate temporal information about the onset of a negative event can influence electrodermal responses before and during the event. REFERENCES Averill, J. R., & Rosenn, M. Vigilant and nonvigilant coping strategies and psychophysiological stress reactions during the anticipation of electric shock. Journal qf Personality and Social Psychology, 1972, 23, 12% 14 1, Bellis, C. J. Reaction times and chronological age. Proceedings qf the Society of Experimental Biology and Medicine, 1933, 30, 801-803. Davies, D. R., & Krkovic, A. Skin-conductance, alpha-activity and vigilance. American Journal of Psychology, 1965, 78, 304-306. Furedy. J. J.. & Klajner, F. On evaluating autonomic and verbal indices of negative preception. Psychophysiology, 1974, 11, 12 I- 124. Gaebelin. J., Taylor, S. P., & Borden, R. Effects of an external cue on psychophysiological reactions to a noxious event. Psychophysiology, 1974, 11, 3 1 S-3.20. Lanzetta, J. T., & Driscoll, J. M. Preference for information about an uncertain but unavoidable outcome. Journal of Personality and Social Psychology, 1966.3, 96- 102. Lykken, D. T., Macindoe. 1.. & Tellegen, A. Preception: Autonomic response to shock as a function of predictability in time and locus. Psychophysiology, 1972. 9, 318-333. Lykken, D. T.. & Tellegen, A. On the validity of the preception hypothesis. Psv chophysiology.
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Mackworth. J. F. Vigilance and habituation. Penguin Books. Harmondsworth, Middlesex. 1969. Nash, E. L.. Phelan, J. G., Demas, G., & Bittener, A. Effects of manifest and induced anxiety and experimenter variability on simple reaction time. Perceptual and Motor Skills, 1966. 22, 483-487. Nomikos, M. S., Opton, E., Jr., Averill, J. R., & Lazarus. R. S. Surprise versus suspense in the production of stress reaction. Journa/ of Personality and Social Psychology. 1968, 8, 204-208.
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Seashore, S. H., and Seashore, R. H. Individual differences in simple auditory reaction times of hands, feet and jaws. Journal of Experimental Psychology, 1941, 29, 342-345. Wachtel, P. L. Anxiety, attention and coping with threat. Journal of Abnormal Psychology, 1968.73, 137-143. Wilder, J. The Law of initial values. Psychosomatic Medicine, 1950, 12, 392-399.