Percephraland MotorSkills, 1991, 7 2 , 927-934.
O Perceptual and Motor Skills 1991
CARDIAC REACTIONS TO TWO PSYCHOLOGICAL STRESSORS, ACTING IN COMBINATION ' HOWARD S. HOFFMAN, TASLEEM KHAN, VALERIE PAPACONSTANTINOU AND FELICITY O'HERRON
Bryn Mawr College Summary.-56 student volunteers (mean age 21 yr.) participated in a study designed to assess how the Stroop procedure and delayed auditory feedback affect cardiac activity when they are used individually as well as when they are combined in the same task. In a preliminary study, listening to tape-recorded instructions on how to relax produced a significant decrease in cardiac activity. In the major study, when used individually, both the Stroop procedure and delayed auditory feedback produced significant increases in cardiac activity. The largest increase, however, occurred with systolic blood pressure and was induced by delayed auditory feedback. When the Stroop procedure was used in combination with delayed auditory feedback, systolic blood pressure again increased, but this effect was no greater than when delayed auditory feedback was used alone. This pattern of results implies that, when combined, the Stroop procedure and delayed auditory feedback have largely independent effects on cardiac activity and that, when tested under similar conditions, delayed auditory feedback has the larger effect.
The increase in cardiovascular activity induced by psychological stress has been the subject of numerous investigations (Henry & Cassell, 1969; Lipowski, 1975). Among the most widely used laboratory techniques for generating such stress in human subjects are the Stroop Color-Word Procedure (Breslow, Grand, & Freedman, 1980; Doehrman, Landau, & O'Connell, 1978; Stroop, 1935) and delayed auditory feedback (Yates, 1963). With the Stroop procedure, subjects are asked to call out the colors of the inks used to print a list of color names. Moreover, they are asked to do so as rapidly and as accurately as possible. The special feature of this task is that the names of the colors do not correspond to the colors of the inks in which the names are printed. The name "Green," for example, might be printed in yellow ink whereas the name "Yellow" might be printed in red ink. As a result, there is usually a certain amount of vocal~cconfusion and with it some measure of psychological stress. With delayed auditory feedback subjects ate also asked to call out a list of words but now they wear earphones and hear their own voice after it has been electronically delayed by about 500 msec. Like the Stroop procedure, delayed auditory feedback induces a certain amount of vocalic confusion and as with the Stroop proce'The Sherman Fairchild Foundation, 7 1 Archer Street, Greenwich, Connecticut 06830, made this work possible by providing summer research participation grants to Tasleem Khan, Felicity O'Herron, and Valerie Papaconstantinou. Request reprints from Dr. Howard S. Hoffman, Department of Psychology, Bryn Mawr College, Bryn Mawr, PA 19010-2899.
928
13. S. HOFFMAN, ETAL.
dure, to enhance stress, subjects are usually asked to read the material as rapidly and as accurately as possible. While both the Stroop procedure and delayed auditory feedback generate an increase in cardiac activity (Doehring, 1956; Hugdahl & Franzon, 1987), the relative magnitudes of these increases have not previously been assessed under circumstances that would permit direct comparisons. How the two procedures affect cardiac activity when they are combined in the same task has also not been evaluated. The research reported here was designed to examine these issues. I n particular, this work sought to document the increases in cardiac activity induced by the Stroop procedure and by delayed auditory feedback when they were used separately as well as when they were used in combination.
EXPERIMENT 1 To optimize the conditions under which increased cardiac activity might be assessed, we tried to arrange that the subjects be as relaxed as possible at the start of the stressful procedures. Exp. 1 was designed to assess whether listening to a set of tape-recorded instructions on progressive relaxation would be helpful in establishing a lowered baseline of cardiac activity against which the stressful effects of our experimental procedures would subsequently be measured. Method Subjects.-Twenty-eight experimentally naive student volunteers were recruited to participate in Exp. 1. O n the average their ages were approximately 20 years. There were 23 women and 5 men. Apparatus.-The experimental procedures occurred in an Industrial Acoustics Corporation sound-treated room, which contained a small desk and chair for the subject. Blood pressure and heart rate were measured with a Sharp Corporation automatic blood-pressure monitor (MB-800). Because this automated unit provided a printout of the subjects' systolic and diastolic pressures as well as heart rates, its use ensured that the measures of cardiac activity would be objective. All subjects wore earphones throughout the experimental procedure. They heard their instructions through the earphones, and some of them also heard an 8-rnin, tape-recorded message on progressive relaxation. * The tape-recorded message was played on a Sony TC-142 3-head cassette recorder that was located outside of the test chamber. The message was given by a male voice speaking in a calm, steady fashion. I t provided guidance on how to breathe in and out at a slow pace and asked the subject to focus on, and to relax, particular parts of the body, beginning with the head and neck and working slowly downward to the feet. 'This recording was produced by and is available from Thought Technology, Ltd., 2180 Belgrave Avenue, Montreal, PQ, Canada H4A 2L8.
929
CARDIAC REACTION TO STRESS
Procedure.-Subjects were tested individually. After being escorted into the chamber and seated comfortably at the desk, a subject was fitted with earphones and readings were obtained of systolic and diastolic blood pressure and also heart rate. The experimenter then removed the blood-pressure cuff, left the room, and shut the door. For half of the subjects (randomly selected), the tape-recorded relaxation message was then presented through the earphones. The rest of the subjects were told to relax and to sit as calmly as possible for the next 8 min. When the message was finished or 8 min. had elapsed, the experimenter reentered the chamber, refitted the blood-pressure cuff and obtained a second set of readings. The cuff and earphones were then removed, and the subject was debriefed and thanked. Results and Discussion In this experiment, measures of cardiac activity were obtained on each of two occasions. The first set of measures was obtained shortly after the subject entered the chamber. The second set was obtained after the subject had listened to the relaxation message or had been sitting quietly for the same amount of time.
BLOOD PRESSURE
95 BEFORE
AFTER
RELAXATION
BEFORE
AFTER
CONTROL
FIG 1. Mean decrement in systolic blood pressure before and after listening to the relaxation tape (at left) and before and after sitting quietly €or the same amount of time (at right)
Fig. 1 shows the average drop in systolic pressure for the subjects who listened to the relaxation message as well as for the subjects who served as controls. Tests for related measures were conducted to assess the statistical reliability of these declines. For these tests, the entries consisted of the difference between the initial measure of a given subject's systolic pressure and the measure obtained 8 min, later. Since the initial measure was always subtracted from the second measure, negative entries reflected a decline in systolic pressure. The tests for related measures indicated that both of the mean declines depicted in Fig. 1 were statistically significant (t,,s = 14.93 and 4.65, p < .05) for subjects who listened to the relaxation tape and the control subjects, respectively.
930
H. S. HOFFMAN, ETAL
A t test for independent measures was used to assess the statistical significance of the difference in the amounts of decline for subjects who listened to the relaxation tape versus subjects who were only asked to relax and sit quietly. The difference (t,, = 8.54, p < .05) is statistically significant, so exposure to the message on progressive relaxation reliably reduced cardiac activity. The pattern of results that emerged when the data for diastolic pressure and heart rate were analyzed was similar to that obtained for systolic pressure. Those results are not shown since, except for being somewhat less systematic than those for systolic pressure, they were otherwise consistent.
EXPERIMENT 2 Exp. 2 was designed to assess the way in which delayed auditory feedback and the Stroop procedure affect cardiac activity when these two procedures are used separately and in combination. The results of Exp. 1 showed that exposure to the relaxation message was more effective in calming a subject (as measured by a decline in cardiac activity) than merely asking the subject to sit quietly for a comparable amount of time. Exp. 2 capitalized on this finding by arranging that all subjects listen to the relaxation message prior to being exposed to a given stress procedure. Method Subjects.-Twenty-eight new student volunteers were recruited to participate in Exp. 2 . Their average age was approximately 2 1 years. There were 2 1 women and 7 men. Apparatus.-The apparatus was the same as in Exp. 1, but now a microphone inside of the chamber carried the subject's voice to the tape recorder located outside of the chamber. Now, when a given subject spoke into the microphone, his own voice was heard over the earphones and, depending on the setting on the tape recorder, it either occurred with no delay or i t was delayed by 500 msec. I n Exp. 2, subjects were required to read a list of words. They were printed on 8%-in. x 11-in. pieces of white cardboard which were laminated within clear plastic for protection. Both cards contained three columns of 37 red, green, yellow, blue, and black randomly selected color names. O n the card used for the Stroop procedure, the color names were printed in colors incongruous to the colors named whereas color names on the card used in the control procedure were written in the appropriate color of ink. For both the Stroop card and the control card, the sequence of names was identical on the two cards. Procedure.-After being escorted into the test chamber and fitted with earphones, all subjects listened to the tape-recorded message on progressive relaxation. Readings of blood pressure and heart rate were then obtained,
CARDIAC REACTION TO STRESS
93 1
and the subject was randomly assigned to receive one of four experimental conditions: Condition 1-Stroop procedure with delayed auditory feedback, Condition 2-Stroop procedure without delayed auditory feedback, Condition 3-Control procedure with delayed auditory feedback, or Condition 4-Control procedure without delayed auditory feedback. Depending on the condition assigned, the experimenter placed either the Stroop card or the Control card face down on the clipboard in front of the subjeft and then left the room. The subjects then heard a tape-recording of the following instructions through their earphones: In front of you is a list of words. When I say 'go,' turn the list over and state the color of ink in which each word is written. Go down the columns as quickly and as accurately as possible. Ignore the meaning of the words themselves and simply name the colors in which they are printed. After you have named the last color, say 'done.' At that time, your blood pressure and heart rate will once again be recorded.
About half-way through the experimental task, the subjects' progress was interrupted by the experimenter with a warning (through the earphones) to "go faster." This admonition was made regardless of the subjects' speed or accuracy in an attempt to induce greater stress. Once the task was completed, the experimenter reentered the test chamber and a final measurement of cardiac activity was taken. Following removal of the blood-pressure cuff and the earphones, subjects were debriefed and thanked. Results The changes in cardiac activity induced by the various conditions of stress were first submitted to two-way analyses of variance. For these analyses, each entry consisted of the difference between a given measure of a subject's cardiac activity following, as opposed to just before, the stress procedure. Since the prestress measure was always subtracted from the poststress measure, positive values were indicative of an increase in cardiac activity. There were three analyses of variance computed on these changes (one for systolic pressure, one for diastolic pressure, and one for heart rate). In these analyses only the main effect of delayed auditory feedback was statistically significant and this only for systolic pressure (F,,,,= 10.74, p < .05). This should not be interpreted to mean that these were the only reliable effects of stress in this study. In Exp. 2 there were 12 measures of the mean changes in cardiac activity that occurred in the course of the study (3 kinds of measures x 4 different experimental procedures). It is noteworthy that all 12 means were positive, indicating increases in cardiac activity. The likelihood of this happening if the procedures produced no stress is less than p = .001. Furthermore, of these 12 changes, 4 were significantly greater than O on a two-tailed t test for related measures (t6>2.45, p
O Perceptual and Motor Skills 1991
CARDIAC REACTIONS TO TWO PSYCHOLOGICAL STRESSORS, ACTING IN COMBINATION ' HOWARD S. HOFFMAN, TASLEEM KHAN, VALERIE PAPACONSTANTINOU AND FELICITY O'HERRON
Bryn Mawr College Summary.-56 student volunteers (mean age 21 yr.) participated in a study designed to assess how the Stroop procedure and delayed auditory feedback affect cardiac activity when they are used individually as well as when they are combined in the same task. In a preliminary study, listening to tape-recorded instructions on how to relax produced a significant decrease in cardiac activity. In the major study, when used individually, both the Stroop procedure and delayed auditory feedback produced significant increases in cardiac activity. The largest increase, however, occurred with systolic blood pressure and was induced by delayed auditory feedback. When the Stroop procedure was used in combination with delayed auditory feedback, systolic blood pressure again increased, but this effect was no greater than when delayed auditory feedback was used alone. This pattern of results implies that, when combined, the Stroop procedure and delayed auditory feedback have largely independent effects on cardiac activity and that, when tested under similar conditions, delayed auditory feedback has the larger effect.
The increase in cardiovascular activity induced by psychological stress has been the subject of numerous investigations (Henry & Cassell, 1969; Lipowski, 1975). Among the most widely used laboratory techniques for generating such stress in human subjects are the Stroop Color-Word Procedure (Breslow, Grand, & Freedman, 1980; Doehrman, Landau, & O'Connell, 1978; Stroop, 1935) and delayed auditory feedback (Yates, 1963). With the Stroop procedure, subjects are asked to call out the colors of the inks used to print a list of color names. Moreover, they are asked to do so as rapidly and as accurately as possible. The special feature of this task is that the names of the colors do not correspond to the colors of the inks in which the names are printed. The name "Green," for example, might be printed in yellow ink whereas the name "Yellow" might be printed in red ink. As a result, there is usually a certain amount of vocal~cconfusion and with it some measure of psychological stress. With delayed auditory feedback subjects ate also asked to call out a list of words but now they wear earphones and hear their own voice after it has been electronically delayed by about 500 msec. Like the Stroop procedure, delayed auditory feedback induces a certain amount of vocalic confusion and as with the Stroop proce'The Sherman Fairchild Foundation, 7 1 Archer Street, Greenwich, Connecticut 06830, made this work possible by providing summer research participation grants to Tasleem Khan, Felicity O'Herron, and Valerie Papaconstantinou. Request reprints from Dr. Howard S. Hoffman, Department of Psychology, Bryn Mawr College, Bryn Mawr, PA 19010-2899.
928
13. S. HOFFMAN, ETAL.
dure, to enhance stress, subjects are usually asked to read the material as rapidly and as accurately as possible. While both the Stroop procedure and delayed auditory feedback generate an increase in cardiac activity (Doehring, 1956; Hugdahl & Franzon, 1987), the relative magnitudes of these increases have not previously been assessed under circumstances that would permit direct comparisons. How the two procedures affect cardiac activity when they are combined in the same task has also not been evaluated. The research reported here was designed to examine these issues. I n particular, this work sought to document the increases in cardiac activity induced by the Stroop procedure and by delayed auditory feedback when they were used separately as well as when they were used in combination.
EXPERIMENT 1 To optimize the conditions under which increased cardiac activity might be assessed, we tried to arrange that the subjects be as relaxed as possible at the start of the stressful procedures. Exp. 1 was designed to assess whether listening to a set of tape-recorded instructions on progressive relaxation would be helpful in establishing a lowered baseline of cardiac activity against which the stressful effects of our experimental procedures would subsequently be measured. Method Subjects.-Twenty-eight experimentally naive student volunteers were recruited to participate in Exp. 1. O n the average their ages were approximately 20 years. There were 23 women and 5 men. Apparatus.-The experimental procedures occurred in an Industrial Acoustics Corporation sound-treated room, which contained a small desk and chair for the subject. Blood pressure and heart rate were measured with a Sharp Corporation automatic blood-pressure monitor (MB-800). Because this automated unit provided a printout of the subjects' systolic and diastolic pressures as well as heart rates, its use ensured that the measures of cardiac activity would be objective. All subjects wore earphones throughout the experimental procedure. They heard their instructions through the earphones, and some of them also heard an 8-rnin, tape-recorded message on progressive relaxation. * The tape-recorded message was played on a Sony TC-142 3-head cassette recorder that was located outside of the test chamber. The message was given by a male voice speaking in a calm, steady fashion. I t provided guidance on how to breathe in and out at a slow pace and asked the subject to focus on, and to relax, particular parts of the body, beginning with the head and neck and working slowly downward to the feet. 'This recording was produced by and is available from Thought Technology, Ltd., 2180 Belgrave Avenue, Montreal, PQ, Canada H4A 2L8.
929
CARDIAC REACTION TO STRESS
Procedure.-Subjects were tested individually. After being escorted into the chamber and seated comfortably at the desk, a subject was fitted with earphones and readings were obtained of systolic and diastolic blood pressure and also heart rate. The experimenter then removed the blood-pressure cuff, left the room, and shut the door. For half of the subjects (randomly selected), the tape-recorded relaxation message was then presented through the earphones. The rest of the subjects were told to relax and to sit as calmly as possible for the next 8 min. When the message was finished or 8 min. had elapsed, the experimenter reentered the chamber, refitted the blood-pressure cuff and obtained a second set of readings. The cuff and earphones were then removed, and the subject was debriefed and thanked. Results and Discussion In this experiment, measures of cardiac activity were obtained on each of two occasions. The first set of measures was obtained shortly after the subject entered the chamber. The second set was obtained after the subject had listened to the relaxation message or had been sitting quietly for the same amount of time.
BLOOD PRESSURE
95 BEFORE
AFTER
RELAXATION
BEFORE
AFTER
CONTROL
FIG 1. Mean decrement in systolic blood pressure before and after listening to the relaxation tape (at left) and before and after sitting quietly €or the same amount of time (at right)
Fig. 1 shows the average drop in systolic pressure for the subjects who listened to the relaxation message as well as for the subjects who served as controls. Tests for related measures were conducted to assess the statistical reliability of these declines. For these tests, the entries consisted of the difference between the initial measure of a given subject's systolic pressure and the measure obtained 8 min, later. Since the initial measure was always subtracted from the second measure, negative entries reflected a decline in systolic pressure. The tests for related measures indicated that both of the mean declines depicted in Fig. 1 were statistically significant (t,,s = 14.93 and 4.65, p < .05) for subjects who listened to the relaxation tape and the control subjects, respectively.
930
H. S. HOFFMAN, ETAL
A t test for independent measures was used to assess the statistical significance of the difference in the amounts of decline for subjects who listened to the relaxation tape versus subjects who were only asked to relax and sit quietly. The difference (t,, = 8.54, p < .05) is statistically significant, so exposure to the message on progressive relaxation reliably reduced cardiac activity. The pattern of results that emerged when the data for diastolic pressure and heart rate were analyzed was similar to that obtained for systolic pressure. Those results are not shown since, except for being somewhat less systematic than those for systolic pressure, they were otherwise consistent.
EXPERIMENT 2 Exp. 2 was designed to assess the way in which delayed auditory feedback and the Stroop procedure affect cardiac activity when these two procedures are used separately and in combination. The results of Exp. 1 showed that exposure to the relaxation message was more effective in calming a subject (as measured by a decline in cardiac activity) than merely asking the subject to sit quietly for a comparable amount of time. Exp. 2 capitalized on this finding by arranging that all subjects listen to the relaxation message prior to being exposed to a given stress procedure. Method Subjects.-Twenty-eight new student volunteers were recruited to participate in Exp. 2 . Their average age was approximately 2 1 years. There were 2 1 women and 7 men. Apparatus.-The apparatus was the same as in Exp. 1, but now a microphone inside of the chamber carried the subject's voice to the tape recorder located outside of the chamber. Now, when a given subject spoke into the microphone, his own voice was heard over the earphones and, depending on the setting on the tape recorder, it either occurred with no delay or i t was delayed by 500 msec. I n Exp. 2, subjects were required to read a list of words. They were printed on 8%-in. x 11-in. pieces of white cardboard which were laminated within clear plastic for protection. Both cards contained three columns of 37 red, green, yellow, blue, and black randomly selected color names. O n the card used for the Stroop procedure, the color names were printed in colors incongruous to the colors named whereas color names on the card used in the control procedure were written in the appropriate color of ink. For both the Stroop card and the control card, the sequence of names was identical on the two cards. Procedure.-After being escorted into the test chamber and fitted with earphones, all subjects listened to the tape-recorded message on progressive relaxation. Readings of blood pressure and heart rate were then obtained,
CARDIAC REACTION TO STRESS
93 1
and the subject was randomly assigned to receive one of four experimental conditions: Condition 1-Stroop procedure with delayed auditory feedback, Condition 2-Stroop procedure without delayed auditory feedback, Condition 3-Control procedure with delayed auditory feedback, or Condition 4-Control procedure without delayed auditory feedback. Depending on the condition assigned, the experimenter placed either the Stroop card or the Control card face down on the clipboard in front of the subjeft and then left the room. The subjects then heard a tape-recording of the following instructions through their earphones: In front of you is a list of words. When I say 'go,' turn the list over and state the color of ink in which each word is written. Go down the columns as quickly and as accurately as possible. Ignore the meaning of the words themselves and simply name the colors in which they are printed. After you have named the last color, say 'done.' At that time, your blood pressure and heart rate will once again be recorded.
About half-way through the experimental task, the subjects' progress was interrupted by the experimenter with a warning (through the earphones) to "go faster." This admonition was made regardless of the subjects' speed or accuracy in an attempt to induce greater stress. Once the task was completed, the experimenter reentered the test chamber and a final measurement of cardiac activity was taken. Following removal of the blood-pressure cuff and the earphones, subjects were debriefed and thanked. Results The changes in cardiac activity induced by the various conditions of stress were first submitted to two-way analyses of variance. For these analyses, each entry consisted of the difference between a given measure of a subject's cardiac activity following, as opposed to just before, the stress procedure. Since the prestress measure was always subtracted from the poststress measure, positive values were indicative of an increase in cardiac activity. There were three analyses of variance computed on these changes (one for systolic pressure, one for diastolic pressure, and one for heart rate). In these analyses only the main effect of delayed auditory feedback was statistically significant and this only for systolic pressure (F,,,,= 10.74, p < .05). This should not be interpreted to mean that these were the only reliable effects of stress in this study. In Exp. 2 there were 12 measures of the mean changes in cardiac activity that occurred in the course of the study (3 kinds of measures x 4 different experimental procedures). It is noteworthy that all 12 means were positive, indicating increases in cardiac activity. The likelihood of this happening if the procedures produced no stress is less than p = .001. Furthermore, of these 12 changes, 4 were significantly greater than O on a two-tailed t test for related measures (t6>2.45, p
