department of applied social studieslbms03.cityu.edu.hk/oaps/ss2007-4708-lcm278.pdfsystem will cause...
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Social stress and memory 1
Department of Applied Social Studies
Bachelor of Social Sciences in Psychology
SS 4708 Research Project in Psychology
FINAL YEAR PROJECT
BSSPSY-2007
The effect of social stress on delay recall
and working memory
Student name: Lo Chor Ming
Supervisor: Dr. Lai, Chuk Ling Julian
Social stress and memory 2
Abstract
Objective. This study tried to examine the effect of a modified version of Trier social
stress test (TSST) on delay recall of Chinese words with different valance, and
working memory
Methods. There were a total of 22 male participants in this experiment. The
experiment measured the delayed recall capacity for Chinese words of two different
delay schedules (1 day and 30 minutes delay). Working memory was also measured
by a reading span test. A modified version of Trier social stress test was used as a
stressor to induce stress to the participant before the recall tasks and the working
memory task. Physiological data and subjective mood was measured three times:
before the stress, during the stress, and immediate before the recall tasks. Valance
effect, stress induced impairment on declarative memory performance, and working
memory performance were tested in this experiment.
Results. The stress indices were not influenced by the stress treatment, and none of
the delayed recall category was significantly influenced by the stressor and the
working memory was also not influenced by the stressor.
Social stress and memory 3
Discussion. One of the possible explanations of the insignificant result is that the
level of stress induced in the participant was not high enough to activate hormonal
changes which are responsible for the memory impairment.
Social stress and memory 4
Table of content
Page
Abstract 2
Table of content 4
List of tables 5
Introduction and literature review 6
Method 14
Results 20
Discussion 23
Social stress and memory 5
List of tables
Page
Table 1: Means and Standard Errors for PANAS Scores 33
Table 2: Tests of Normality in stress estimator 34
Table 3: Means and Standard Errors for stress estimators 35
(Physiological measurement)
Table 4: Means and Standard Errors for adjusted delay recall score 36
Table 5: Tests of Normality in adjusted score of delay recall task 37
Table 6: Means and Standard Errors for reading span test 38
Table 7: Tests of Normality in reading span score 39
Social stress and memory 6
The effect of social stress on delay recall and working memory
Stress is inevitable in every daily life, people have different perception toward
stress, some might treat it as a disturbance and it could impair their daily functioning,
and some might treat it as a source of energy to push them in their work. Despite the
differences in perception of stress people may have, the biological responses in
humans toward acute stress are more universal. According to Nolen-Hoeksma (2007),
the physiological responses to stress involved two systems, including the autonomic
nervous system (ANS) and hypothalamus-pituitary-adrenocortical axis (HPA). For
ANS, when people face stress, the hypothalamus will activate the sympathetic branch
of ANS, namely sympathetic nervous system. The activation of sympathetic nervous
system will cause a number of body changes, those changes is called fight-or flight
response, which provide extra energy by increasing heart rate, breath rate, relaxing
bronchi, increase blood pressure, and release extra glucose in liver, etc. Epinephrine
and norepinephrine also release in response to the sympathetic activation. For HPA,
the hypothalamus release corticotrophin-releasing factor (CRF) to the pituitary gland.
In respond to the CRF, pituitary gland release adrenocorticotrophic hormone (ACTH)
to adrenal gland. As a result, the adrenal cortex in the adrenal gland will release
cortisol. The increase of cortisol will block the corticosteroid receptors in
hippocampus which is important for declarative memory in human beings (Kim, Koo,
Social stress and memory 7
Lee, & Han, 2005). Besides declarative memory, working memory could also be
influenced by stress. Several studies had provided supporting evidence of the effect of
stress impairing working memory function (Elzinga & Roelofs, 2005; Beilock & Carr,
2005; Al'absi, Hugdahl & Lovallo, 2002).
Researches had different findings on the effect of stress on memory, to integrate
these findings, Rozendaal (2002) suggested that glucocorticoids have both impairing
and enhancing effect on memory functioning, in specific, cortisol would enhance
memory consolidation and impair memory retrieval. A recent meta-analysis on the
topic of manipulating cortisol by drugs in human subjects and its effect to memory
partially supported Rozendaal’s theory, it shown that the cortisol can have impairment
effect on memory retrieval, but for the memory consolidation, it did not provide a
conclusive answer (Het, Ramlow & Wolf, 2005).
There are many moderators that can have influence on the effect of stress on
memory. Including the valance of the recall material (Kuhlmann, Kirschbaum, & Wolf,
2005; Kuhlmann, Piel, & Wolf, 2005; Jelicic, Geraerts, Merckelbach, & Guerrieri,
2004; Domes, Heinrichs, Rimmele, Reichwald, & Hautzinger, 2004), the circadian
cortisol rhythm (Het, Ramlow, & Wolf, 2005; Kuhlmann, Kirschbaum, & Wolf, 2005),
and the estrogen level (Kuhlmann & Wolf, 2005).
The valance effect is related to the beta-adrenergic activation in amygdala.
Social stress and memory 8
Without stress, the positive/negative valance words will trigger beta-adrenergic
activation in amygdala (Cahill, Prins, Weber & McGaugh, 1994), and this activation
was proven related to the enhancing memory effect of emotional content. In the study
of Cahill, Prins, Weber & McGaugh (1994), they had used the drug propranolol
hydrochloride which is the beta adrenergic receptors antagonist to manipulate the
beta-adrenergic activation level in amygdala, long term memory on emotional content
were tested in their study, result shown that beta-adrenergic activation was responsible
for enhancing the long term memory of emotional content. Added by McGaugh, &
Roozendaal (2002 as cited in Jelicic, Geraerts, Merckelbach & Guerrieri, 2004), the
epinephrine elevation due to stress will increase the activity in amygdala which is a
part that responsible for emotional memory. Therefore, without cortisol, stress and
emotional content will both have enhancing effect to declarative memory. But the
linkage between stress and cortisol could not be break that easily, cortisol will usually
be elevated during stress, the enhancing effect might then be inversed. An animal
study done by Kim, Koo, Lee, & Han (2005) showed that the beta-adrenergic
activation in amygdala was essential in the impairing memory effect done by stress.
In the study of Kuhlmann, Kirschbaum, & Wolf (2005), they had investigated the
effect of social stress (using Trier social stress test) to delayed recall and working
memory in 19 male participants. In their experiment, the participants had a learning
Social stress and memory 9
session during the first day, in the following day, the participants were treated by the
stressor, Trier social stress test (TSST).After a ten minutes delay after the stressor, the
participants were tested for delayed recall, using the materials which presented to
them at day 1. Working memory and attention were also tested using digit span and d2
test of attention. Result had shown that only emotional arousing words (both positive
and negative), recall significantly lower than the control group. This implied emotion
arousing material is essential for cortisol impairment effect on declarative memory.
For the working memory, their study did not obtain any significant result. An
opposing result had demonstrated in the study of Jelicic, Geraerts, Merckelbach &
Guerrieri (2004), there are 31 female and 9 male in their study, same as Kuhlmann,
Kirschbaum, & Wolf study, the stressor in this study was also TSST, the valance of
the recall material also included three types (positive, neutral, and negative). In their
study, they presented the recall materials in a modified version of auditory verbal
learning test, which those words was present to the participant verbally with a 2s
interval between each word. After the learning phase, the participants received the
TSST. Then the participants needed to recall those words in a recall session. The
result had shown that, emotional words (positive and negative) were better memorized
by the participants than the neutral words.
By comparing these two studies, the contradictory findings may due to two
Social stress and memory 10
possible reasons; firstly, the way of presenting the material could have different effect
on memory. Since Kuhlmann, Kirschbaum, & Wolf‘s study let the participant to learn
the words visually, but in Jelicic, Geraerts, Merckelbach & Guerrieri’s study, they
presented the material in a verbal way. The second reason may due to the recall
schedule, for Kuhlmann, Kirschbaum, & Wolf‘s study, they were testing the delayed
recall (1 day), but for Jelicic, Geraerts, Merckelbach & Guerrieri’s study, they were
testing the immediate recall (with 20 min TSST delay). The second explanation seems
to make more sense than the first one, in addition, a study done by Elzinga, Bakker &
Bremner (2005) partially supported this explanation. In their study, they had tested
both delayed recall (1 day) as well as immediate recall; the result of their study shown
that level of cortisol increase negatively correlated with the memory performance
only in delayed recall with emotional content. Elzinga, Bakker & Bremner’s study
seems to offer empirical evidence in answering the question of which recall schedule
will mostly affect by the impairment effect of cortisol, but as the author also
mentioned that their study was using only 16 female participants, without controlling
the estrogen level of each participant, it will possibly influence the cortisol
impairment effect.
The effect of estrogen toward cortisol impairment effect on memory had shown
in several animal studies (Sandstrom, 2005; Beiko, Lander, Hampson, Boon & Cain,
Social stress and memory 11
2004; Shansky, et. al. 2004). But in one human study done by Kuhlmann & Wolf
(2005), suggested that estrogen level may not significantly affect the cortisol
impairment effect. But oral contraceptives may decrease the cortisol impairment
effect in women. In their study, they had tested the delay recall (1 hour) of three
groups, including women in luteal phase, during mensis, and women who taking oral
contraceptives (OC) during that period. The result shown that only OC group did not
have cortisol impairment effect in the recall session. This study provided evidence
that taking oral contraceptives may diminish the effect of cortisol impairment on
memory. Therefore, without taken this factor into consideration, Elzinga, Bakker &
Bremner’s study may not provide the real answer to the question of “which recall
schedule will mostly affected by the impairment effect of cortisol.” Therefore in the
current study, all of the participants were male to prevent any possible effect of
estrogen and oral contraceptives.
The relationship between working memory and stress is another focus of this
study, animal study had suggested that the glucocorticoid (similar to cortisol in human)
had impairment effect on working memory. (Abidin, et al., 2004). But the relationship
of stress and working memory might be more complex. In the study of Cerqueira, et
al (2005), they tried to manipulate Glucocorticoid receptors (GRs) and
mineralcorticoid receptors (MRs) by different treatment, including glucocorticoid
Social stress and memory 12
dexamethasone (used to activate GR only), corticosterone (activate both GRs and
MRs), adrenalectomization (a surgical procedure which make GRs and MRs
unoccupied). And the rodents were tested for spatial working memory in a hidden
platform water maze task, result shown that the only group that had impaired working
memory was the dexamethasone treatment group. Thus it provided a counter
argument to corticosteroid is the main factor that influences working memory
performance. Added by Abidin, et al. (2004), nitrite levels of frontal cortex and
thiobarbituric acid reactive substances in hippocampus and frontal cortex would also
correlated with the memory performance induced by stress. The concentration of
those substances was also the products of stress and learning. Therefore when we
consider the working memory performance, solely considering cortisol was not
adequate.
Although the focus in animal study of stress effect on working memory was so
diverse, the focus of similar study in human subject still focusing only on cortisol. For
example, the study of Al'absi, Hugdahl, & Lovallo (2002), they had measured the
dichotic listening and arithmetic performance after the treatment of a modified Trier
social stress test. The cortisol level were measured to distinguish between high
responders and low responders, result showing that the arithmetic performance were
impaired in the high responders group, but for the dichotic listening task, the
Social stress and memory 13
performance were inverse in two group. The author explained that the result was due
to different allocation of cognitive resources in two groups, in which high stress
responders tend to had more resources allocated in the sensory input, in contrast, low
stress responders tends to had less resources allocated in the sensory input, thus they
could use more resources in arithmetic task and get better performance. But the result
could also interpret in other way, since the stressor in that experiment was TSST, the
TSST already consisted of an arithmetic task as an stressor, if a person was especially
good at mental arithmetic calculation, he or she might found that the arithmetic task
really easy and they do not felt any stress during TSST, thus if this argument was true,
the low responder is equal to the people who is better in mental arithmetic calculation.
It explained the result of why low responders have a better result in the arithmetic
tasks.
Due to the resources constraint, the present study only focused on declarative
memory with different delay schedule to test which stage of memory process it mostly
affected. Valance effect suggested by previous study was also taken into consideration.
Working memory was also another focus of this study; the measurement of working
memory would not be the digit span which used in many other studies, such as the
study of Kuhlmann, Piel, & Wolf, (2005). Since, as suggested by Daneman & Merikle
(1996), reading span tests have a higher reliability, and it also had higher criterion
Social stress and memory 14
validity compare with digit span test in measuring working memory.
Method
Participants
A total of 22 male undergraduate students (City university of Hong Kong)
volunteer to participate in this experiment. 13 of them were recruited from the lecture
visit and doing the experiment is part of their course requirement. 9 of them were
recruited from the same university on friendly bases and they do not have the same
experiment requirement as the first 13 participant having. All of them were self
reported healthy and do not under any medication.
Materials
For the delay recall tasks and the baseline memory performance measurement,
three parallel lists of words (L1, L2, and L3) were prepared. Each contains a total of
21 Chinese words in 3 valance categories (positive, negative, and neutral), in other
words there are 7 positive, 7 neutral, and 7 negative words in each list. Due to the
possible word frequency effect suggested by Chastain, Garvin, Ferraro & Richard, F.
(1996), the words were controlled for the number of stroke (15 to 25 strokes total in
two characters) and word frequency in a pilot study. The sequence of word in the list
will be balanced between participants to cancel out the serial position effect.
A modified Chinese version of reading span test was used in measuring working
Social stress and memory 15
memory capacity in the experiment. The test contained 5 sets of 5 sentences; the
sentences appeared on a computer screen controlled by the experimenter one by one,
and the participant were required to read aloud the sentences, and at the same time to
memorize the last word (with 2 characters) and report to the experimenter verbally
after each set. The experimenter immediately switched to the next sentence as soon as
the participant had finished reading each sentence. The participants were told not to
slow down or make unnecessary pauses when reading. It is because the study by
Friedman & Miyake (2004) found that without those precautions, the participants
might have a greater chance of applying their own memorizing strategy, such as
taking extra time to rehearse the words for a few times before moving to next
sentence. And those strategies would decrease the reliability of the reading span test.
The total number of correct recall was used as the reading span score, which was
suggested by Friedman & Miyake (2005) to have a higher reliability and criterion
validity.
A modified version of Trier social stress test (TSST) was used as the social
stressor in the experiment. The test contained two phases, in phase one, which was the
public speaking phase, the participant would have 5 minutes to prepare a topic about
his/her own personal background. After the preparation, they were required to do a 5
minutes presentation in front of a camera and the judge (the experimenter). In phase
Social stress and memory 16
two, the participant were required to finish a reading span test, which is the one
mentioned in the previous paragraph. Between phase one and phase two, there was a
subjective mood measurement and a physiological measurement, in order to evaluate
the effectiveness of the stressor.
Subjective mood was measured by the Positive and Negative Affect Schedule
(PANAS). It was used in three different times during the experiment, including the
baseline measure (at the beginning of the second day), during the stress, and
immediate before the mixed recall task.
To evaluate participants’ autonomic responses to the stressor, a blood pressure
and pulse monitor (Cristix digi memo CX-68, A&D medical 6A767 plus 30) was used
in the experiment to measure the blood pressure and heart rate three times through out
the experiment, including the baseline measure (at the beginning of the second day),
during the stress, and immediate before the mixed recall task.
Procedure
The experiment last for two consecutive days. Each experimental session only
began at 10:30 am or 11:30 am, in order to control the potentially confounding effect
of the circadian rhythm of cortisol.
In day one of the experiment, the baseline memory ability was measured in an
immediate recall test. A list of word (L1) was presented using the PowerPoint, each
Social stress and memory 17
word lasted for 5 seconds on the screen and the next word appeared automatically
after the previous word. Participants were required to memorize as many words as
they could in the list. After the learning session, the participants were asked to do for a
5 minutes free recall on the words that had appeared in the previous session. The total
score of recall will served as the baseline memory performance of each participant
and it would be use to evaluate the change in memory performance. After the baseline
measurement, a parallel word list (L2) similar to L1 was presented in the same
procedure as presenting L1. The participants were told to have a recall session in the
coming day on L2.
In the following day (Day 2), upon arrival, the participants were asked to fill in
the Positive and Negative Affect Schedule (PANAS). After that, the experimenter
measured their heart rates and blood pressures for the first time. After the mood and
physiological measurement, another word list (L3) presented in the same way as L2
and L1 to the participants. Also the participants were told to have a recall session in
the later part of this experiment (mixed recall session) on L3. Then, a modified
version of Trier Social Stress Test (TSST) was presented to the participants, which is a
procedure aimed to induce stress to the participants. For the control group, the public
speaking task was replaced by a writing task which did not have any judge or camera
in the room. Immediately after the first phase, the experimenter temporarily removes
Social stress and memory 18
the camera and measured their subjective mood by PANAS and physiological
responses (2nd mood and physiological measurement). After the measurement, the
participants went to the second phase of TSST, which was the first reading span task.
In phase 2 of TSST, the only difference between experimental group and control
group is that the camera was present in the experimental group, but there was no
camera in the control group. Therefore, the experimental group and control group at
this moment both had the first reading span score measured. Immediate after TSST,
they were allowed to had a 5 minutes break. Then, the experimenter measured their
mood and physiological parameters for the third time. After the measurement, the
participants were asked to have a mixed free recall on the words which had appeared
in L2 or L3 within 5 minutes. And after the recall session, the second reading span test
was given to the participants in order to measure their working memory performance
after stress. The participants were then fully debriefed.
Statistical analysis
Due to the small number of participant, all the data collected were subjected to
the test of normality (Shapiro-Wilk test). If the result shown that a particular data
group was significantly deviated from normality, nor-parametric tests would be used
to test the related hypothesis.
Since the memory ability of different person may vary, therefore, the score of
Social stress and memory 19
recall tasks in each valance was expressed as percentage in relation to the baseline
measure (Kuhlmann, Piel, & Wolf, 2005) The detailed computation are as follow :
Adjusted score = Number of correct recall in valance group X in list Y / (number of
correct recall in baseline measure / 3), where X can be positive, neutral, or negative, Y
can be 2 (indicate that the recall with 1 day delay) or 3 (indicate that the recall with 30
minutes delay).
For the stress indices (e.g., mood and autonomic responses), 2 ways ANOVAs
were used to test the effectiveness of the stressor. If there were at least one group of
the data significantly deviated from normality, two different tests would be used to do
the within group comparison (in experimental group) and between group comparison
(measure during the stress). At least one of the two test would be nonparametric
depends on which group of data was deviated from normality.
For testing the overall memory impairment effect by stress, 6 independent
sample t-tests was used to compare the adjusted recall score between control group
and experimental group in 2 recall schedules with 3 valance types. If the data was
significantly deviated from normality, nonparametric tests (Mann-Whitney Test)
would be used in that particular pair of comparison.
For testing the valance effect, 2 ways ANOVAs were used. If there were at least
one group of the data significantly deviated from normality, Friedman Test would be
Social stress and memory 20
used in the experimental group.
For testing the working memory, 2-way ANOVAs with repeated measures were
used.
Results
Stress Indices
The results of subjective mood measurement were shown in Table 1. From Table
2, test of normality shown that the control group of the positive affects measurement
during TSST (PA2) was significantly deviated from normal distribution,
(Shapiro-Wilk test of normality statistic=0.8347, p < .05). A one way ANOVA with
repeated measures on positive affect in experimental group showed that there were no
significant changes of positive affect score in experiment group, F (2, 20) = 0.744;
p>0.1. Mann-Whitney Test was used to compare the difference of PA between control
and experimental group during stress (measure 2), no significant result was observed
(U=35.5; p>0.05), with control group having the mean rank of 13.77 and
experimental group of 9.23.
Data of negative affect (NA) measure was analyzed with ANOVAs with the
factors treatment (control and experimental) and time (measure 1, measure 2, measure
3). Result showed that there was no significant treatment by time interaction effect
F (2, 40) =3.506; p>0.05). No main effect on measure time (F (2, 40) =2.902; p>0.05)
Social stress and memory 21
and group (F (1, 20) = 0.447; p>0.5) were observed.
The result of physiological measurement was shown in Table 3. From Table 2,
test of normality showed that 2 groups of data were significantly deviated from
normality. Including the experimental group of systolic measure 1 (Shapiro-Wilk test
of normality statistic=0.8338; p<0.05) and the control group of systolic measure 3
(Shapiro-Wilk test of normality statistic=0.8106; p<0.05) Therefore, nor-parametric
test would be used in testing the systolic measure. The result for Friedman Chi Square
was (2, N=11) = 5.070, p<.05, no significant different between three measures of
systolic pressure in experimental group, the mean ranks of three measurement were as
follow: measure 1 mean rank was 1.77, measure 2 mean rank was 2.55, and measure 3
mean rank was 1.68. Mann-Whitney Test was used to compare the difference between
control and experimental group in measure 2, result showed that the systolic pressure
in experimental group was significantly higher than control group (U=30.5; p<0.05),
with control group having the mean rank of 8.77 and experimental group of 14.23.
Data of diastolic pressure (DIA) was analyzed with two way ANOVAs with the
factors treatment (control and experimental) and time (measure 1, measure 2, measure
3). Result shown that there was no significant treatment by time interaction effect, F(2,
40) = 0.259; p>0.1. There was no main effect of measurement time (F (2, 40) = 1.564;
p>0.1). But the main effect of group was observed (F (1, 20) = 5.950; p<0.05).
Social stress and memory 22
Data of heart rate (HR) was analyzed with two way ANOVAs with the factors
treatment (control and experimental) and time (measure 1, measure 2, measure 3).
Result shown that there was no significant treatment by time interaction effect, F (2,
40) = 0.350; p > 0.1. The main effect of measurement time was observed. (F (2, 40) =
6.394; p<0.005) And there was no main effect of group (F (1, 20) = 0.001; p>0.1)
Recall Tasks
The result of recall tasks was shown in Table 4. From Table 5, test of normality
shown that 3 groups of data were significantly deviated from normal distribution,
which was the positive valance words in experimental group in 1 day delay recall
(Shapiro-Wilk test of normality statistic=0.6362; p<0.001), negative valance words in
experimental group in 1 day delay recall (Shapiro-Wilk test of normality
statistic=0.7647; p<0.005), and negative valance word in control group in 30 minutes
delay recall (Shapiro-Wilk test of normality statistic=0.8501; p<0.05)
Due to the normality of data, Mann-Whitney Test was used to test the between
group differences in positive valance with 1 day delay, negative valance with 1 day
delay, and negative valance in 30 minutes delay. And the rest of the between group
comparison will be tested using independence sample t test. Results showed that none
of the six between group comparisons had significant difference. The tests results
were as follow: For one day delay, positive valance (U=41.5; p>0.1). Neutral valance
Social stress and memory 23
(t (20) =1.437; p>0.05). Negative valance (U=44.5; p>0.1). For 30 minutes delay,
positive valance (t (20) = 0.429; p>0.1). Neutral valance (t (20) = -0.142; p>0.1).
Negative valance (U=37.5; p>0.1).
In testing the valance effect in the experimental group, Friedman test was used in
testing the within group valance comparison for one day delay recall, Friedman Chi
Square was (2, N=11) = 2.074, p>.01, no significant valance effect was observed. One
way ANOVA with repeated measure was used to test the same comparison in 30
minutes delay recall, result shown that there was no significant difference between
three valances F (2, 20) =2.221; p>0.1.
Working Memory
The result of recall tasks was shown in Table 6. From Table 7 we could see that
none of the group in the reading span test was significantly deviated from normal
distribution, therefore, 2 way ANOVAs with repeated measures would be used. Test
result shown no treatment by time interaction effect (F (1, 20) = 0.403; p > .1). The
main effect of time was observed, F (1, 20) = 38.264; p<.001, but the main effect of
group was not observed, F (1, 20) = 0.197; p > .10.
Discussion
The present study did not yield any significant findings for all of the main
hypotheses; there was no observable stress-induced impairment on recall in both
Social stress and memory 24
recall schedules (1 day delay and 30 minutes delay) across the three different valances
(positive, neutral, negative). The valance effect was also shown to be nonsignificant,
where positive, neutral, and negative words did not have significant differences in
recall rate as the hypothesis had predicted. Working memory test showed only the
practice effect, which was the main effect of time which tested significant in the F test,
but the test showed not significant for the working memory impairment due to the
stress treatment.
The nonsignificant result might be explained by the changes in the stress indices.
For systolic pressure, although the between group comparison of systolic pressure in
experimental group was significantly higher than control group, but the within group
comparison in experimental group was showed to be insignificant, therefore, it was
not appropriate to said that the systolic pressure difference was due to the stressor
itself. For diastolic pressure, although the main effect of group was observed, where
the diastolic pressure in experimental group was higher that in the control group, but
the group by measure interaction effect was tested insignificant, therefore the main
effect of group difference might due to the individual differences and small number of
participants. For heart rate, although the main effect of measurement time was
observed, but there was no treatment by group interaction effect, we did not have
enough evidence to say that the main effect was only due to the stressor itself. For
Social stress and memory 25
both PANAS scores (PA and NA), there were no significant result obtained, therefore
the subjective mood was not influenced by the stressor. In sum, the subjective mood
measurement (PANAS) and physiological data showed that the stressor itself was too
weak to neither trigger the physiological response nor alter the participants’ subjective
mood.
As mentioned by Nolen-Hoeksma (2007), acute stress will trigger a set of
physiological response and two of them are the blood pressure and heart rate. The
insignificant result in comparing the systolic pressure, diastolic pressure, and heart
rate indicated that those set of physiological response might not be present in the
participants, which showed that ANS and HPA was not stimulated by the experiment
stressor. Thus, the participants’ cortisol level--- the crucial factor which involve in
impairing memory functioning, might not have any elevation due to the experiment
stressor. Mentioned by Elzinga & Roelofs (2005), sympathetic activation was
essential for the cortisol induced working memory impairment, both cortisol elevation
and sympathetic activation was not present in this experiment, therefore the working
memory impairment effect was almost impossible to exist.
The reason why the stressor was not as stressful as expected may due to several
reasons. Firstly, compare with the other Trier social stress test (TSST) used in other
similar experiment, such as the experiment of Kuhlmann, Piel, & Wolf (2005), the
Social stress and memory 26
standard TSST involve a switching room procedure, which after the participants had
finished the preparation stage of the public speech, the were asked to go to the next
room to perform the public speech. The current study did not have this switching
room procedure. Moving to a new room to perform the public speech is more stressful
than no need to move to a new room. Since people usually feel more stress in moving
to a new environment. Secondly, the judge used in the present study was the
experimenter himself, similar to the room switching procedure, meeting a new judge
or a group of new judges should have better effect for inducing stress. Thirdly, as
mentioned in the participant part of this report, 9 out of 22 participants was recruited
on friendly bases. Despite the fact that none of them were psychology student, some
of the participants knew the experimenter long before the experiment was started. The
familiarity to the experimenter might significantly reduce the stress level in those
participants during the experiment, therefore it compensated the effect done by the
stressor and the expected stressful situation cannot be fully obtained in the TSST.
In this experiment, we did not have any measurement on the cortisol level in the
participant. In many other similar studies, such as the study of Putman, van Honk,
Kessels, Mulder & Koppeschaar (2004), the salivary free cortisol level is being
measured multiple times and it could helps to identify more clearly on the level of
HPA activation, since the current theory of stress and memory in human are largely
Social stress and memory 27
dependent on the factor of cortisol increase. With this measurement, we can do more
comparison with the result of many other studies which using drugs to elevate the
cortisol level in human being. It can isolate the ANS activation factor and helps us to
have a better understanding in how stress influence the memory. It can help to answer
the question of “Do stress response (including ANS activation and HPA activation)
impair memory, or only cortisol impairs memory.”
Several improvements can be made in this experiment. Firstly, in choosing the
participants, none of the participant should have any relationship with the
experimenter before the experiment started. It can make sure none of the participant is
familiar with the judges or the experimenter, which can greatly reduce the stressor
strength. Secondly, a more standard TSST procedure should be used, which involve a
switch room procedure during the beginning of the public speech. Multiple judges are
also recommended in the public speech task. Thirdly, multiple measurement of
salivary free cortisol through out the experiment can helps to monitor the direct
cortisol level in the participant, which is essential to clarifying some of the relevant
hypotheses such as the correlation of cortisol level and memory performance.
Fourthly, as mentioned in the introduction of this report, having the same task used as
stressor (Reading span test) and as a measurement might had potential problem,
which it separate high responder and low responder not by the level of stress they face,
Social stress and memory 28
but by the ability that they currently have in that particular task. For example, if a
participant had remarkable working memory, they might found that the reading span
test was not stressful at all, thus the low responder group might also be the high
working memory group. Testing working memory afterward was not meaningful.
Although the present study did not yield any significant result, the
methodological improvement adopted in this study can helps later study to have a
more precise measurement on working memory performance. In many other similar
studies concerning about stress effect on working memory, digit span was used in
measuring the working memory capacity (Kuhlmann, Piel, & Wolf, 2005), compare
with a more continuous measure, such as the reading span test used in the present
experiment, digit span test cannot reflect the working memory as good as the digit
span test. Future studies should focus on how to measure the working memory
capacity using a more comprehensive method. Brain imaging technology can also be
used in similar experiment to see which area of the brain was affected by the stress
treatment, rather than just using some memory tests to speculate the effect of cortisol
inside the brain. Also, cortisol should not be the only indicator of stress impairment on
memory; other alternatives measurement like the animal studies had suggested should
be adopted in human study by an ethical way.
Social stress and memory 29
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Appendix
Table 1
Means and Standard Errors for PANAS Scores
Experimental condition Control condition
Positive affect measure
1 29.64 ± 1.44 31.82 ± 1.21
Positive affect measure
2 29.55 ± 1.69 32.82 ± 1.02
Positive affect measure
3 28.45 ± 1.23 29.82 ± 1.44
Negative affect measure
1 21.82 ± 2.26 20.55 ± 2.09
Negative affect measure
2 23.55 ± 1.77 19.09 ± 1.44
Negative affect measure
3 18.91 ± 2.00 19.55 ± 2.09
All results are means±SE
Social stress and memory 34
Table 2
Tests of Normality in stress estimator
Group Shapiro-Wilk (W) Statistic df Sig.
SYS1 Control 0.8822 11 0.1109
Experimental 0.8338 11 0.0262 *
DIA1 Control 0.9384 11 0.5020
Experimental 0.9518 11 0.6676
Heart Rate 1 Control 0.9643 11 0.8243
Experimental 0.9396 11 0.5160
SYS2 Control 0.9527 11 0.6789
Experimental 0.9745 11 0.9280
DIA2 Control 0.9602 11 0.7737
Experimental 0.9880 11 0.9947
Heart Rate 2 Control 0.9388 11 0.5065
Experimental 0.9169 11 0.2938
SYS3 Control 0.8106 11 0.0130 *
Experimental 0.9769 11 0.9466
DIA3 Control 0.9259 11 0.3710
Experimental 0.9586 11 0.7539
Heart Rate 3 Control 0.9619 11 0.7956
Experimental 0.9687 11 0.8728
Positive affect measure 1 Control 0.9437 11 0.5649
Experimental 0.9582 11 0.7491
Negative affect measure 1 Control 0.9190 11 0.3101
Experimental 0.8806 11 0.1060
Positive affect measure 2 Control 0.8347 11 0.0269 *
Experimental 0.9353 11 0.4674
Negative affect measure 2 Control 0.9010 11 0.1902
Experimental 0.8625 11 0.0620
Positive affect measure 3 Control 0.8622 11 0.0615
Experimental 0.9410 11 0.5327
Negative affect measure 3 Control 0.8936 11 0.1543
Experimental 0.8605 11 0.0584
Sys is the systolic pressure
Dia is the diastolic pressure
The number 1,2,3 indicate different measure which 1 is the baseline measure, 2 is the measure during stress, 3 is
the measure immediate before mixed recall
* indicate that the p value is lower than 0.05
Social stress and memory 35
Table 3
Means and Standard Errors for stress estimators (physiological measurement)
Experimental condition Control condition
SYS1 122.64 ± 3.56 120.18 ± 2.42
SYS2 130.09 ± 3.62 120.73 ± 2.85
SYS3 123.09 ± 4.74 121.64 ± 6.26
DIA1 79.45 ± 4.06 72.18 ± 2.20
DIA2 81.36 ± 3.59 72.82 ± 2.72
DIA3 78.45 ± 2.38 68.00 ± 3.35
Heart Rate 1 72.36 ± 3.25 71.18 ± 4.29
Heart Rate 2 69.55 ± 3.86 70.27 ± 4.01
Heart Rate 3 67.73 ± 3.43 67.64 ± 3.63
All results are means±SE
Sys is the systolic pressure
Dia is the diastolic pressure
The number 1,2,3 indicate different measure which 1 is the baseline measure, 2 is the measure during stress, 3
is the measure immediate before mixed recall
Social stress and memory 36
Table 4
Means and Standard Errors for adjusted delay recall score
Experimental condition Control condition
Adjusted L2 positive 0.191 ± 0.104 0.304 ± 0.088
Adjusted L2 neutral 0.268 ± 0.070 0.428 ± 0.087
Adjusted L2 negative 0.212 ± 0.079 0.387 ± 0.106
Adjusted L3 positive 0.386 ± 0.088 0.440 ± 0.092
Adjusted L3 neutral 0.647 ± 0.116 0.621 ± 0.137
Adjusted L3 negative 0.473 ± 0.104 0.244 ± 0.082
All results are means±SE
*L2 is the recall having 1 day delay, L3 is the recall having 30 mins delay
Social stress and memory 37
Table 5
Tests of Normality in adjusted score of delay recall task
Group Shapiro-Wilk (W) Statistic df Sig.
Adjusted L2 positve Control 0.8677 11 0.0725
Experimental 0.6362 11 0.0001 *
Adjusted L2 neutral Control 0.9610 11 0.7844
Experimental 0.8978 11 0.1735
Adjusted L2 negative Control 0.9183 11 0.3049
Experimental 0.7647 11 0.0032 *
Adjusted L3 positve Control 0.9689 11 0.8757
Experimental 0.9071 11 0.2254
Adjusted L3 neutral Control 0.9634 11 0.8138
Experimental 0.8705 11 0.0786
Adjusted L3 negative Control 0.8501 11 0.0428 *
Experimental 0.9345 11 0.4579
L2 is the recall having 1 day delay, L3 is the recall having 30 mins delay
* indicate that the p value is lower than 0.05
Social stress and memory 38
Table 6
Means and Standard Errors for reading span test
Experimental condition Control condition
Reading Span 1 Total score 13.36 ± 0.68 12.55 ± 1.05
Reading Span 2 Total score 16.55 ± 0.76 16.45 ± 0.79
All results are means±SE
*Reading span 1 was tested during TSST, reading span 2 was tested after the mixed recall
session
Social stress and memory 39
Table 7
Tests of Normality in reading span score
Group Shapiro-Wilk (W) Statistic df Sig.
Reading Span 1 Control 0.9215 11 0.3312
Experimental 0.9441 11 0.5694
Reading Span 2 Control 0.9544 11 0.7002
Experimental 0.9525 11 0.6758
Reading span 1 was tested during TSST, reading span 2 was tested after the mixed recall session