Department of Applied Social Studieslbms03.cityu.edu.hk/oaps/ss2007-4708-lcm278.pdfsystem will cause a number of body changes, those changes is called fight-or flight response, which

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


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.


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.


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


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


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,


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.


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


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


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,


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


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


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


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


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


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


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


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


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


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)


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).


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


(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


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


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


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


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,


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.


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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


2 29.55 ± 1.69 32.82 ± 1.02


3 28.45 ± 1.23 29.82 ± 1.44

Negative affect measure

1 21.82 ± 2.26 20.55 ± 2.09


2 23.55 ± 1.77 19.09 ± 1.44


3 18.91 ± 2.00 19.55 ± 2.09

All results are means±SE


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


SYS2 Control 0.9527 11 0.6789


DIA2 Control 0.9602 11 0.7737




SYS3 Control 0.8106 11 0.0130 *


DIA3 Control 0.9259 11 0.3710




Positive affect measure 1 Control 0.9437 11 0.5649


Negative affect measure 1 Control 0.9190 11 0.3101


Positive affect measure 2 Control 0.8347 11 0.0269 *




Positive affect measure 3 Control 0.8622 11 0.0615




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


Table 3

Means and Standard Errors for stress estimators (physiological measurement)


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


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


Table 4

Means and Standard Errors for adjusted delay recall score


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


*L2 is the recall having 1 day delay, L3 is the recall having 30 mins delay


Table 5

Tests of Normality in adjusted score of delay recall task


Adjusted L2 positve Control 0.8677 11 0.0725

Experimental 0.6362 11 0.0001 *

Adjusted L2 neutral Control 0.9610 11 0.7844


Adjusted L2 negative Control 0.9183 11 0.3049

Experimental 0.7647 11 0.0032 *

Adjusted L3 positve Control 0.9689 11 0.8757


Adjusted L3 neutral Control 0.9634 11 0.8138


Adjusted L3 negative Control 0.8501 11 0.0428 *


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


Table 6

Means and Standard Errors for reading span test


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


*Reading span 1 was tested during TSST, reading span 2 was tested after the mixed recall

session


Table 7

Tests of Normality in reading span score


Reading Span 1 Control 0.9215 11 0.3312


Reading Span 2 Control 0.9544 11 0.7002


Reading span 1 was tested during TSST, reading span 2 was tested after the mixed recall session

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