Business Process Management IBM Business Process Manager V8

The Effects of Physiological Stress and Noise on Attention

P.I.: Arsalaan Salehani ([email protected])

Faculty Supervisor: David W. Pittman, Ph.D.

Introduction

In our globalized, fast-paced world of today, we often work under constant amounts of

stress and pressure. It is believed that some level of stress actually enhances our cognitive

abilities, such as memory and attention, while excessive stress impairs cognitive performance.

The Yerkes-Dodson Law (Image 1) is a pictorial representation of this effect, in which an

inverted U-shaped curve depicts the relationship between the level of stress on the x-axis and the

efficiency of performance on a cognitive task on the y-axis (Mendl, 1999).

Image 1: Yerkes-Dodson Law

Till date, many studies have investigated the effects of stress on cognitive abilities such

as memory and attention. For example, acute increases in cortisol have been associated with

decrements in both attention and memory, suggesting that acute stress has negative effects on

select cognitive processes (Vedhara et al., 2000). Paradoxically, this same study also found that

reduced levels of cortisol also resulted in impairments in attention (Vedhara et al., 2000). Thus,

as suggested above by the Yerkes-Dodson Law (Image 1), there appears to be a fine balance

between the beneficial and detrimental levels of stress as measured by its effects on cognitive

capabilities. This phenomenon is particularly pertinent to stressors such as continuous loud

noise, heat, and sleep deprivation. All of these have been found to lead to different types of

errors in tasks measuring attention (Mendl, 1999).

Another hormone implicated in the effects of stress on attention is norepinephrine (NE).

Depletion of NE in monkey and mouse models has resulted in increased distractibility and

working memory deficits (Skosnik et al., 2000). One model for this effect suggests an

interaction between stress-induced NE release and prefrontal cortex (PFC) neurons (Image 2).

As NE is involved in the “fight or flight” response, it is hypothesized that evolutionarily,

organisms facing danger would benefit from widened attentional focus as a result of NE release

from the sympathetic nervous system. Skosnik et al. also suggest that NE facilitates the effects

of cortisol during the stress response (2000). In other words, when cortisol and NE are present in

the system simultaneously, levels of cortisol can be used to predict behavioral measures of

attention. However, baseline levels of cortisol do not affect cognitive abilities because there is

no release of NE to facilitate this effect (Skosnik et al., 2000).

Image 2: Prefrontal cortex

A now classic methodology for measuring attention is the Stroop task. First performed

by J. Ridley Stroop in 1935, this task manipulates the congruence of word color and font color.

In other words, a congruent condition would say the word “red” in red font, whereas an

incongruent condition would say the word “red” in blue font (Image 3). In the most often

repeated version, subjects are instructed to report the font color rather than the word color (i.e.

report blue rather than red in the incongruent condition described above). Subjects’ reaction

times (RT) and accuracies are recorded. An increase in RT and a decrease in accuracy are

expected in the incongruent compared to the congruent condition because the automatic process

of reading is interfering with the non-automatic/controlled process of reporting font color

(Stroop, 1935).

Image 3: Examples of the incongruent Stroop condition

As background information for some of the techniques in the current study, the nervous

system is divided into two divisions, i.e. somatic and autonomic. For our purposes, we will be

focusing on the autonomic nervous system (ANS), which is further divided into the sympathetic

and parasympathetic nervous systems (SNS and PNS, respectively). The SNS controls the “fight

or flight” response by becoming activated in times of physiological stress. One of the effects of

SNS activation is increased sweat production. This, in turn, increases the conductance of the

skin, which can be measured quantitatively as the galvanic skin response (GSR). In addition to

GSR, the current study relies on heart rate (HR) measurements recorded as beats per minute

(BPM).

The purpose of this experiment was to determine any differences in attentional abilities,

GSR, and HR measurements in physiologically stressful and loud versus peaceful noise

conditions. It was hypothesized that the ice bath and loud noise conditions would cause

increased GSR and HR measurements, while the ice bath and peaceful noise conditions would

cause a decrease in RT in the Stroop task, and the ice bath and loud noise conditions would cause

decreased accuracy in the Stroop task.

Methodology

Subjects: Subjects were 12 undergraduate students at Wofford College, ages ranged from 18-22.

Equipment: Equipment used in this experiment included the following items:

The Biopac GSR System and equipment used to measure the galvanic skin response

(Image 4).

The Biopac HR System and equipment used to measure heart rate in beats per minute

(Image 5).

Loud industrial noise audio clip

Peaceful nature noise audio clip

Bucket, towels, cooler, and ice

Online color reading interference Stroop task on laptop

Figure 4: GSR monitors attached to fingers

Figure 5: Electrode setup for HR measurements

Experimental Protocol: Subjects were recruited via email and text message on a volunteer basis.

Subjects signed a consent form that addressed the possible hazards and regulations surrounding

the experiment, in addition to entering them into a drawing for a $20 Pizza Hut gift card as

incentive for participation. All conditions and Stroop task trials were completed while GSR and

HR measurements were being recorded. The control and experimental conditions were no ice

bath and ice bath, respectively. Within each of these conditions, subjects were exposed to a loud

industrial noise and a peaceful nature noise. GSR recordings were made from the left index and

middle finger, and electrodes for the HR measurement were attached as directed in the Biopac

student manual lesson 9 (Image 5). Noise conditions were staggered, in that the control

condition consisted of the loud then peaceful noise conditions, whereas the reverse order of noise

conditions was used in the experimental condition (i.e. peaceful then loud noise). The online

Stroop task was completed using a MacBook Pro laptop, and subjects were instructed to only use

their right index fingers to press the key corresponding to the first letter of the font color of the

word presented in the trial.

The control condition began with a 2-minute pre-test baseline in which the subject was

instructed to relax and remain still. Then, the subject completed 50 trials of the Stroop task

while listening to the loud noise and then 50 trials while listening to the peaceful noise. The

control condition culminated in a 2-minute post-test baseline. The first half of the experimental

condition required the subjects to immerse their right foot in the ice bath, and the second half

required the immersion of the left foot in order to prevent excessive exposure to cold

temperatures solely on one foot. For each of the feet, the experimental condition began with a 2-

minute pre-test baseline, followed by completion of 50 trials of the Stroop task during a noise

condition (peaceful noise for right leg and loud noise for left leg), and finally a 2-minute post-

test baseline.

Stroop reaction time, Stroop accuracy, GSR measurements, and HR recordings were then

analyzed for an interaction between stress and performance on attention tasks. Dependent

variables included GSR measurements, HR recordings, Stroop RT, and Stroop accuracy.

Independent variables included the loud or peaceful noise condition, the no ice bath or ice bath

condition, and the congruency of the Stroop task. A repeated measures analysis of variance

(ANOVA) was performed using SPSS software to analyze the GSR, HR, and Stroop task data.

P-values less than 0.05 were considered statistically significant, however, results with p-values

close to 0.05 have also been included in the results.

Results

GSR

Figure 1: Effects of Experimental and Noise Condition on GSR

As demonstrated by Figure 1, there was an interaction between experimental and noise

condition, 6.835 (1,11), p=0.024, on GSR recordings. Overall, all experimental and noise

conditions led to an increase in GSR activity (as shown by all y-axis values being larger than 1).

0

1

2

3

4

5

6

No Ice,Loud No Ice,Peaceful Ice,Loud Ice,Peaceful

Ch

an

ge

in

GS

R

Experimental and Noise Condition

However, the ice bath condition while listening to peaceful noise led to a significantly smaller

increase in GSR activity as compared to the other experimental and noise conditions.

HR

Figure 2: Effect of Experimental Condition on HR

As demonstrated by Figure 2, there was a main effect of experimental condition, 3.577

(1,11), p=0.085, on heart rate as measured in beats per minute (BPM). The no ice bath condition

led to an increase in heart rate compared to baseline (denoted by 1 on the y-axis), while the ice

bath condition led to a decrease in subjects’ heart rate compared to baseline.

0.85

0.9

0.95

1

1.05

1.1

1.15

No Ice Ice

Ch

na

ge

in

HR

Experimental Condition

Stroop Reaction Time (RT)

Figure 3: Effect of Experimental Condition on Stroop Reaction Time

As demonstrated by Figure 3, there was a main effect of experimental condition, 16.879

(1,11), p=0.002, on Stroop RT. Subjects had a decreased reaction time in the Stroop task when

in the ice bath condition as compared to the no ice bath condition.

Figure 4: Effect of Noise Condition on Stroop Reaction Time

0

200

400

600

800

1000

1200

No Ice Ice

RT

(m

s)

Experimental Condition

840

860

880

900

920

940

960

980

Loud Peaceful

RT

(m

s)

Noise Condition

As demonstrated by Figure 4, there was a main effect of noise condition, 5.678 (1,11),

p=0.036, on Stroop RT. Subjects had a decreased reaction time in the Stroop task when in the

peaceful noise condition as compared to the loud noise condition.

Figure 5: Effect of Stroop Condition on Stroop Reaction Time

As demonstrated by Figure 5, there was a main effect of Stroop condition, 110.078

(1,11), p<0.001, on Stroop RT. Subjects had a much decreased reaction time in the Stroop task

when in the congruent condition as compared to the incongruent condition.

0

200

400

600

800

1000

1200

Congruent Incongruent

RT

(m

s)

Stroop Condition

Figure 6: Effect of Experimental and Noise Condition on Stroop Reaction Time

As demonstrated by Figure 6, there was an interaction of experimental and noise

condition, 47.916 (1,11), p<0.001, on Stroop RT. The no ice bath condition with the loud noise

had the highest reaction time in the Stroop task, followed by the no ice bath condition with the

peaceful noise, then the ice bath condition with the peaceful noise, and finally the ice bath

condition with the loud noise, which had the smallest reaction time in the Stroop task.

Stroop Percent Correct

Figure 7: Effect of Stroop Condition on Stroop Percent Correct

0

200

400

600

800

1000

1200

No Ice,Loud No Ice,Peaceful Ice,Loud Ice,Peaceful

RT

(m

s)

Experimental and Noise Condition

96

96.5

97

97.5

98

98.5

99

99.5

100

100.5

101

Congruent Incongruent

Pe

rce

nt

Co

rre

ct

Stroop Condition

As demonstrated by Figure 7, there was a main effect of Stroop condition, 3.624 (1,11),

p=0.083, on Stroop percent correct. The congruent condition had a greater percentage of correct

answers in the Stroop task as compared to the incongruent condition.

Figure 8: Effect of Experimental and Stroop Condition on Stroop Percent Correct

As demonstrated by Figure 8, there was an interaction of experimental and Stroop

condition, 6.750 (1,11), p=0.025, on Stroop percent correct. The no ice bath congruent condition

had 100% correct answers in the Stroop task, followed by the ice bath congruent condition, then

the ice bath incongruent condition, and finally the no ice bath incongruent condition, which had

the lowest percentage of correct answers in the Stroop task.

Discussion

Based on the work of previous studies, it is believed that stress has an effect on cognitive

abilities, such as memory and attention. According to the Yerkes-Dodson Law, some level of

stress actually enhances the efficiency of specific cognitive abilities, however, excessive stress

impairs these same abilities. Hormones such as norepinephrine (NE) and cortisol have been

95

96

97

98

99

100

101

No Ice,Con. No Ice,Incon. Ice,Con. Ice,Incon.

Pe

rce

nt

Co

rre

ct

Experimental and Stroop Condition

shown to be involved with this phenomenon, with NE likely facilitating cortisol’s effects on

cognitive abilities. Specifically for this study, the effects of physiological stress and noise on

attention were examined. It was hypothesized that the ice bath and loud noise condition would

cause increased GSR and HR measurements, while the ice bath and peaceful noise conditions

would cause a decrease in RT in the Stroop task, and the ice bath and loud conditions would

cause decreased accuracy in the Stroop task.

Based upon the results of this study, the first half of the initial hypothesis with regards to

the GSR measurements was supported. All of the conditions depicted in Figure 1 resulted in an

increase in GSR (as shown by all values for the y-axis being larger than 1), with the ice bath

condition with the peaceful music having the smallest increase. A possible explanation for this

result is a relatively smaller activation of the sympathetic nervous system in the ice bath when

coupled with the peaceful noise condition. It is interesting to note that the no ice bath conditions

actually showed greater increases in GSR than the ice bath condition, which could possibly be

due to the ice lessening the activation of the sympathethic nervous system while the participant

completed the Stroop task.

Based upon the results seen in Figure 2, the first half of the initial hypothesis with regards

to HR measurement was rejected. Rather than causing an increase in HR, the ice bath condition

was shown to actually cause a decrease in HR as compared to baseline levels. Possible

explanations for this result could be the conservation of energy, in which the body’s homeostasis

mechanism is slowing down metabolism as its energy demands are decreased due to exposure to

colder temperatures. If metabolism is slowed down, then the need for nutrients and oxygen as

supplied by the cardiovascular system is decreased, and so HR can slow down in order to

conserve energy. However, it seems somewhat unlikely that immersing only one foot in an ice

bath would lead to such a global effect on HR in this experiment. Thus, other factors could be

involved, such as the limitations of a small sample size and equipment or experimenter error.

Based upon the overall results as seen in Figures 3-6, the second half of the initial

hypothesis with regards to Stroop reaction time was supported. Figure 3 shows decreased

reaction time in the ice bath condition as compared to the no ice bath condition. In addition,

Figure 4 shows the peaceful noise condition resulting in a decreased RT in the Stroop task. The

slight discomfort induced by the ice bath likely motivated subjects to finish their Stroop task

trials quicker, while the peaceful condition likely allowed greater focused attention without the

distraction present in the loud noise condition. Figure 5 shows data replicating the classic Stroop

effect, in which the congruent condition has a decreased RT as compared to the incongruent

condition. When examined together, the no ice bath/ice bath and noise conditions have a

significant interaction to affect RT in the Stroop task. As shown in Figure 6, the ice bath with

loud noise condition actually had the shortest RT followed by the ice bath with peaceful noise.

Based upon this individual graph, the initial hypothesis with regards to RT needs to be qualified,

because the ice bath and loud noise condition, rather than the ice bath and peaceful noise

condition, as predicted in the hypothesis, showed the smallest RT. However, the results for the

two ice bath conditions in Figure 6 are not significantly different from one another, so perhaps a

protocol with a greater number of subjects would show the ice bath and peaceful noise condition

having the smallest RT.

Lastly, based upon the results as seen in Figures 7-8, the initial hypothesis with regards to

accuracy on the Stroop task was qualified. Although none of the noise condition results with

regards to Stroop accuracy were significant or close to significant, Figure 8 shows the interaction

between the no ice bath/ice bath and Stroop conditions and their effect on accuracy. Contrary to

the initial hypothesis, a no ice bath condition, rather than an ice bath condition, showed the

lowest accuracy. However, within the congruent Stroop condition, the ice bath condition showed

lower accuracy on the Stroop task than the no ice bath condition. Based on prior studies and

Figure 7, the Stroop conditions of congruent or incongruent likely have a greater effect on

accuracy than the no ice bath/ice bath condition.

Future studies with a larger sample size may lead to more significant results. In addition,

based on each subject’s individual threshold, varying amounts of ice were added to the ice bath

to elicit slight discomfort but avoid pain. Thus, individual variability is a probable confounding

factor complicating the analysis and determination of the effect of physiological stress on

attention in this experiment. Continued research regarding this interaction could give society

vital information about peak effectiveness under varying stressful conditions in our globalized

and fast-paced world in which productivity is given high priority, such as in the school or work

environment.

References

Mendl M. 1999. Performing under pressure: stress and cognitive function. Applied Animal

Behavior Science. 65: 221-244.

Skosnik P, Chatterton Jr. R, Swisher T, Park S. 2000. Modulation of attentional inhibition by

norepinephrine and cortisol after psychological stress. International Journay of

Psychophysiology. 36: 59-68.

Stroop J.R. 1935. Studies of interference in serial verbal reactions. Journal of Experimental

Psychology. 18: 643-662.

Vedhara K, Hyde J, Gilchrist I.D., Tytherleigh M, Plummer S. 2000. Acute stress, memory,

attention, and cortisol. Psychoneuroendocrinology. 25: 535-549.