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.
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