Sleep, 16(2): 128-136
© 1993 American Sleep Disorders Association and Sleep Research Society
Attention, Stress and Negative Emotion in Persistent
Sleep-Onset and Sleep-Maintenance Insomnia
William F. Waters, Serrhel G. Adams, Jr., Paul Binks and Paula Varnado
Department of Psychology, Louisiana State University, Baton Rouge, Louisiana, U.S.A,
Summary: This study investigated the relation of negative emotions, attention and stress to sleep parameters in
insomniacs. It also assessed whether sleep-onset insomniacs differ from sleep-maintenance/mixed insomniacs in
the relations of these variables to sleep parameters. Fourteen sleep-onset insomniacs, 13 sleep-maintenance or mixed
insomniacs and 13 normal sleepers were recruited using two sequential questionnaires. The groups differed significantly on diagnostically relevant sleep parameters, assessed over I week by sleep diary. After completing standard
anxiety, anger and depression inventories, subjects participated in two laboratory procedures during which electrophysiological responses were recorded: orienting response habituation and emotional stress elicitation. The 28
significant correlations of sleep parameters with emotion, habituation and stress measures averaged r = 00415.
In multiple regression analyses, emotion, attention and stress variables accounted for an average of 41 % of the
variance in sleep parameters (mean R = 0.64). Discriminant function analysis using these variables correctly classified
66% of the subjects into the three groups. It was concluded that negative emotions, stress responsiveness and
attentional factors interact to influence insomnia. Key Words: Negative emotion-Emotional stress-Attention/
orienting response habituation-Sleep-onset insomnia-Sleep-maintenance insomnia.
Although the specific nature of the relationship between emotion and sleep parameters has not been thoroughly explored, a number of studies have found greater anxiety and arousal in subjects who complain of
insomnia than in normal sleepers (1-5). Similarly, there
have been a number of studies that have shown an
association between depression and insomnia (5-8).
Studies have shown that stress and anxiety affect
certain aspects of sleep with some consistency. For
example, the first night of sleep in subjects participating
in laboratory sleep research tends to be fragmented.
This has been attributed to the stress and anxiety evoked
by the novel research situation (9-12). In addition, a
longitudinal study of normal sleepers showed significant decreases in Stage 4 sleep and significantly increased spontaneous electrodermal activity on nights
preceded by stressful events during the day (13).
Numerous studies have found a significant relation
between stage of sleep and arousability, with arousability decreasing from nonrapid eye movement
(NREM) Stage 1 to NREM Stage 4. However, the same
studies did not find consistent differences in arousaAccepted for publication November 1992.
Address correspondence and reprint requests to William F. Waters, Ph.D., Department of Psychology, 236 Audubon Hall, Louisiana State University, Baton Rouge, Louisiana 70802, U.S.A.
bility between rapid eye movement (REM) and NREM
sleep (14-18). There also are data demonstrating a relation between stage of sleep and the reaction time to
simple stimuli presented during sleep, with reaction
time increasing from REM and NREM Stage 1 through
Stage 4 (19-21). Given the association between stage
and depth of sleep and resistance to awakening, the
reduction in slow wave sleep associated with presleep
stress may be particularly significant for sleep-maintenance insomnia.
Haynes et al. (4) investigated stress and sleep arousal
thresholds in psychophysiological insomniacs, subjective insomniacs and noninsomniacs. They found that
auditory awakening thresholds were related to presleep
heart rate, but not to any other stress measure, including life events and state anxiety inventory scores. The
groups were not differentiated on the basis of arousal
threshold. They did, however, find that a number of
their stress variables were related to latency to return
to sleep. It should be noted that the Haynes et al.'s
study had two important limitations. First, the hypotheses were tested on subjects napping during the
day. Second, only 10 psychophysiological insomniacs
participated in the study. Earlier studies of the relation between stress and sleep arousal threshold found
subjective reports ofless satisfying sleep and objective
indices of poorer sleep on nights when arousal thresh-
128
ATTENTION, STRESS AND NEGATIVE EMOTION IN INSOMNIA
old was low (22), but no differences between successful
sleepers and poor sleepers (22,23).
The awakening threshold research has not established that attentiveness to stimulation determines
variations in the quality or quantity of sleep. The elicitation and habituation of the orienting response have
not been used to assess the potential relations between
attention and sleep. The orienting response is a physiologically recordable set of responses that reflects the
activity of central nervous system (eNS) processes that
mediate attention and arousal. The orienting response,
as manifested by elicited electrodermal activity, peripheral vasomotor constriction, heart rate deceleration and alpha blocking, has been consistently associated with the shift of attention to a novel or a
consequential stimulus. With repeated presentation of
a stimulus, the orienting response will decrease. This
is known as habituation. When a different stimulus is
presented, an orienting response to that stimulus will
occur. This response also increases the likelihood of
eliciting an orienting response to a subsequent repetition of the habituated stimulus. This is called dishabituation. After a period of time, the orienting response
can reappear upon presentation of a habituated stimulus. This is known as spontaneous recovery (24). The
elicitation, habituation and dishabituation of the orienting response may be considered indices of an individual's state of attentiveness or of attentiveness as
an individual trait (25).
It is necessary to define the relation of both emotion
and attention to psychophysiological insomnia because
the primary theory holds that the eNS and autonomic
nervous system (ANS) arousal mechanisms that are
activated by negative emotion-provoking and attention-provoking stimuli must be inhibited to permit
sleep onset and sleep maintenance (26). A reasonable
hypothesis is that individuals who do not effectively
screen out extraneous stimulation, due to deficient orienting response habituation or to hypersensitive orienting response elicitation, are vulnerable to excessive
eNS arousal that inhibits the eNS processes necessary
for sleep. The sleep initiation and recovery processes
seem particularly vulnerable to interference from external stimulation and internal stimulation generated
by the emotion and/or attention elicited by the day's
events or by future events.
The present study was designed to explore the impact
that negative emotion, stress and attention and habituation to novel stimuli have on sleep. This study investigated: (1) the relations between self-report measures of the negative emotions offear/anxiety, sadness/
depression, and anger/hostility and self-reported sleep
parameters; (2) the relations between attention and
habituation (measured via electro physiological recordings of orienting response elicitation, habituation,
129
dis habituation and spontaneous recovery) and self-reported sleep parameters; (3) the relations between electrophysiological measures recorded under stressful
. conditions and self-reported sleep parameters and (4)
differences in the emotional and psychophysiological
variables between persistent psychophysiological insomniacs presenting with sleep-onset or sleep-maintenance difficulties.
METHODS
Subjects
Subjects were 40 undergraduates from Louisiana
State University (29 females and 11 males; mean age
= 22.4, SD = 6.7). All subjects were volunteers and
gave informed consent prior to participation in the
study. The subjects were separated into two clinical
groups and one control group using a multilevel screening process. Subjects reporting problems with initiating
or maintaining sleep were additionally screened to rule
out poor sleep hygiene and medical or psychiatric causes of insomnia. Screening procedures are described below.
Groups
Control group (n = 13). Subjects in this group reported no difficulties initiating or maintaining sleep.
They were randomly selected from a group of students
reporting that they would be willing to participate in
a research project on insomnia ..
Sleep-onset insomnia group (n = 14). Subjects in this
group reported taking 30 minutes or longer to fall asleep
for 4 or more nights a week, for a period of at least 4
weeks.
Mixed insomnia group (n = 13). Subjects in this
group reported either sleep-maintenance problems or
sleep-maintenance problems coupled with sleep-onset
problems. Sleep-onset insomnia was defined as above.
Subjects with sleep-maintenance problems reported one
awakening > 30 minutes or two or more awakenings
of 2: 5 minutes summing to at least 40 minutes. The
awakenings had to be after sleep onset and were not
the final awakening for the day. The awakenings had
to occur on 4 or more nights per week, for a period of
at least 4 weeks. Although not a pure sleep maintenance
insomnia group, this group did display frequent and
lasting awakenings from sleep.
The above inclusion and exclusion criteria led to the
inclusion of subjects who met the criteria for mildmoderate, sub-acute psychophysiological insomnia, as
defined by The International Classification of Sleep
Disorders (27).
Sleep, Vol. 16, No.2, 1993
130
WATERS ET AL.
Apparatus
A subject sat in a sound-attenuated, electronically
shielded room. The psychophysiological recording
(Grass Model 7D polygraph) and communications
equipment was located in an adjacent room.
Vasomotor response was recorded continuously using a photoplethysmograph attached to a subject's
middle finger of the right hand. As mentioned above,
vasomotor response is one aspect of the orienting response. Vasomotor response yielded information regarding the amount of blood in the digit. A bigger
vasomotor response indicates greater blood flow to the
digit, which is associated with less arousal (28).
Skin resistance was recorded continuously using
electrodes taped to the palmer surfaces of the distal
phalanges of the index and middle fingers of the left
hand. Skin resistance is a measure of electrodermal
activity, which, as mentioned above, is another aspect
of the orienting response. Electrodermal activity is positively associated with greater sweating, which, in turn,
is indicative of higher arousal (28).
Heart rate was recorded continuously using electrodes located on the ventral side of each forearm.
Forehead electromyogram (EMG) was recorded continuously using electrodes attached 1 inch above each
eyebrow, centered above the pupil of the eye with gaze
forward.
Procedure
Before testing, all subjects completed the initial
screening questionnaire used to place subjects in groups
and to rule out subjects whose insomnia was due to
poor sleep hygiene, other sleep disorders, medical disorders or psychiatric disorders. In this screening instrument, subjects were asked questions about their
sleep hygiene, symptoms of other sleep disorders, prior
or current psychiatric contact and prior or current
medical disorders. Next, all subjects meeting criteria
completed daily sleep diary forms at home for one
week. The daily sleep diary was a structurally modified
form (with identical content) of the Lacks Daily Sleep
Diary (29). This measure has demonstrated adequate
reliability and validity (30).
Subjects completed the Beck Depression Inventory
(BDI) (31), the Novaco Provocation Inventory (NPI)
(32), and the State-Trait Anxiety Inventory (ST AI) (33).
Subjects were randomly assigned to complete these
measures either pre- or post-psychophysiological recording. Twenty subjects received the measures prior
to physiological recording and 20 received the measures after physiological recording. For psychophysiological recording, the subject was seated in a soundattenuated electronically shielded room and electrodes
Sleep. Vol. 16. No.2. 1993
and transducers were attached for the recording session. After checking all electrode connections, the subject was instructed to relax and to listen to a taped
. recording. The tape recording began with a description
of the experimental procedures. Following this, the
subject was told to relax, and a polygraphic recording
of the first 3-minute baseline began.
At the end of the first baseline period, the subject
was told that a series of tones was to follow. The subject
was instructed that he/she was to listen to the tones
and that nothing else was required. This second testing
period consisted of orienting response habituation,
dishabituation and spontaneous recovery to the tone.
The subject was presented with 10 identical tones (habituation tones). Twenty seconds after the tenth habituation tone, the subject was presented with a dish abituation stimulus (a buzz). This was followed 20
seconds later by a dishabituation probe, an eleventh
presentation of the habituation tone. The last tone was
presented 2 minutes after the dishabituation stimulus
and it was identical to the habituation tones. At the
conclusion of the tones, the subject was told to relax
again. This constituted the second baseline period.
The last experimental period began with a description of and instructions for taking an oral intelligence
test. This test consisted of 25 items taken from the
Quiz Electrocardiogram (Quiz EKG) (34), a reliable
method of stress elicitation (35). The questions are
sufficiently difficult to ensure a large number of errors
if the time allocated for answers is short (5-10 seconds
is recommended; 5 seconds in the present study). The
instructions lead the subject to believe that performance is linked to intellectual ability. Because a substantial number of failures are certain, it is considered
a stressful experience. No feedback was provided during the procedure, but the subject was informed that
test results and interpretations would be available at
the end of the experimental session. At the conclusion
of the Quiz EKG, the subject was disconnected and
debriefed.
Data reduction and analysis
Vasomotor response was the mean peak-to-trough
amplitude of all pulses during a scoring interval. Heart
rate was the mean cardiotachograph reading during a
scoring interval, expressed in beats per minute (bpm).
Forehead EMG was assessed as the rate of accumulated
muscle potential.
Electrophysiological measures were: (a) skin conductance amplitude during baseline and Quiz EKG,
(b) vasomotor pulse amplitude during baseline and
Quiz EKG, (c) heart rate during baseline and Quiz
EKG, (d) integrated EMG during baseline and Quiz
ATTENTION, STRESS AND NEGATIVE EMOTION IN INSOMNIA
TABLE 1.
Descriptive statistics/or emotional self-report inventory variables
Onset
Mean (SD)
Mixed
Control
Mean (SD) Mean (SD)
STAr-Sa
41.1 (11.2)
44.1 (8.8)
33.4 (8.1)
F = 4.410,
p> 0.05
STAr- T"
44.1 (10.7)
47.5 (10.7)
37.5 (9.5)
F = 4.4,
p> 0.05
BDl'
10.2 (11.4)
13.0 (8.2)
6.2 (5.3)
F= 1.890,
p> 0.05
NPId
296 (41)
278 (34)
247 (41)
F=5.411,
p < 0.01
State Trait Anxiety Inventory-Stage.
State Trait Anxiety Inventory-Trait.
c Beck Depression Inventory.
d Novaco Provocation Inventory.
TABLE 2. Group differences in sleep diary self-report variables. Different letters (a. b. c) indicate differences between
means
Variable
Group
Mean
'22.11 minutes
'26.57 minutes
b8.97 minutes
SOU
Onset
Mixed
Control
NOWASOc
Onset
Mixed
Control
WAsor
Onset
Mixed
Control
b6.29 minutes
'32.45 minutes
b4.31 minutes
TST"
Onset
Mixed
Control
'434.04 minutes
b436.41 minutes
'411.37 minutes
DrFFh
Onset
Mixed
Control
a
h
131
bO.65
'1.55
bO.58
'2.39
'2.44
bl.61
F
SD
11.79
21.76
3.57
p
5.291 0.0095
0.81
0.45 10.236 0.0003
0.49
0.71
22.69 16.718 0.0001
5.21
45.13
48.22
39.15
1.274 0.2916
0.65
0.64
0.40
8.502 0.0009
EKG, (e) number of skin conductance responses/min0.48
Onset
'2.62
ute during baseline and Quiz EKG, (t) number oftrials QUAL'
0.54 13.686 0.0001
Mixed
'2.80
bl.80
Control
0.56
to habituation of the skin conductance orienting re0.76
Onset
'2.55
sponse, (g) mean amplitude of the skin conductance
0.61 7.045 0.0026
'2.66
orienting response during habituation, (h) skin con- TENSIONj Mixed
bl.77
0.60
Control
ductance response amplitude to the dishabituating
0.46
Onset
'2.73
stimulus, (i) skin conductance orienting response am- MENTAL' Mixed
0.77 10.726 0.0002
'3.14
b2.00
plitude to the post-dishabituating stimulus tone and
Control
0.60
U) skin conductance orienting response amplitude to
d Sleep onset latency.
, No. awakenings after-sleep onset.
the spontaneous recovery test tone.
r Mean minutes awake after sleep onset.
The emotional self-report inventory variables were
Total minutes asleep.
State-Trait Anxiety Inventory, State (STAI-S); Stateh Difficulty falling asleep. (\ = low to 5 = high)
, Quality of sleep. (I = high to 5 = low)
Trait Anxiety Inventory, Trait (STAI-T); Beck De, Somatic tension prior to sleep. (\ = low to 5 = high)
pression Inventory (BDI) and Novaco Provocation
, Mental activity prior to sleep. (\ = low to 5 = high)
Inventory (NPI). Means, standard deviations and F
ratios are presented in Table 1. None of the group
means was indicative of pathological levels of depres- Quiz EKG and the initial resting baseline for all subsion, anxiety or anger.
jects (mean difference = 2.24, SO = 3.19, t = 4.32, p
The sleep event measures from the daily sleep diary < 0.01). The mean difference in heart rate between the
were mean ratings of sleep-onset latency, number of periods also was significant (4.90 beats/minute, SO =
awakenings post-sleep onset, mean duration of post- 10.03, t = 3.09, p < 0.01), as was the mean difference
sleep onset awakenings and total minutes sleep. The in vasomotor response amplitude (-31.51 ",V, SO =
sleep rating scale measures selected for this study were 71.04, t = -2.70, p < 0.01). It was concluded that the
mean ratings of difficulty falling asleep, quality of sleep, Quiz EKG was an effective stressor.
somatic tension prior to sleep onset and degree of menThe three groups differed in the expected directions
tal activity prior to sleep onset. These four qualitative on the variables that reflected the selection (inclusion)
sleep variables were measured using a five point (1-5) criteria. The subjects reported the same sleep patterns
Lickert-type scale. The other daily sleep diary rating for the seven nights of sleep diary recording that they
scales were redundant in content with those selected. reported in the screening questionnaires. The groups
Therefore, they were not included in analyses.
differed significantly in time to sleep onset, number of
awakenings and time awake after sleep onset, but not
total minutes of sleep. The self-report sleep ratings for
difficulty
falling asleep, quality of sleep and somatic
RESULTS
tension prior to sleep showed the same pattern of group
Before the data could be interpreted, it was necessary differences, with insomnia subjects indicating signifito determine if the Quiz EKG was an effective stressor. cantly more impaired sleep than controls. The means,
t tests indicated a significant difference in number of standard deviations, F ratios and levels of significance
skin conductance responses per minute between the are presented in Table 2.
g
Sleep. Vol. 16. No.2. 1993
WATERS ET AL.
132
TABLE 3. Significant Pearson correlations of sleep variables with electrophysiological variables and emotion self-report
variables across groups
Minutes
asleep
SCAMP-BLa
r = -0.358
p
=
0.023
SCAMP-HABh
Difficulty
falling asleep
r = 0.411
p
=
0.008
r = -0.383
p
=
0.015
r = 0.335
p
p < 0.001
p
=
0.007
r
p
=
=
0.309
0.052
r = 0.398
p=O.OIO
r = 0.361
p
p
0.021
Mental
activity
r = 0.344
p
=
0.029
r = 0.447
p
=
0.003
r = 0.328
p
=
0.038
=
0.021
r = 0.359
p
r=0.471
p = 0.002
=
0.029
r = 0.422
p
=
0.007
=
r = 0.437
p
=
0.005
r = 0.488
r = 0.470
p
STAI-Si
=
Tension
level
r = 0.377
VMR-Qzr
BDP
0.034
r = 0.417
VMR-BU
NPIg
=
r = 0.562
TRIAL-HAB'
SCAMP-QZd
Quality of
sleep
0.002
p
=
0.001
r = 0.383
p
=
0.016
r = 0.438
p
=
0.005
r = 0.479
r = 0.367
r = 0.470
r = 0.433
p = 0.001
p = 0.019
p
p
=
0.002
=
0.005
Skin conductance response amplitude-fluctuations during baseline.
h Skin conductance response amplitude-orienting response during habituation.
c Number of trials to skin conductance response habituation.
d Skin conductance response amplitude-fluctuations during stress.
Peripheral vasomotor pulse amplitude-during baseline .
.r Peripheral vasomotor pulse amplitude-during stress.
g Novaco Provocation Inventory
h Beck Depression Inventory.
i State Trait Anxiety Inventory-State.
a
C
Correlations
Because prior research in the area of attention and
emotional reactivity in insomnia is scant, there were
no means of making appropriate a priori decisions
regarding which variables to include in further statistical analyses. Therefore, Pearson product-moment
correlations of the independent variables (electrophysiological measures and emotional self-report
scores) with the dependent variables (sleep events and
rating scales) were calculated. The correlation matrices
were then inspected in order to determine which variables would be used in further analyses. The significant
correlations and their levels of statistical significance
are presented in Table 3.
The independent variables selected for further statistical analyses were those that were both less correlated with each other and better correlated with the
dependent variables. The dependent variables selected
were those best and most often correlated with the
independent variables.
The selected electrophysiological variables (independent variables) were mean amplitude of the skin
conductance response recorded during habituation,
number of trials to habituation of the skin conductance
response, skin conductance response amplitude to the
Sleep. Vol. 16, No.2, 1993
dishabituating stimulus, mean skin conductance response amplitude during Quiz EKG, vasomotor pulse
amplitude during Quiz EKG and heart rate during Quiz
EKG. The emotion self-report inventory variables (independent variables) was STAI-S, BDI and NPI scores.
The dependent variables were mean ratings of total
minutes asleep, difficulty falling asleep, quality of sleep,
somatic tension prior to sleep and mental activity prior
to sleep.
Multiple regression analyses
The selected independent variables (electrophysiological measures and emotion self-report scales) were
entered into forward stepwise multiple regression analyses to predict the selected dependent variables (sleep
events and rating scales). Multiple regression analyses
were chosen because all independent and dependent
variables were continuous in nature. The object was
to determine which electrophysiological and emotion
variables were the best predictors of the levels of the
sleep variables. Statistically significant multiple correlations (R) were found for each sleep rating scale and
for total minutes asleep.
An equation including mean skin conductance re-
ATTENTION, STRESS AND NEGATIVE EMOTION IN INSOMNIA
sponse amplitude during Quiz EKG alone predicted
total minutes asleep (R = 0.449, p < 0.01), accounting
for 20% of the variance in the prediction. An equation
including mean amplitude of the skin conductance response during habituation, heart rate during Quiz EKG,
NPI and STAI-S predicted difficulty falling asleep (R
= 0.798, p < 0.001), accounting for 64% of the variance. An equation including mean amplitude of the
skin conductance response during habituation, NPI and
heart rate during Quiz EKG predicted mean ratings of
quality of sleep (R = 0.683, p < 0.001), accounting for
47% of the variance. An equation including the BDI,
mean amplitude of the skin conductance response during habituation, skin conductance response amplitude
to the dishabituating stimulus, NPI and vasomotor
pulse amplitude during Quiz EKG predicted mean ratings of somatic tension prior to sleep onset (R = 0.761,
p < 0.001), accounting for 58% of the variance. An
equation including BDI, NPI and heart rate during
Quiz EKG predicted mean ratings of degree of mental
activity prior to sleep (R = 0.558, p < 0.01), accounting
for 31 % of the variance.
The critical predictors of the sleep variables were
mean amplitude of skin conductance response during
Quiz EKG, mean amplitude of skin conductance response during habituation, STAI-S, NPI and BDI.
Heart rate during Quiz EKG, skin conductance response amplitude to the dishabituating stimulus, number of trials to habituation of the skin conductance
orienting response and vasomotor pulse amplitude
during Quiz EKG contributed less often and/or less
importantly. None of the equations or Rs changed when
EMG recorded during Quiz EKG was added to the
regression analyses. Across the analyses, the average
R was 0.639, accounting for 41% of the variance.
A modified Herzberg shrinkage formula was used in
order to adjust R2 for shrinkage and to correct for preselection of predictors from a larger set of variables
(36). The formula provides an estimate of the population R2 while correcting for capitalization on chance
in preselecting predictors from a larger set of potential
predictors. Using this formula, the selected independent variables were not able to predict total minutes
of sleep or mental activity prior to sleep. However, the
equation including mean amplitude of the skin conductance response during habituation, heart rate during Quiz EKG, NPI and STAI-S still predicted difficulty falling asleep, with an adjusted R2 = 0.47 (47%
of the variance). The equation including mean amplitude of the skin conductance response during habituation, NPI and heart rate during Quiz EKG still predicted mean ratings ofquality of sleep, with an adjusted
R2 = 0.22 (22% of the variance). The equation including
the BDI, mean amplitude of the skin conductance response during habituation, skin conductance response
133
amplitude to the dishabituating stimulus, NPI and vasomotor pulse amplitude during Quiz EKG still predicted mean ratings of somatic tension prior to sleep
onset, with an adjustedR2 = 0.38 (38% of the variance).
Discriminant function analyses
Because group membership is a not a continuous
variable, discriminant function analyses were used to
classify the research subjects as controls, sleep-onset
insomniacs or mixed insomniacs on the basis of their
independent variable scores. The optimal number of
independent variables was five (for 40 subjects). The
following five variables were selected: mean amplitude
of skin conductance response during Quiz EKG, mean
amplitude of the skin conductance response during habituation, vasomotor pulse amplitude during Quiz
EKG, STAI-S and NPI. These variables accurately
classified 66% of the subjects as belonging to their
proper group. Chance classification was 33%. Ten of
the 13 control subjects were classified correctly (76.9%),
eight of the 12 mixed insomniacs were classified correctly (66.7%) and six of the 11 sleep-onset insomniacs
were classified correctly (54.5%).
Misclassification involved the assignment of three
sleep-onset insomniacs to the mixed insomnia group
(27%). Two mixed insomniacs were misclassified as
sleep-onset insomniacs (17%). Three control subjects
were classified as insomniacs (23%) and four insomniacs were classified as controls (17%).
DISCUSSION
The current data support the division of subjects into
three groups. The three groups differed on all sleep
variables except for total minutes asleep. All three
groups reported approximately the same amount of
sleep per night averaged across the seven nights. The
sleep-onset and mixed insomniacs took longer to attain
sleep, reported more trouble falling asleep, poorer sleep
quality, more pre-sleep somatic tension and mental
activation and poorer functioning the following day
than the control subjects. The mixed insomniacs woke
up more often and were awake for longer times after
initial sleep onset than the sleep-onset insomniacs or
the controls. It appears that the subjects slept in a
manner consistent with initial self-reports and consistent with the inclusion criteria. The fact that the groups
did not differ in total sleep time is understandable given
the nature of the population sampled. Undergraduate
university students with sleep difficulties have more
flexible schedules than persons who work in structured
situations. Therefore, they are able to go to bed earlier
or stay in bed longer to compensate for prior episodes
of poor sleep. Regardless of their scheduling flexibility
Sleep, Vol. 16, No.2, 1993
134
WATERS ET AL.
and equal sleep time, the insomniacs' sleep was less
satisfying.
The present data are consistent with past research
(1-8) in establishing the relation between emotional
arousal and sleep. Each of the emotion self-report measures correlated significantly with most of the sleep
rating scales. Across all subjects, anxiety (state), depression and anger correlated well with all four sleep
rating scales.
There were no statistically significant differences
among the three groups in emotional self-report measures, psychophysiological response to the stressor or
attentional measures. Yet, each of these measures correlated significantly and well with a variety of sleep
variables. The control group had only five significant
correlations compared to 17 for the mixed insomnia
group and 16 for the sleep onset insomnia group. The
insomniac subjects were not more responsive in emotional, stress or attentional modalities than normal
sleepers. Yet, emotional, stress and attentional factors
were related to sleep in a greater degree for insomniacs
than for normal sleepers. A difference between persistent psychophysiological insomniacs and normal
sleepers may be that insomniacs' sleep/wake systems
are more responsive to emotional, stress and novel
attention-provoking stimuli than are those of normal
sleepers. This may be an instance of individual-response stereotypy (37,38), in which different persons
respond to the same stimulus with different hierarchical patterns of physiological response. Therefore, insomniacs may have a sleep/wake system that is less
robust against disruptions from emotion, stress or novel stimuli. This is a point for further investigation.
Increased electrodermal activity was consistently associated with poor sleep ratings as hypothesized. However, the vasomotor response data did not support the
initial hypothesis. Vasomotor response amplitude correlated negatively with total sleep time. Thus, decreased vasomotor response amplitude, which indicates increased arousal, was associated with increased
sleep time instead of decreased sleep time as hypothesized. Similarly, vasomotor response amplitude was
positively correlated with the number of awakenings
and sleep quality ratings, again the opposite of what
was hypothesized. Therefore, decreased vasomotor response amplitude (arousal) was associated with fewer
awakenings and lower (better) sleep quality ratings.
The discrepancy may be an instance of autonomic nervous system directional fractionation of response (39).
In this situation, two psychophysiological measures
that typically covary across different conditions may
react independently under other conditions. This implies that psychophysiological variables may serve different purposes under different conditions. Hence, they
are sometimes fractionated, rather than always unified.
Sleep. Vol. 16. No.2. 1993
The electro physiological measures recorded during
the emotionally arousing stress situation (the Quiz
EKG) correlated significantly with many of the sleep
measures: time asleep, difficulty attaining sleep, quality
of sleep and somatic tension at bedtime. There was a
solid relation between psychophysiological emotional
response variables and sleep variables across subjects.
However, inspection of the data indicated that there
were different patterns of correlation among the groups,
with different psychophysiological variables being related to different sleep variables for each group.
The high correlations across groups of habituation,
dishabituation and spontaneous recovery of the orienting response with sleep variables provide some very
interesting information. These data indicate that the
hypothesized relation between attention and insomnia
exists. Habituation correlated well with sleep quality,
difficulty falling asleep and somatic tension prior to
sleep. Thus, greater attentional arousal was related to
less adequate sleep. Again, the correlations within the
groups of subjects showed different patterns among the
groups, with different habituation variables being related to different sleep variables for each group.
The high across-group correlations of the emotional
self-report variables supported the hypothesized relation between emotion and insomnia. Anger, depression and anxiety correlated well with difficulty falling
asleep, quality of sleep, somatic tension prior to sleep
and mental activity prior to sleep. Again, the correlations within the groups of subjects showed different
patterns among the groups.
The meaning of the different within-group correlations for the etiology and/or maintenance of the different forms of insomnia cannot be determined from
the present data because of the small number of subjects in each group, the absence of statistically significant differences between insomnia group means and
the lack of an apparently meaningful pattern among
the variables. Nonetheless, the different within-group
correlations are of significant heuristic value because
they suggest that stress, habituation/attention and
emotional state variables may have different effects on
different aspects of sleep. It is another point for further
investigation.
The prediction of the sleep variables using the emotion self-report and the electrophysiological variables
yielded an average uncorrected R of 0.64, account\ng
for 41 % of the variance. All of the sleep variables were
predicted effectively. Statistical control for both
shrinkage and preselection significantly reduced the R/s
(2 of 5 became nonsignificant). However, the selected
correction procedures represent one of the most conservative estimates of R2. Although the corrections underscore the need for further study concerning the relationship between stress, emotional and attentional
ATTENTION, STRESS AND NEGATIVE EMOTION IN INSOMNIA
variables and total sleep time and mental activity prior
to sleep, they also point to the robustness of the relationship between stress, emotional and attentional
variables and difficulty falling asleep, quality of sleep
and somatic tension prior to sleep.
Using the five chosen predictor variables, the discriminant function analysis classified subjects' group
membership with 66% accuracy, double the chance
rate of 33%. The interactions among stress, emotional
and attentional variables can be seen as effectively discriminating insomniacs from good sleepers and even
insomniacs with sleep-maintenance problems from
those having only sleep-onset problems. Although correlational data do not necessarily indicate causation,
the implication is that the predicting and discriminating variables may playa role in the cause and course
of these disorders. Further research is needed to address the issue of what causal roles these variables may
play in insomnia.
The present data provide evidence for the importance of stress, emotional and attentional variables in
both sleep-onset and sleep-maintenance insomnia. Admittedly, the data are based on a daytime analog experiment, limiting the generalizability as to what insomniacs might experience physiologically at night.
However, emotion self-report inventory data, electrophysiological emotional stress response data and electrophysiological attention data were significantly related to, and predictive of, reported sleep variables.
While future research should focus on physiological
variables measured at night, the results from the current study provide a strong base for further investigations.
The single most influential variable in this study was
clearly skin resistance amplitude during habituation.
It is a correlate of attentional shift to a novel stimulus
and may be said to indicate the degree to which a
stimulus captures attentional resources. The present
data indicate that sensitivity to novel stimulation is
correlated with report of delayed sleep onset and with
report of unrestful and poor quality sleep. The implication is that individual differences in orienting response habituation are significant factors in determining the degree of sleep quantity and quality.
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