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Journal of Psychopathology and Behavioral Assessment (JOBA) pp835-joba-464659 April 22, 2003 12:54 Style file version June 25th, 2002
Journal of Psychopathology and Behavioral Assessment, Vol. 25, No. 3, September 2003 ( C
°2003)
Alternative Explanations of Emotional Numbing
of Posttraumatic Stress Disorder: An Examination
of Hyperarousal and Experiential Avoidance
Matthew T. Tull1,2and Lizabeth Roemer1
Accepted October 25, 2002
The mechanisms that underlie the emotional numbing symptoms associated with PTSD are not well
understood. Studies of Vietnam combat veterans have demonstrated that hyperarousal symptoms
predict emotional numbing symptoms more strongly than do other symptoms of PTSD. This study
soughttoextendthesefindingsthroughtheself-reportof170femalesexualassaultsurvivors.The study
also examined whether the relationship between hyperarousal and emotional numbing symptoms was
theresult of therelationship of eachof these toanother variable, thetendencyto engage inexperiential
avoidance.Resultswereconsistentwithandextendedpreviousfindings.Hyperarousalsymptomswere
also found to predict emotional numbing symptoms above and beyond experiential avoidance, as well
as all other symptoms of PTSD.
KEY WORDS: posttraumatic stress disorder; emotional numbing; experiential avoidance; sexual assault.
Individuals suffering from posttraumatic stress dis-
order (PTSD) often experience deficits in the ability to
express and experience emotion, otherwise referred to as
emotional numbing. The Diagnostic and Statistical Man-
ual of Mental Disorders, 4th ed. (American Psychiatric
Association [APA], 1994) describes emotional numbing
as a composite of three symptoms: a markedly diminished
interest in significant activities (Criterion C-4), feelings
of detachment or estrangement from others (C-5), and re-
stricted range of affect (C-6). Though many symptoms of
PTSD (i.e., hyperarousal, intrusive thoughts, and avoid-
ance) are shared with other anxiety disorders, emotional
numbing symptoms are a characteristic feature of PTSD
that distinguish it from the other anxiety disorders (Foa,
Zinbarg, & Rothbaum, 1992).
Research has demonstrated that emotional numbing
symptoms play an integral role in the development and
maintenance of posttraumatic psychopathology. Reports
1Department of Psychology, University of Massachusetts Boston,
Boston, Massachusetts.
2To whom correspondence should be addressed at Department of
Psychology, University of Massachusetts Boston, 100 Morrissey
Boulevard, Boston, Massachusetts 02125; e-mail: matthewttull@
aol.com.
of emotional numbing 1 month following traumatic ex-
posure have been found to be the strongest predictor of
PTSD 5 months later (Harvey & Bryant, 1998). Sever-
ity of emotional numbing symptoms 2 weeks after a
traumatic incident has been found to predict severity of
PTSD 3 months later (Feeny, Zoellner, Fitzgibbons, &
Foa, 2000). Foa, Riggs, and Gershuny (1995) found that
emotional numbing symptoms, as compared to all other
symptoms of PTSD, best distinguished individuals with a
PTSD diagnosis from those without, and Jaycox, Foa, and
Morrall (1998) demonstrated that low levels of emotional
engagement in exposure therapy (which can be concep-
tualized as reflecting emotional numbing) are associated
with poor treatment outcomes. Despite these preliminary
findings, the emotional numbing symptoms associated
with PTSD, as well as the mechanisms underlying these
symptoms, remain largely underresearched and not well
understood.
In the DSM-IV (APA, 1994), emotional numbing
symptoms are included with the avoidance symptoms of
PTSD. Researchers have suggested, however, that emo-
tionalnumbing andavoidancesymptoms ofPTSD are dis-
tinct, with separate mechanisms underlying each. Several
studies analyzing the factor structure of PTSD symptoms
have demonstrated that emotional numbing symptoms
147
0882-2689/03/0900-0147/0 C
°2003 Plenum Publishing Corporation
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148 Tull and Roemer
are separate from avoidance symptoms (e.g., Foa et al.,
1995; King & King, 1994). It has also been suggested
that avoidance behaviors may be driven by strategic psy-
chological processes (i.e., the chronic, active avoidance
of cues that elicit painful emotions) while emotional
numbing may be operating through a more automatic
and passive psychobiological mechanism such as cate-
cholaminedepletion (e.g., vanderKolk,Greenberg,Boyd,
& Krystal, 1985) or conditioned opioid-mediated analge-
sia (Foa et al., 1992).
Litz (1992) has proposed that emotional numbing
may occur as a result of attempts to manage the reex-
periencing and hyperarousal symptoms that accompany
PTSD. He suggests that individuals with PTSD expend
considerable cognitive, behavioral, and emotional energy
in an attempt to manage their hyperarousal symptoms as-
sociated with reexposure. These individuals may reduce
theiremotional resources tosuchan extentthata loss orre-
duction of emotional responsiveness and affective capac-
ity,oremotional numbing, isexperienced. Consistent with
this theory, studies have shown that hyperarousal symp-
tomsofPTSD predict emotionalnumbingsymptoms more
strongly than do active avoidance symptoms (and all other
symptoms associated with PTSD) in samples of Vietnam
combat veterans (Flack, Litz, Hsieh, Kaloupek, & Keane,
2000; Litz et al., 1997).
Litz et al. (1997) have also noted that the demon-
strated relationship between hyperarousal and emotional
numbing may be explained by the relationship of each
of these to another variable—strategic emotional suppres-
sion or, more generally, experiential avoidance. Experien-
tial avoidance is a general term that includes both cogni-
tive and emotional avoidance and refers to any attempt
to alter the form or frequency of internal experiences
(Hayes, Wilson, Gifford, Follette, & Strosahl, 1996). Al-
though experiential avoidance may initially result in re-
duced distress (and thereby be negatively reinforced), the
chronic use of experiential avoidance is likely to have
a paradoxical, negative effect, as attempts to avoid or
alter internal experiences may actually increase the in-
tensity and severity of the very emotions and thoughts
being avoided (Hayes, Strosahl, & Wilson, 1999; see
also Gross & Levenson, 1993, 1997; Wegner, Schneider,
Carter, & White, 1987).
Inregard to therelationship of experientialavoidance
to emotional numbing, a process similar to strategic emo-
tional suppression has been observed among individuals
suffering from PTSD. Roemer, Litz, Orsillo, and Wagner
(2001)found thatVietnamcombatveterans with PTSD,as
comparedtowell-adjustedveterans, reported intentionally
withholding their emotions with greater frequency and
intensity. As a result of this chronic, intentional avoidance
of emotions (i.e., experiential avoidance), individuals
with PTSD may exhibit symptoms of emotional numbing.
As for the relationship between experiential avoidance
and hyperarousal symptoms, hyperarousal may also be
associated with experiential avoidance. The suppression
of emotional expression has been found to result in in-
creased physiological arousal (Gross & Levenson, 1993,
1997), and therefore, it is possible that this form of experi-
ential avoidance among individuals suffering from PTSD
may be accompanied by (or contribute to) hyperarousal
symptoms.3
The above findings suggest an alternative explana-
tion for the relationship between hyperarousal and emo-
tional numbing symptoms of PTSD. Experiential avoid-
ance, rather than hyperarousal, may serve as a major risk
factor for the development of emotional numbing among
individuals who have experienced a potentially traumatic
event. Hyperarousal may only be found to be associated
with emotional numbing as a result of its relationship with
experiential avoidance. That is, hyperarousal may be a
proxy risk factor. According to Kraemer, Stice, Kazdin,
Offord, and Kupfer (2001), any variable (in this case,
hyperarousal) that is associated with a strong risk fac-
tor (experiential avoidance) may also be found to have a
relationship with the same outcome (emotional numbing).
However, in actuality, the relationship between this vari-
able or proxy risk factor and the outcome only exists as a
result of both being associated with the strong risk factor.
This type of third variable relationship is different from
that explained through a mediator or moderator model. In
a mediational model, a variable (i.e., a mediator) is found
to account for the relationship between a predictor and
an outcome (in that the predictor is thought to cause the
mediator, which in turn causes the outcome) whereas in
a moderation model, a third variable (i.e., a moderator)
determines under what conditions another variable will
be associated with an outcome (Baron & Kenny, 1986;
Kraemer et al., 2001). A third variable relationship in-
volving a proxy risk factor, on the other hand, explains a
relationship where a variable is found to be highly asso-
ciated with an outcome only because of its relationship to
3Itisimportant to note that the studies described (i.e., Gross &Levenson,
1993, 1997; Roemer et al., 2001) do not directly examine the construct
of experiential avoidance. Instead, they describe the deliberate with-
holding of emotion or the suppression of emotional expression, which
may not be the same as the avoidance of emotional experience or expe-
riential avoidance (a relatively new and recently researched construct).
However, even though few studies have examined the direct conse-
quences of engaging in experiential avoidance, one can assume that
a similar effect is occurring as that observed among individuals who
withhold the expression of emotion, as withholding expression is likely
an important component of avoiding emotional experience.
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Alternative Explanations of Emotional Numbing 149
another variable strongly associated with that outcome. In
terms of the present study and according to Kraemer and
colleagues’ guidelines (Kraemar et al., 2001) for testing
whether or not a variable is a proxy risk factor, if experi-
ential avoidance is the dominant risk factor for emotional
numbing and hyperarousal is only associated with emo-
tional numbing as a proxy risk factor, then the predictive
ability of hyperarousal should disappear or be weakened
when experiential avoidance is taken into account.
Past studies have not specifically examined whether
the demonstrated relationship between hyperarousal and
emotional numbing symptoms is actually the result of
the relationship of both sets of symptoms to experien-
tial avoidance. Given that an understanding of the pre-
cise nature of the relationship between hyperarousal and
emotional numbing symptoms would likely have impli-
cations for treatment, research investigating the nature of
this relationship is important. Using a sample of female
sexual assault survivors, this study was conducted to ex-
tendthepreviouslydemonstrated findings ofarelationship
between hyperarousal and emotional numbing symptoms
within a sample of combat veterans. This study also ex-
plored whether the association between hyperarousal and
emotional numbing symptoms is best explained by the
relationship of each of these symptoms to experiential
avoidance (i.e., whether hyperarousal serves as a proxy
risk factor in the potential relationship between experien-
tial avoidance and emotional numbing).
METHODS
Participants
This study included 170 female sexual assault sur-
vivors who were a subset of a larger sample (N=924
women) that participated in a questionnaire study at the
University of Massachusetts Boston. Within the current
sample, 49.4% reported experiencing sexual assault in
childhood only, 37.1% in adulthood only, 11.2% in both
childhood and adulthood, and 2.4% reported the experi-
ence of a sexual assault though not the age in which it had
occurred. In terms of frequency of assault, 69.4% reported
experiencing one incident of sexual assault, 11% reported
two separate incidents, 8.2% reported three separate inci-
dents, and 12.2% reported experiencing continuous sex-
ual assault, or greater than three incidents. Participants
ranged in age from 18 to 61 years with an average age of
24 (SD =6.88). The racial/ethnic background of partici-
pants was 59.4% White, 18.2% Black/African American,
6.5%Hispanic, 2.9%Asian, 0.6%Native American, 5.9%
biracial, and 6.5% of another or unspecified racial/ethnic
background.
Measures
PTSD Checklist
The PTSD Checklist (PCL; Orsillo, 2001; Weathers,
Litz,Herman, Huska, &Keane, 1993) isa self-report mea-
sure including 17 statements that each correspond to a
PTSD symptom as outlined by the DSM-IV. The measure
assesses the severity of intrusive (e.g., repeated distress-
ing memories, thoughts, or images about the potentially
traumatic event), hyperarousal (e.g., hypervigilance, diffi-
cultyconcentrating), avoidance(i.e.,efforts made to avoid
situations or thoughts associated with the potentially trau-
matic event), and emotional numbing (i.e., loss of interest
or pleasure, feelings of detachment, restricted range of af-
fect) symptoms that may occur as a result of experiencing
a stressful life event. Using a 5-point Likert scale (1 =
not at all,5=extremely), participants rate each question
according to the extent to which the symptom has both-
ered them in the past month. Strong internal consistency
has been found among a variety of populations including
VietnamandPersianGulfveterans,motorvehicleaccident
victims, and sexual assault survivors (r’s range from .94
to .97; Blanchard, Jones-Alexander, Buckley, & Forneris,
1996; Weathers et al., 1993). The PCL has been demon-
strated to have strong test–retest reliability across a 3-day
period (r=.96) as well as moderate to strong correla-
tions with other PTSD measures (Weathers et al., 1993).
A cutoff score of 50 has been used with military samples
to predict PTSD diagnoses (Weathers et al., 1993); how-
ever, Blanchard et al. (1996) found a lower cutoff score
of 44 to be associated with greater diagnostic efficiency
among a predominantly female population of trauma vic-
tims (motor vehicle accident victims and sexual assault
survivors).
Acceptance and Action Questionnaire
The Acceptance and Action Questionnaire (AAQ;
Hayes et al., 2003), is a self-report measure of expe-
riential avoidance, or the tendency of an individual to
avoid unwanted internal experiences, such as emotions,
thoughts, or bodily sensations. This study uses an earlier
16-item version of the measure, which has been found to
be highly correlated with the final 9-item version (Hayes
et al., 2003). Higher scores on the AAQ correspond to
high experiential avoidance, or the unwillingness to ex-
perience certain thoughts and feelings. Sample items in-
clude, “If I could magically remove all the painful experi-
ences I’ve had in my life, I would do so” and “Anxiety is
bad” (Hayes et al., 2003). The AAQ has adequate internal
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150 Tull and Roemer
consistency (α=.70) and has been found to be correlated
with a tendency to engage in the suppression of thoughts
in both clinical and nonclinical populations (r’s =.44 to
.50; Hayes et al., 2003). The AAQ has also been found
to be correlated with a number of measures of general
psychopathology, including measures of depression (av-
erage r=.57), anxiety (average r=.47), specific fears
(average r=.47), and trauma-related beliefs (r=.68)
andsymptoms (r=.55;Hayeset al., 2003).Providing ev-
idence for its discriminant validity, the AAQ is negatively
correlated with escape-avoidant coping (r=−.38), sug-
gestingthat the AAQ measuresageneral tendency toavoid
internal experience, regardless of the context, in contrast
to avoidance behaviors that are contextually determined
(Hayes et al., 2003).
Life Events Checklist
Participants also completed a life events checklist
(LEC; Blake et al., 1995). The checklist describes a vari-
ety of potentially traumatic events (e.g., combat exposure,
natural disasters, motor vehicle accidents, sexual assault,
etc.).Participantswere asked toindicatewhich eventsthey
had experienced, the number of times the events were ex-
perienced, and whether the events occurred during child-
hood, adulthood, or both. Of particular interest to this
study were participants’ responses to whether a sexual
assault had been experienced. On the checklist, sexual as-
sault was defined as forced, unwanted oral, anal, or vagi-
nal penetration. As assessed with the LEC, approximately
18.4% of the total sample (N=924) reported experienc-
ing a sexual assault at some point in their life. This rate is
consistentwith previous findings obtainedfrom a largena-
tionalsample ofhigher education female students (15.4%;
Koss, Gidycz, & Wisniewski, 1987) using a validated as-
sessmentof sexualassault, the SexualExperiences Survey
(SES; Koss & Gidycz, 1985; Koss & Oros, 1982).
Procedure
Students and staff from the University of
Massachusetts Boston were recruited through ques-
tionnaire distribution tables located in public areas on
the university campus. Prior to participation, participants
were informed fully, both verbally and in writing, about
the purpose of the study and potentially distressing
subject matter of the questionnaires. Students who
chose to participate in the study filled out a battery of
questionnaires that included the PCL (Weathers et al.,
1993), the AAQ (Hayes et al., 2003), and the LEC (Blake
et al., 1995). Inclusion in the present study required
endorsement of at least one sexual assault experienced in
childhood, adulthood, or both.
RESULTS
Within the current sample of female sexual assault
survivors, 34.9% of the sample met or exceeded the cutoff
score of 44 on the PCL, thereby suggesting that these
individuals may experience trauma-related symptoms to
such severity that a diagnosis of PTSD is warranted.
As assessed by the PCL, all of the PTSD symptoms
(avoidance, intrusion, hyperarousal, and emotional numb-
ing)were significantlyand positively correlated. Allof the
PTSD symptoms were significantly and positively associ-
ated with experiential avoidance, as assessed by the AAQ
(see Table I).
In order to determine whether a relationship between
hyperarousal and emotional numbing symptoms existed
among female sexual assault survivors similar to that pre-
viously found among combat veterans (see Flack et al.,
2000; Litz et al., 1997), a hierarchical regression analysis
wasperformed. Severityofemotional numbing symptoms
was the dependent variable while the other PTSD symp-
tom clusters served as the predictor variables. The predic-
tor variables entered in the first step of the equation were
severity of intrusion and avoidance symptoms. Similar to
analysesperformed by Litzet al. (1997),severityof hyper-
arousalsymptoms was enteredinthe final stepso as topro-
videthe mostconservativetest of the relationship between
emotional numbing and hyperarousal symptoms. Results
demonstrate that severity of hyperarousal symptoms sig-
nificantlypredicted emotionalnumbing above and beyond
the avoidance and intrusion symptoms of PTSD (β=.41,
p<.001; see Table II), accounting for an additional 10%
of the variance in the severity of emotional numbing
symptoms. Intrusion, though not avoidance, symptoms
were also found to be a significant predictor of emotional
Table I. Correlations Between PTSD Symptoms and Experiential
Avoidance
Experiential
Variable Avoidance Intrusion Hyperarousal EN avoidance
Avoidance 1.00
Intrusion .72∗1.00
Hyperarousal .60∗.57∗1.00
EN .53∗.61∗.63∗1.00
Experiential .42∗.40∗.42∗.37∗1.00
avoidance
∗p<.01.
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Alternative Explanations of Emotional Numbing 151
Table II. Hierarchical Regression Analysis Predicting Emotional
Numbing With Avoidance, Intrusion, and Hyperarousal Symptoms
Step and predictor variables Adj. R21R2β(final step)
Step 1 .38 .39∗
Avoidance .01
Intrusion .37∗
Step 2 .48 .10∗
Hyperarousal .41∗
∗p<.001.
numbing in the final model (β=.37, p<.001). Given
this finding, an additional hierarchical regression analy-
sis was performed where severity of hyperarousal symp-
toms was entered in the first step followed by the avoid-
ance and intrusion symptom severity scores in the second
step. Severity of emotional numbing symptoms was again
the dependent variable. This analysis served to further
test the strength of the relationship between hyperarousal
and emotional numbing symptoms by examining whether
symptoms of avoidance and intrusion make a significant
contributiontothe prediction ofemotional numbing above
and beyond that of hyperarousal. Symptoms of avoidance
and intrusion significantly improved the model above and
beyond severity of hyperarousal symptoms (1R2=.09,
p<.001) though this was largely due to the fact that
severity of intrusion, not avoidance, symptoms was found
to be a highly significant predictor of emotional numb-
ing symptoms in the final model (β=.37, p<.001; see
Table III). Severity of hyperarousal symptoms also re-
mained a significant predictor of emotional numbing in
the final model (β=.41, p<.001).
To examine if the demonstrated relationship between
hyperarousal and emotional numbing symptoms was a
result of hyperarousal serving as a proxy risk factor in
the relationship between experiential avoidance and emo-
tional numbing, participants’ scores on the AAQ were in-
troduced in the second step of the regression equation
Table III. Hierarchical Regression Analysis Predicting Emotional
Numbing With Hyperarousal Symptoms Entered First Followed by
Avoidance and Intrusion Symptoms
Step and predictor variables Adj. R21R2β(final step)
Step 1 .39 .39∗
Hyperarousal .41∗
Step 2 .48 .09∗
Avoidance .01
Intrusion .37∗
∗p<.001.
Table IV. Hierarchical Regression Analysis Predicting Emotional
Numbing With Avoidance, Intrusion, and Hyperarousal Symptoms and
Experiential Avoidance
Step and predictor variables Adj. R21R2β(final step)
Step 1 .37 .38∗∗
Avoidance −.02
Intrusion .35∗∗
Step 2 .39 .02∗
Experiential avoidance .07
Step 3 .48 .10∗∗
Hyperarousal .42∗∗
∗p<.05.∗∗p<.001.
(i.e., after the intrusion and avoidance symptoms). As be-
fore, severity of hyperarousal symptoms was entered in
the final (third) step. If the relationship between hyper-
arousaland emotionalnumbing symptomswas merelythe
result of the relationship of each of these to experiential
avoidance, hyperarousal symptoms would not continue
to predict emotional numbing symptoms (or the rela-
tionship would weaken) when controlling for experien-
tial avoidance. Results indicate that, without the inclusion
of hyperarousal symptoms, experiential avoidance signif-
icantly predicted emotional numbing above and beyond
the avoidance and intrusion symptoms of PTSD (β=.14,
p<.05), accounting for an additional 2% of the variance
in the severity of emotional numbing symptoms. When
severity of hyperarousal symptoms was entered into the
model in the third and final step of the regression equa-
tion, experiential avoidance no longer remained a signifi-
cant predictor of emotional numbing. Instead, the severity
of hyperarousal symptoms once again significantly pre-
dicted emotional numbing symptoms above and beyond
theavoidanceand intrusionsymptoms of PTSD,as wellas
experiential avoidance (β=.42, p<.001; see Table IV),
again accounting for an additional 10% of the variance in
the severity of emotional numbing symptoms. As before,
intrusion, but not avoidance, symptoms remained a signif-
icant predictor of emotional numbing in the final model
(β=.35, p<.001).
DISCUSSION
Using a sample of female sexual assault survivors,
this study extended Litz and colleagues’ previous findings
(Litz et al., 1997) obtained from a sample of Vietnam
combat veterans. Symptoms of hyperarousal significantly
predictedemotionalnumbing above and beyondtheavoid-
ance and intrusion symptoms of PTSD. Results further
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152 Tull and Roemer
demonstrated that hyperarousal symptoms remained a
significant predictor of emotional numbing when con-
trolling for the relationship between emotional numbing
and experiential avoidance, suggesting that experiential
avoidance is not a major risk factor for the development of
emotional numbing symptoms with hyperarousal serving
only as a proxy risk factor due to its association with
experiential avoidance. In other words, the relationship
between hyperarousal and emotional numbing symptoms
is not the result of the relationship of each of these
to experiential avoidance. The present study does not
provide support for an alternative explanation of the pro-
posed and previously demonstrated relationship between
hyperarousal and emotional numbing symptoms. Despite
this, it warrants mention that experiential avoidance was
found to explain a significant (albeit minimal) percentage
of the variance in emotional numbing symptoms above
and beyond the intrusion and avoidance symptoms of
PTSD (although it did not remain a significant predic-
tor upon inclusion of hyperarousal symptoms in the
model).
Despite consistency with previous findings, several
limitations need to be taken into consideration when in-
terpreting results. Information pertaining to participants’
sexual assault histories, PTSD symptoms, and experien-
tial avoidance was obtained through self-report data. In-
dividuals who have encountered a potentially traumatic
event may experience difficulty, or even unwillingness, in
openly expressing their thoughts and feelings about that
event through self-report. A tendency to engage in expe-
riential avoidance may also interfere with awareness of
internal experiences and, subsequently, accurate report-
ing of these experiences. However, it appears as though
the use of self-report data was not associated with any
more limitations than those present in interview data, es-
pecially given that results were consistent with previous
studies using interview data to examine the relationship
between hyperarousal and emotional numbing symptoms
(e.g., Flack et al., 2000; Litz et al., 1997).
Even though all of the participants reported experi-
encing a sexual assault, they were not required to respond
to the PCL for symptoms specifically related to their sex-
ual assault. The PCL asks participants to rate the extent to
which they experience a variety of symptoms associated
with PTSD but does not require participants to specify the
traumatic event to which those symptoms are related. Par-
ticipantsin this studymayhavebeen describingsymptoms
associated with another traumatic event. This is possible
given that the majority of the participants in the current
sample reported at least one other stressful experience on
the LEC. For example, 4.1% reported past combat expo-
sure, 67.1% reported experiencing a physical assault at
some point in their life, and 22.9% reported experiencing
an assault involving a weapon (although it is important to
keepinmind that thelattertwomay have been experienced
concurrent with the sexual assault). Even though the re-
sultswould still providesupportfor the previouslydemon-
strated relationship between hyperarousal and emotional
numbingsymptoms, the relationship may not be exclusive
to the experience of sexual assault, but instead, to a wide
variety of traumatic events.
Results indicated that 34.9% of the present sam-
ple experienced PTSD-related symptoms to such sever-
ity that a diagnosis of PTSD may be warranted, as based
upon the cutoff score proposed for nonmilitary popula-
tionson thePCL. While this percentage issimilar toprevi-
ously reported rates from the National Comorbidity Study
(45.9% of women who reported rape as their most upset-
ting trauma developed PTSD; Kessler, Sonnega, Bromet,
Hughes, & Nelson, 1995), it is important to note that the
PCL is a self-report measure of symptom severity only
and therefore, cannot be used to diagnose PTSD. How-
ever, this finding does speak to the extent of symptom
severity experienced by the present sample.
Another limitation concerns the measure of expe-
riential avoidance, the AAQ. Given theoretical support
for the role of experiential avoidance in the development
and maintenance of a variety of psychological disorders
(see Hayes et al., 1996) and its theoretical relevance to
the development and maintenance of PTSD in particu-
lar, it seemed important to explore the role of experien-
tial avoidance in the relationship between hyperarousal
and emotional numbing symptoms. However, though ex-
periential avoidance is receiving increasing attention as a
construct of empirical interest, it is still a relatively new
construct, and therefore, the only measure developed thus
far to assess it, the AAQ, is not yet published. Preliminary
data (Hayes et al., 2003) nonetheless support its validity,
suggesting it is an adequate measure of an individual’s
tendency to avoid emotional experiences.
Individuals suffering from PTSD may not always
be in an emotionally numb or unresponsive state. Litz
(1992) has suggested that deficits in emotional processing
(or emotional numbing) occur as a result of episodes of
hyperemotionality associated with exposure to a trauma
cue. This study assessed trait rather than state levels of
these symptoms and thus may have obscured important
relationships between state occurrences of hyperarousal,
emotional numbing, and experiential avoidance. Experi-
mental studies where hyperarousal, emotional numbing,
and experiential avoidance are assessed after the presenta-
tion of a trauma-related cue would aid in determining the
exact nature of the relationship between these phenomena
in a trauma-cued state.
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Alternative Explanations of Emotional Numbing 153
Similar to previous studies, the correlational and
cross-sectional nature of the data prohibits stating with
certainty the actual direction of the relationship between
hyperarousal and emotional numbing symptoms. Experi-
mentalstudies where hyperarousalisactivelymanipulated
in the lab would further elucidate the role of hyperarousal
symptoms in the development and maintenance of emo-
tional numbing symptoms in PTSD. Longitudinal studies
would also aid in determining the developmental course
of trauma symptoms and their interrelationships.
Despite these limitations, the findings from the
presentstudy suggestthathigh levelsofarousal may result
in the depletion of emotional resources, thereby leading
toemotional numbing,consistent withLitz (1992).Symp-
toms of intrusion were also found to be a significant pre-
dictor of emotional numbing symptoms suggesting that
their role in the development and maintenance of emo-
tional numbing symptoms warrants further investigation.
Although the present study does not provide support for
the exclusive role of experiential avoidance in emotional
numbing, it would be premature to rule out the impor-
tance of the intentional avoidance of emotional experi-
ence in emotional numbing symptoms, as well as PTSD
in general. The intentional suppression or avoidance of
distressing thoughts or emotions may become automatic
over time, such that individuals may not be able to accu-
rately report the extent of their engagement in these strate-
gies.Experimentalstudies in which suppressionisactively
manipulated may shed further light on the role of emo-
tional suppression or avoidance in the development and
maintenance of emotional numbing symptoms. Experien-
tial avoidance also demonstrated modest correlations with
all PTSD symptom clusters suggesting that a tendency to
avoid internal experience may be related to all aspects of
PTSD. Consequently, further research on the relationship
between experiential avoidance and all PTSD symptoms
(for example, intrusions, given evidence from the thought
suppression literature that intrusions may occur as a result
of suppression attempts) is warranted. Experiential avoid-
ance is a broad term encompassing avoidance of a vari-
ety of internal experiences (e.g., emotions, thoughts, and
bodilysensations), andfuture studies may benefit fromfo-
cusing on more specific aspects of experiential avoidance
and their possible influence on the relationship between
hyperarousal and emotional numbing symptoms.
ACKNOWLEDGMENTS
This research was supported in part by National In-
stitute of Mental Health grant MH-59044 and an inter-
nal grant from the University of Massachusetts Boston
(both to the last author). Portions of this study were pre-
sented at the 35th Annual Convention of the Association
for Advancement of Behavior Therapy in Philadelphia,
PA (2001). We thank Sue Orsillo, Amy Wagner, and Kim
Gratz for their valuable suggestions in the preparation of
this manuscript.
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