PERSONALITY
10.1177/0146167204271419
Aron
et al. / SENSITIVITY
AND SOCIALANDPSYCHOLOGYSHYNESS
BULLETIN

Adult Shyness:
The Interaction of Temperamental Sensitivity
and an Adverse Childhood Environment
Elaine N. Aron
Arthur Aron
Kristin M. Davies
State University of New York at Stony Brook
This article examines the relation between adult shyness andsensory-processing sensitivity and posits a new model in which
the interaction of sensitivity and adverse childhood environment
leads to negative affectivity (with the highly sensitive being more
impacted), which in turn leads to shyness. Consistent with thismodel, two questionnaire studies (Ns = 96 and 213) supported
three hypotheses: (a) sensory-processing sensitivity interacts withrecalled quality of childhood parental environment to predictshyness, (b) sensory-processing sensitivity interacts in the same
way with childhood environment to predict negative affectivity,and (c) the interaction effect on negative affectivity mediates theeffect on shyness. Hypothesis 2 was tested and supported in an
additional questionnaire study (N = 393) and also in an experiment (N = 160) that manipulated negative contemporaneous
experience as an analog for adverse childhood environment.

model: an interaction between sensory-processing sensitivity and adverse childhood environment leads tonegative affectivity, which in turn leads to shyness.
SENSORY-PROCESSING SENSITIVITY

Aron (1996, 1999; Aron & Aron, 1997) describedsensory-processing sensitivity as an individual difference
characteristic in which those who are high are particularly sensitive to subtle stimuli, easily overstimulated,
prone to “pause to check” in a novel situation, and preferto reflect and revise their cognitive maps after an experience. Aron and Aron (1997) developed a measure of thetrait that is unifactorial, reliable, and with substantial
convergent and discriminant validity. The trait is meant
to encompass what other adult personality researchers
have variously described as a weak nervous system (Pavlov, 1927), low screening (Mehrabian, 1976, 1991), augmenting (of stimulation; Petrie, 1967), reducing (ofevoked potential; Buchsbaum, Haier, & Johnson, 1983),
reactivity (Strelau, 1983), avoidance temperament(Elliot & Thrash, 2002), and nondisinhibition or reflectivity (Patterson & Newman, 1993). In addition, it may berelated to arousal focus (Feldman, 1995), which ishypothesized to involve individual differences in attention and processing of somatic states. Sensoryprocessing sensitivity is also meant to encompass,roughly, what child temperament researchers have

Keywords: shyness; neuroticism; childhood; sensitivity; depression;anxiety; temperament

A series of previous studies (Aron & Aron, 1997) sup-ports the hypothesis that sensory-processing sensitivity is
an individual difference characteristic in adults that is
at least partially independent of social introversion andnegative affectivity (fearfulness, anxiety, depression). As
discussed below, this hypothesized temperament trait
approximately corresponds to the physiological aspectof what has often been labeled introversion, as well as totemperament traits that carry a variety of names, including inhibitedness and reactivity. This article extends thatwork to the relation of sensory-processing sensitivity toadult shyness. We propose that these two seemingly related constructs of sensitivity and shyness are separable
but are linked through a relatively simple hypothesized

Authors’ Note: Please address correspondence to Elaine N. Aron, State
University of New York at Stony Brook, Psychology Department, Stony
Brook, NY 11794-2500; e-mail: elainearon@hotmail.com.
PSPB, Vol. 31 No. 2, February 2005 181-197
DOI: 10.1177/0146167204271419© 2005 by the Society for Personality and Social Psychology, Inc.

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called inhibitedness (Kagan, 1994), infant or innate shyness (Cheek & Buss, 1981; Daniels & Plomin, 1985),
reactivity (Rothbart, 1989; Strelau, 1983), and thresholdof responsiveness (Thomas & Chess, 1977).1
Above all, Aron and Aron (1997) note that the trait isprobably the same as the aspect of introversion that
Eysenck (1991), Stelmack (1990), Stelmack and Geen
(1992), and others suggest accounts for the large physiological differences between extroverts and introverts,
such as faster auditory brainstem evoked potentials (DePascalis, 1993), greater sensitivity in signal detection
tasks (Harkins & Geen, 1975), and lower pain thresholds(Barnes, 1975). “Overall there is a good deal of evidence
that introverts are more sensitive to physical stimulation
than extraverts” (Stelmack & Geen, 1992, p. 227). However, in a series of seven studies with diverse samples
using a variety of measures and analysis strategies, Aronand Aron (1997) found this aspect of introversion to be
separable from the larger concept of introversion as it istypically measured (which includes sociability). For
example, correlations between sensitivity and standard
measures of introversion are clearly less than unity(ranging from .12 to .52) and have predictably different
patterns of correlations with other variables when each ispartialed from the other.
Whatever name is assigned to this individual difference, it seems likely that it is an inherited temperament
trait given the extensive data on that point from Eysenck(1981), Daniels and Plomin (1985, who used a full adoption design), Kagan (1994), and many others. Indeed, avery similar genetic trait is found in a wide variety of animal species (for a review, see Aron & Aron, 1997). One
suggested explanation (Wilson, Coleman, Clark, &Biederman, 1993) is that there are two behavior styles
because there are two survival strategies—processing
information thoroughly before acting (“do it once anddo it right”) versus acting immediately (“go for it”). Nevertheless, the model we propose is entirely consistent
with the possibility that the trait is not inherited but
simply appears early.
Finally, this characteristic seems best represented as adichotomous variable (rather than a continuum) with
10% to 35% highly sensitive, given the infant observation data (e.g., Kagan, 1994), formal taxometric work
(Woodward, Lenzenweber, Kagan, Snidman, & Arcus,
2000), and the extensive animal literature cited above
where it is almost always observed as a dichotomous variable in these proportions. (For a discussion of typological conceptions of personality, see Robins, John, &Caspi, 1998; for a discussion of the related idea of global
traits, see Funder, 1991.) Indeed, for Drosophilia, a single gene has been identified distinguishing “sitters”
from “rovers” (sitters evidence greater neuron excitability, synaptic transmission, and nerve connectivity, consis-

tent with sitters using a strategy of greater information
processing; Renger, Yao, Sokolowski, & Wu, 1999).
Finally, samples of adults administered our sensitivity
measure have consistently yielded bimodal distributions
and the sensitive and nonsensitive individuals fall into
distinct clusters when measured on a number of variables (Aron & Aron, 1997).
NEGATIVE AFFECTIVITY ARISING FROM THE INTERACTION
OF SENSITIVITY AND CHILDHOOD ENVIRONMENT

We begin with the proposed relation of sensitivity tonegative affect in general before turning to the proposed further-downstream relation to shyness.2 If those
who are high on sensory-processing sensitivity process all
experiences more thoroughly, including social and emotional experiences, these individuals also would havebeen especially affected by their childhood environment. Aron and Aron (1997) found results consistent
with this view in cluster analyses of three independent
samples (including a random-digit-dialing telephonesurvey). In each sample, there appeared to be two distinct clusters of highly sensitive individuals (along with athird, much larger cluster who were not highly sensitive). The smaller of the two highly sensitive clusters ineach sample, about a third of the highly sensitive individuals, reported less happy childhoods and more negative
affectivity; the larger of the two highly sensitive clusters
in each sample were just as sensitive but reported childhoods and negative affectivity at about the same level as
the not highly sensitive cluster. Furthermore, in anotheranalysis of these samples, among those who reported relatively objective problems in their childhood home suchas alcoholism or mental illness, those who were highly
sensitive were more likely than those not highly sensitive
to have reported difficult childhoods. These various
results suggested the possibility of a general pattern of
an interaction between temperamental sensitivity and ahistory of many stressors that leads to chronic negative
affect.
Some researchers working with children have reported such an interaction looking at temperamental
qualities similar to sensitivity (or perhaps sensitivity thathas been differently labeled—see earlier discussion andNote 1). In a longitudinal study, Hagekill (1996)
reported that the most variance in children’s neuroticism was accounted for by an interaction of “low sociability” as an infant temperament trait and negative life
events, such that children evidencing initial low sociability and having more negative life events were more fearful at later ages. Fox (1996) found that infants evidencing more of a temperament trait of “negative affectivity”(sensitive infants’ reaction to levels of test stimulationthat would be comfortable to nonsensitive infants?) andAron et al. / SENSITIVITY AND SHYNESS
right hemisphere activity had more variable outcomes at
4. Medical researchers Boice et al. (1995) studied highand low reactive children (measured as change frombaseline of heart rate and immune reactivity in a challenge situation). High reactive children in stressful
home and school conditions were more prone to illness
and injury (likely signs of negative affect) than nonreactive children. However, when in normal-stress environments, high reactive children were less prone to illness and injury than nonreactive children. Gannon,
Banks, and Shelton (1989) found similar results for adolescents (according to their tables—they only discussed
the increased illness and injuries under high stress). In
sum, as Boice et al. (1995) speculated, “Children with aheightened sensitivity to psychosocial processes [might
have superior health] under low-stress, nurturing, andpredictable conditions, in which social cues denote encouragement and acceptance” (p. 419) because of“a heightened sensitivity to the character of the socialworld” (p. 420).
Gunnar, Nachmias, and their colleagues (Gunnar,
1994; Nachmias, Gunnar, Mangelsdorf, Hornik Parritz,& Buss, 1996) report similar interactions with regard to“inhibited” children. These researchers employed laboratory experiments with novel, arousing situations tocompare inhibited and uninhibited children with orwithout secure attachments to their mothers. Inhibitedchildren in general (i.e., regardless of their security of
attachment) entered the novel situations gradually andevidenced adrenaline reactions. However, only thoseinhibited children with insecure attachments showed arise in cortisol. (Security of attachment style was not
related to cortisol levels in noninhibited children.)
Chronically high cortisol levels would certainly contribute to the development of negative affectivity. For example, cortisol disturbs sleep, and sleep disturbance leads
to still greater vulnerability to negative affect, especiallyin children (Weissbluth, 1989). Consistent with ourinterpretations, Stansbury (1999) concluded from his
own review of these studies that there are two pathways toadult hyperreactivity of the adrenocortical system (signsof anxiety and depression)—temperament and less than
optimal mothering early in life. But the majority of variance “would be captured by studies of the interactions
between these two variables during early development”(p. 41).
SHYNESS

Shyness—the fear of negative social evaluations that
leads to discomfort and limitations on the desire forsocial contact—has richly deserved increasing focus. At
least 40% to 50% of Americans label themselves as
dispositionally shy, 75% of whom report they do not like183

being shy and 66% of whom find it a personal problem(for reviews, see Carducci & Zimbardo, 1997; Cheek &Krasnoperova, 1999). Beginning with Baldwin (1894), it
has been observed that shyness sometimes appears early,
as if inherited, and sometimes appears later, as if
learned. Studies of shyness have consistently shown thatthe family environment (e.g., Daniels & Plomin, 1985;
see Eastburg & Johnson, 1990, for a review) and experiences with peers (e.g., Roopnarine, 1985) can be asimportant as genetics. Nevertheless, the high heritabilityof shyness (Daniels & Plomin, 1985) suggests some
genetic factor is involved, although not necessarily a“shyness gene.”
Our suggestion is that something basic like sensoryprocessing sensitivity is probably the aspect that is inherited but does not become shyness except in the context
of a problematic environment, particularly in childhoodor adolescence. When observing infants, a preference topause to check and a withdrawal from overstimulation
may be understandably construed as shyness, and as children develop self-consciousness and choice, this temperament quality may well manifest as preferring less stimulating environments, such as preferring to spend timewith familiars. But these behaviors are not yet shyness. As
Nachmias et al.’s (1996) data suggested, when “inhibited” toddlers are placed in a novel situation, they pause
to observe and evidence increased adrenaline, an inhibition only in the sense of initial reaction. Environmental
stressors seem to be required to turn this temperamentquality, a high attention to novelty, into chronic fear ofnovelty and later into fear of social evaluation. In the
Nachmias et al. work, the stressor was an insecure attachment style (in particular, anxious and intrusive
involvement by the mothers of the insecure “inhibited”
toddlers).3
That shyness or social withdrawal is the result of aninteraction of some aspect of temperament and environment is consistent with the literature on children. For
example, Rubin and his colleagues (e.g., Mills & Rubin,
1993; Rubin, LeMare, & Lollis, 1990) have been
researching a model in which social withdrawal in children is the result of an interaction of unnamed inborn
characteristics, socialization within and outside of thefamily, and the parents themselves—such as their inability to respond appropriately to this temperament difference because of their attitudes and beliefs, with negative
effects increasing when the family is under stress. Likewise, Engfer (1993) found that “children who as infants
were already somewhat more sensitive and vulnerable
showed a marked increase in shyness under the cumulative impact of deteriorating family relationships and an
abrupt change in the peer-group environment” (p. 77;
i.e., changing schools or school classrooms). However,this interaction has not been studied in adults. Further-

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more, the question remains as to the underlying natureof the temperament trait that interacts with life history tocreate shyness.
Of course, negative affect and shyness can develop ina not highly sensitive person as well through repeatedexperiences of criticism and rejection in childhood oreven adulthood. What we hypothesize is that highly sensitive individuals develop these more readily because
they experience the same adverse environment morenegatively. (There are also, no doubt, ways shyness candevelop independently of negative affectivity, such as
through direct modeling.) Furthermore, because highsensitivity involves processing experiences more thoroughly, it seems likely that, for sensitive individuals, distressing experiences would lead to more distressed, negative affect (anxiety and depression) and many such
experiences would lead to chronic negative affect. If
these (or any) individuals enter a social situation alreadyfeeling or anticipating negative affect, it seems more
likely that these distressed individuals would seek inmemory other negative moments. In social situations,these would be other moments of being negatively evaluated, which they would now fear again. Thus, in addition
to hypothesizing sensitivity-childhood interaction’s
impact on both negative affectivity and shyness, we also
hypothesized that the impact on negative affectivity is amediator of the effect on shyness. (For direct evidence ofthe relation of negative affectivity to social behavior, see
Furr & Funder, 1998.)

Figure 1 (a) The overall hypothesized model. (b) Predicted relationof childhood parental environment to negative affectivity
and shyness for highly sensitive individuals. (c) Predicted
relation of childhood environment to negative affectivity
and shyness for not highly sensitive individuals.

SUMMARY OF OUR MODEL AND HYPOTHESESTHE PRESENT RESEARCH

Our overall model is shown in Figure 1a. As shown in
Figure 1b and 1c, the predicted pattern is that the pathfrom childhood environment to negative affectivity isstronger for individuals who are highly sensitive than for
those who are not highly sensitive and that this negative
affectivity in turn is a cause of increased shyness.This
model implies three hypotheses:

As a first test of central aspects of our hypothesizedmodel, we conducted four studies. Each study employed
our measure of sensory-processing sensitivity (Aron &Aron, 1997) and measures of negative affectivity. The
first two studies, which focused on the entire model, also
included Cheek’s (1983) shyness measure and retrospective measures of the quality of the parental environment during childhood. (We chose to ask questions
about parents because they are probably the largest
potentially negative environmental influence but do notmean to suggest that parents are the only influence.)
Study 1 used the same brief parental environment andnegative affectivity measures originally constructed aspart of the Aron and Aron (1997) research. Study 2 was a
replication of Study 1 with a larger sample, using a procedure in which different questionnaires appeared as separate studies and employing measures of parental environment and negative affectivity with established strong
psychometric properties and evidence of validity. Study 3
was a further replication, with a new large sample, of the
aspect of our model regarding the hypothesized interaction of sensitivity and childhood environment pre-Hypothesis 1: There should be an interaction of sensoryprocessing sensitivity and childhood environment inpredicting shyness, such that highly sensitive individuals, compared to not highly sensitive individuals,
should demonstrate a stronger association between adverse childhood environment and shyness.
Hypothesis 2: There should be an interaction of sensoryprocessing sensitivity and childhood environment inpredicting negative affectivity, such that highly sensitive
individuals, compared to not highly sensitive individuals, should demonstrate a stronger association between
adverse childhood environment and negative affectivity.
Hypothesis 3: Negative affectivity should mediate the relation between shyness and the interaction of sensoryprocessing sensitivity and childhood environment.

Aron et al. / SENSITIVITY AND SHYNESS
dicting negative affectivity, employing the same Study 1
negative affectivity measure in addition to a different
combination of childhood environment measures.
Study 4 was an experiment testing the underlying principle that negative experiences create greater negative
affect in highly sensitive individuals.
We are aware of the limitations of asking adults torecall conditions from their childhood (e.g., Cutler,
Larsen, & Bunce, 1996; Larsen, 1992). However, thelikely recall biases (individuals who are sensitive or withnegative affectivity or shyness recalling more negative
childhoods) would lead to effects opposite to those predicted by our model. For example, consider two individuals with equal levels of negative affectivity or shyness but
one is highly sensitive and the other is not. Any bias fromnegative affectivity or shyness will be the same for bothindividuals. But if there is also a negative bias effect ofsensitivity, the highly sensitive individual should report aworse childhood than the not highly sensitive individual.
However, our model predicts that the not highly sensitive individual will report a worse childhood than thehighly sensitive individual. This is because our model
hypothesizes that it takes a worse childhood to impact a
not sensitive individual to the same degree as a sensitive
individual. That is, if the highly sensitive individual ismore affected than the not highly sensitive individual byhis or her childhood environment, then to end up withan equal level of negative affectivity or shyness, thehighly sensitive person would need a less adverse childhood. (We return to this point again in the General Discussion; see also Figure 11.)
There are four additional reasons the recall bias concerns are somewhat minimized here. First, a negative
recall bias for sensitivity would predict a correlation
between sensitivity and reported adverse childhood
environment. However, as will be seen, across the threestudies involving childhood environment, the correlations with sensitivity were small and averaged near zero(–.03). Second, the specific measures of adverse childhood events in Studies 1 and 2 included scales focusedon relatively objective childhood events, and the otherkey childhood measure in Studies 2 and 3 has beenfound to correlate strongly with objective childhood
events in other research (Parker, 1986). Third, in Study4, we experimentally manipulated current negative experience rather than relying on retrospective self-reportat all. Fourth, we believe that the novelty and broad significance of the present model in the context of childhood environment are such that even a less than optimal
test suggests important new thinking about the role ofchildhood environment and temperament in relation toadult negative affectivity and shyness.
A more general concern of relying so strongly on selfreport measures of any kind is the possibility of everything-185

is-correlated-with-everything kinds of interpretations
due to common method variance, such as possible general response biases. However, in these studies, all predicted effects are tested in analyses in which other selfreport variables (with likely similar method variance andbiases) are partialed out. That is, any common method
variance and general response biases among focal measures are removed from the tests of the hypothesized
relationships.
Finally, there is the issue of the specificity of sensoryprocessing sensitivity in relation to other possible
variables that may covary with it, such as social introversion and negative affectivity. As noted, we conceptualize
sensory-processing sensitivity as roughly the same as anumber of variables that have been studied under othernames, such as reactivity and inhibitedness. Thus, we do
not attempt to distinguish sensitivity from these variables
but rather intend that our results should generalize tothem. As also noted earlier, Aron and Aron (1997) foundin a series of seven studies with different samples andmethods that sensory-processing sensitivity is at least partially independent of social introversion and negative
affectivity. Still, it remains possible that the specificeffects found here arise from overlap that remains withthese other variables. Fortunately, we were able to examine effects controlling for a measure of social introversion in Studies 1, 2, and 4. Also, throughout, mostanalyses either controlled for direct effects of negative
affectivity or it is a dependent measure in analyses inwhich direct sensitivity effects are held constant (so thatany overlap with sensitivity and negative affectivity isremoved from the focal analyses). Furthermore, if negative affectivity or shyness represent a common underlying construct with sensitivity, this would imply main
effects of both negative affectivity or shyness and sensitivity but would not imply our hypothesized interactions.
(We return to this issue in the General Discussion; seealso Figure 10.)STUDY 1

MethodParticipants were 96 1st- and 2nd-year State Universityof New York at Stony Brook psychology undergraduates(47 women, 46 men, 3 who did not indicate gender; M
age = 18.7; in all studies, the few participants 25 or older
were excluded from analyses).
Sensory-processing sensitivity was measured using theHighly Sensitive Person Scale (Aron & Aron, 1997), a 27item questionnaire that has shown a unifactorial structure, solid reliability, and discriminant and convergent
validity (example items include, “Are you made uncomfortable by loud noises?” and “Are you particularly sensi-

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tive to the effects of caffeine?”). In this study, alpha = .85.
As noted earlier, sensory-processing sensitivity appears
to be a dichotomous variable with about 10% to 35%
highly sensitive (and we have found the proportion
tends toward the high end among psychology students).
Thus, following procedures used in previous research,
we inspected the distribution for an appropriate cutoff
in which 20% to 35% would be in the highly sensitive
group. This yielded a dichotomous variable with 35 classified as highly sensitive and 61 not. All analyses employed this dichotomous variable. (We also conducted
all analyses here treating sensitivity scores as a continuous variable. In every case, the results were in the same
direction and had at least the same level of significance.
However, we report results using the dichotomy becauseof theory and evidence reviewed earlier suggesting thatthe underlying construct is dichotomous.)
Shyness was measured using Cheek’s (1983) Revised
Cheek and Buss Shyness Scale, a 13-item questionnaire with demonstrated strong validity and reliability(example items include, “I feel tense when I’m with people I don’t know well” and “I am socially somewhat awkward”). Alpha in this study was .90.
Childhood parental environment was assessed withthe six-item measure Aron and Aron (1997) used (example items include, “Was mental illness a problem in yourimmediate family while you were growing up?” and “Wasalcoholism a problem in your immediate family while
you were growing up?”).4 Alpha here was a marginallyadequate .63. (However, alpha is not entirely appropriate because some items are causes rather than indicatorsof the construct; see Bollen & Lennox, 1991. Indeed,breadth of coverage seems more important here thaninternal consistency. Also, any lack of reliability works
against our hypotheses.) Note that the items in this measure emphasize relatively objective conditions, reducing
opportunities for recall bias.
Negative affectivity was assessed with the three-item
measure Aron and Aron (1997) used: “Are you a tense or
worried person by nature?” “Are you prone to fears?”and “Are you prone to depression?” Alpha in this study
was .75.
Finally, our questionnaire included two items onsocial introversion: “Do you prefer to go out with one or
two friends (vs. a larger group)?” and “Do you like having
just a few close friends (as opposed to a large circle offriends)?” (alpha = .70). Aron and Aron (1997) foundthis two-item scale correlated highly with standard measures of social introversion.
Results
As shown in Table 1, correlations were all substantiallyand significantly less than 1.5 Gender did not significantly moderate any of the correlations or hypothesis

TABLE 1: Correlations Among Key Variables in Studies 1 and 2

1. Sensitivity
2. Adverse parental environment
3. Negative affectivity
4. Shyness

1

2

3

4

—
–.03
.47**
.26**

.16*
—
.20*
.03

.40**
.33**
—
.51**

.20**
.22**
.51**
—

NOTE: Correlations below the diagonal are for Study 1 (N = 96); correlations above the diagonal are for Study 2 (N = 213). Based on 1%
confidence intervals, all correlations are significantly less than 1 (seeNote 5).
*p ≤ .05. **p ≤ .01.

tests in any of the four studies (with one exception in
Study 2).
Hypothesis 1. The predicted interaction was significant, t(91) = 1.79, p < .05. (Throughout, tests of hypothesized effects are one-tailed.) This interaction (and allinteractions in the article other than in the Notes) wastested in the standard fashion (Aiken & West, 1991)
using a regression model in which the predictors were
the two variables hypothesized to interact (sensitivity, as
a dummy-coded variable; childhood environment, as acentered continuous variable) and a term representing
the product of the two; the crucial test is the t value of the
product term in the context of this overall equation.6 As
predicted, for highly sensitive individuals, the worse thechildhood environment, the greater the shyness (r =.28); however, for the not highly sensitive individuals,
this link was near zero (r = –.09).(see Figure 2).
Hypothesis 2. This predicted interaction approachedsignificance, t(91) = 1.50, p = .07.7 For highly sensitive
individuals, the worse the parental environment, thegreater the negative affectivity (r = .40); however, for nothighly sensitive individuals, this link was much smaller(r = .12) (see Figure 3).
Hypothesis 3. The results met all four of Baron and
Kenney’s (1986) conditions for the predicted mediation. As shown in Figure 4, (a) the unmediated pathfrom the distal cause (Childhood Environment X Sensitivity term residual after removing the effects of eachmain effect) to the distal effect (shyness) was significant(beta = .68, p < .05, per the Hypothesis 1 result); (b) the
path from the distal cause to the mediator (negative
affectivity) approached significance (beta = .51, p = .07,
per the Hypothesis 2 result); (c) the path from the mediator to the distal effect, when controlling for the distal
cause, was significant (beta = .50, p < .01); and (d) the
unmediated relation of the distal cause to the distal effect (beta = .68) was reduced to nonsignificance (beta =.43) when the mediator was included in the model. The
direct test of the mediation (Sobel’s test) approachedsignificance, Z = 1.46, p = .07 (see Note 7).

Aron et al. / SENSITIVITY AND SHYNESSFigure 2 Relation of adverse childhood parental environment toshyness for highly sensitive and not highly sensitive
individuals.
NOTE: Difference in slopes, t(91) = 1.79, p < .05 (Study 1, test of Hypothesis 1).

187

Figure 4 Standardized path coefficients for predicting shyness frominteraction of sensitivity and adverse childhood parental
environment, unmediated (top model) and mediated bynegative affectivity (bottom model).
NOTE: In both models, sensitivity and poor parental environment arealso included individually as exogenous variables with effects on the interaction term but are not shown. Mediation (Sobel’s test) Z = 1.46, p =.07 (Study 1, test of Hypothesis 3).
†p < .10. *p < .05. **p < .01.

Specificity of sensory-processing sensitivity. In each analysis
reported above, the pattern and significance levelremained the same when the social introversion measure was included in the equation. As noted in the Introduction, the specificity of sensory-processing sensitivity
or shyness in relation to negative affectivity is not muchat issue here because negative affectivity is a criterion
variable in the Hypothesis 2 analysis (in which main
effects of sensitivity are also already partialed out) and it
is a mediator in the Hypothesis 3 analysis. Also as noted,
correlations among all variables were clearly less than 1.
Discussion
Results significantly or marginally significantly supported all three hypotheses from our model, evenwhen controlling for a measure of the social aspect of
introversion.
STUDY 2

Figure 3 Relation of adverse childhood parental environment tonegative affectivity for highly sensitive and not highly
sensitive individuals.
NOTE: Difference in slopes, t(91) = 1.50, p = .07 (Study 1, test of Hypothesis 2).

Study 2 addressed three limitations of Study 1: (a) the
Study 1 N was relatively small for testing interaction
effects (perhaps making Study 1’s Hypothesis 2 results
and the Sobel test for Hypothesis 3 only marginallysignificant); (b) because all variables in Study 1 wereassessed as part of the same overall questionnaire packet,
participants may have somehow been affected by theknowledge that the researchers were exploring thesevariables together; and (c) the Study 1 measures of parental environment and negative affectivity were sets of188

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ad hoc items used previously in only one series of studies(Aron & Aron, 1997). Most important, Study 2 provided
the opportunity to replicate Study 1 with a new sample
using different measures of two key constructs.
MethodParticipants were 213 1st- and 2nd-year Stony Brook
psychology students (126 women, 87 men; M age = 19.1).
Inspecting the distribution of sensitivity scores foran appropriate cutoff near the 20% to 35% proportionof highly sensitive individuals expected for psychology
students yielded 48 classified as highly sensitive and 165
not.
Measures included the same sensitivity, shyness, andsocial introversion measures used in Study 1. Four scales
collectively assessed general negative affectivity: The
Beck Anxiety Inventory (Beck, Epstein, Brown, & Steer,1988), the Beck Depression Inventory (Beck, 1978), theaverage rating on 10 negative moods (distressed, upset,
guilty, scared, hostile, irritable, ashamed, nervous, jittery, and afraid) for how much participants “generally
feel this way,” and the three-item negative affectivity scale
used in Study 1 (and Aron & Aron, 1997). Alpha among
the four scales was .88. To assess parental environment,
we used the mother and father versions of Parker,
Tupling, and Brown’s (1979) Parental Bonding Instrument (PBI), in which participants rate 25 statements,“As you remember your mother [father] in your first 16
years of life.” Example items include, “Frequently smiledat me” and “Did not praise me” (reverse-scored). The
PBI has shown strong psychometric properties and has
been validated by correlations with interview data andreports of “objective” childhood events (e.g., Parker,1986). We used the average of the mother and father versions (alphas = .91 and .89; mother-father correlation =.32). (The PBI for each parent is typically scored as two
separate scales; however, following the same logic as inStudy 1, we treated the individual scales and the two parent versions as reflecting causes, not symptoms, of an
adverse childhood environment; see Bollen & Lennox,
1991. Also, again, to the extent these variables might bebetter considered indicators, low internal consistency
would work against our hypotheses.)
Our measures were administered as two separate
questionnaire sets within an overall “mass-testing” session that included numerous paper-and-pencil studies
from other researchers (our two sets always had at least
one other packet between them). One of our sets included the sensitivity and parental questionnaires, andthe other included the shyness, negative affectivity, andintroversion items. The two sets were printed in different
type faces with different styles and page layouts to reinforce the impression that they were from unrelated studies conducted by different researchers.

Figure 5 Relation of adverse childhood parental environment toshyness for highly sensitive and not highly sensitive
individuals.
NOTE: Difference in slopes, t(211) = 1.74, p < .05 (Study 2, test of Hypothesis 1).

Results
Correlations (see Table 1) were similar to those obtained in Study 1, which is notable given that different
measures were used for negative affectivity and parental
environment. Also, all correlations were again substantially and significantly less than 1 (see also Note 5).
Hypothesis 1. We again found the hypothesized interaction, t(211) = 1.74, p < .05. (In this study, there was also
a significant three-way interaction with gender—the pattern was stronger for men.) The two-way interaction wasagain as predicted: For the highly sensitive, the worse theparental environment, the greater the shyness (r = .43);
for the not highly sensitive, this link was much smaller(r = .14) (see Figure 5).
Hypothesis 2. This hypothesized interaction was again
found in Study 2, this time reaching conventional significance levels, t(211) = 2.02, p < .05. For the highly sensitive, the worse the parental environment, the greater thenegative affectivity (r = .50); for the not highly sensitive,
this link was much smaller (r = .21) (see Figure 6).
Hypothesis 3. The results once again met all of Baronand Kenney’s (1986) conditions for the predicted mediation (see Figure 7). Furthermore, this time the direct
test of the mediation (Sobel’s test) was clearly significant, Z = 1.96, p < .05.

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189

Figure 7 Standardized path coefficients for predicting shyness frominteraction of sensitivity and adverse childhood parental
environment, unmediated (top model) and mediated bynegative affectivity (bottom model).
NOTE: In both models, sensitivity and poor parental environment arealso included individually as exogenous variables with effects on the interaction term but are not shown. Mediation (Sobel’s test) Z = 1.96, p <.05 (Study 2, test of Hypothesis 3).
*p < .05. **p < .01.
Figure 6 Relation of adverse childhood parental environment tonegative affectivity for highly sensitive and not highly
sensitive individuals.
NOTE: Difference in slopes, t(211) = 2.02, p < .05 (Study 2, test of Hypothesis 2).

Specificity. As in Study 1, when we repeated each analysis controlling for our social introversion measure, thepatterns of results and significance levels were
unchanged.
Discussion
Study 2, employing various modifications of the Study
1 procedures to strengthen the methodology, replicatedeach of the Study 1 results, including finding clearly significant results for Hypothesis 2 and for Hypothesis 3’s
Sobel’s test.
STUDY 3

To provide yet further replication, we were able toinclude some measures relevant to our model in a questionnaire study conducted by Davies and Aron (2004) on
another topic (the relation of birth order and attachment). That study already included measures of childhood experiences. We were able to add to the packet oursensitivity measure and a brief negative affectivity measure, permitting us again to test, with a new sample,
Hypothesis 2, that the interaction of sensitivity and childhood environment predicts negative affectivity, this timeusing a somewhat different set of measures of childhood
environment.

MethodParticipants were 396 mostly 1st-year undergraduates(196 women, 200 men; M age = 19.0). Inspecting the distribution of sensitivity scores classified 116 as highly sensitive and 280 not. Measures included the sensitivity andthe three-item negative affectivity measures from Studies
1 and 2. Parental environment was assessed with a composite of the mother version of the PBI (Parker et al.,1979) and ratings of actual and desired closeness to themother at ages 5, 9, 13, and 16.
Results
Correlations were all similar to Studies 1 and 2; sensitivity with negative affectivity, r = .46; sensitivity withadverse childhood, r = –.16; and negative affectivity withadverse childhood, r = –.03; all significantly less than 1(see also Note 5). The predicted Hypothesis 2 interaction (the only hypothesis that could be tested in Study 3)
was once again supported, t(389) = 1.69, p < .05. For thehighly sensitive, the worse the parental environment, thegreater the negative affectivity (r = .20); for the nothighly sensitive, this link was near zero (r = –.004) (seeFigure 8).
Discussion
With a new sample and a different combination of
measures of parental environment, Study 3 provided afurther replication of a central element of our model—that the interaction of sensitivity and adverse childhood
experience predicts negative affectivity.

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Figure 8 Relation of adverse childhood parental environment tonegative affectivity for highly sensitive and not highly
sensitive individuals.
NOTE: Difference in slopes, t(389) = 1.69, p < .05 (Study 3, test of Hypothesis 2).

STUDY 4

A basic idea in our model is that highly sensitive individuals are more affected by their childhood environment because they are more affected by all events (Aron& Aron, 1997). Thus, when exposed to an experimentally manipulated negative event, highly sensitive individuals should show a stronger effect on state negative
affect than should not highly sensitive individuals. We
first assessed trait negative affectivity (as a baseline control variable) and sensitivity, next randomly assigned
participants to be subjected or not subjected to a negative event (a frustrating, self-relevant stressor), then measured state negative affect.
MethodParticipants were 160 Stony Brook psychology undergraduates (119 women, 41 men; M age = 20.03) taking
part in the experiment during a regular class session.
Inspecting the distribution of sensitivity scores classified
41 as highly sensitive and 108 not.
All participants completed a brief initial questionnaire—
a six-item version of our sensitivity measure (alpha = .79)
in addition to the three-item trait negative affectivity
measure (which served as a covariate in all analyses) andthe two social introversion items used in previous studies

in this article and in Aron and Aron (1997). (We had tokeep all aspects of the study very brief due to classroom
time constraints.)
When everyone had completed the initial questionnaire, they began the “Iowa Individual Differences Survey,” designed to appear as a completely independent
standardized test packet (e.g., it was printed much moreformally and in different paper and type, it used a quite
different answering format, and it asked for age and sex
again). Participants were told to complete one page at atime and wait for instructions before turning to the next.
Each page was timed. The first two pages were the samefor everyone, were innocuous (page 1, on artistic interests; page 2, on sports knowledge), and the allotted time
was adequate to finish most items.
The next page was the experimental manipulation. It
was labeled “Abilities Survey, Specific Topic: Applied
Reasoning Ability,” with problems adapted from intelligence and scholastic ability tests. For half of the participants, the problems were relatively easy; 84% answered
all or all but one in the allotted time. For the other half ofthe participants, the problems were extremely difficult(one had no correct answer at all); 34% answered all or
all but one. (Comparing percentages, χ2[1, n = 160] =42.15, p < .001; treating proportion as a dependent variable in an overall analysis again yielded a significant version main effect, with no sensitivity main or interaction
effect.)
The next page (“Personality Survey”) was the same foreveryone and contained the dependent variable; three
items (buried among fillers) assessed state negative
affect—feeling “sad,” “anxious,” and “depressed” (alpha = .72).
The final page contained filler items, a manipulation
check item (“How do you think you stand in relation toother people in terms of your applied reasoning ability”), and at the very end, an open-ended item (“Pleasewrite below your best guess as to the overall purpose of
the study”). No participants guessed the purpose, as indicated either by their answer to this item or in-class discussion afterward (before the true purpose was explained).
Results
Manipulation check. Those given the difficult version
rated themselves lower on applied reasoning ability,t(158) = 1.67, p < .05.
Predicted effect. As hypothesized (the analog to Hypothesis 2), the interaction of sensitivity and condition predicted state negative affect (controlling for trait negative
affectivity), t(155) = 1.72, p < .05. There was a clear difference between the two experimental conditions for thehighly sensitive individuals (planned contrast p < .05;
using the Tukey correction, p < .05) but little differenceAron et al. / SENSITIVITY AND SHYNESS

191

lying principle in the model and a result of considerable
interest in its own right (the first experimental study
using the sensitivity measure to show a differential effectin response to a contemporaneous stressor).
GENERAL DISCUSSION

Figure 9 Relation of experiencing a negative event (an experimentallymanipulated stressor) to state negative affect (controlling
for trait negative affectivity) for highly sensitive and nothighly sensitive individuals.
NOTE: Difference in slopes, t(155) = 1.72, p < .05 (Study 4, test of Hypothesis 2 analog).

between conditions for the not highly sensitive (contrast
t < 1). In terms of correlations (to permit comparison toStudies 1-3), for the highly sensitive, having the hard (vs.
easy) test was associated with greater state negative affect(pr = .29); for the not highly sensitive, this link was nearzero (pr = .06) (see Figure 9).
Specificity. All results retained the same pattern andsignificance level after controlling for the social introversion measure. Trait negative affectivity was alreadypartialed out of all analyses. Furthermore, in this study
we were able to evaluate a model that included the interaction of condition and pretest trait negative affectivity
as predictors of state negative affect. In this analysis, thepredicted interaction of condition and sensitivity remained significant and substantial, but the interactionof condition with pretest trait negative affectivity was not
significant (t < 1) and had a near-zero effect size.
Discussion
Sensitive individuals reacted significantly morestrongly than not sensitive individuals to the experimentally manipulated negative experience. On one hand,
this experiment can only be considered an analog to thesituation of growing up in an adverse childhood environment. On the other hand, it is a direct test of a key under-

These four studies provide consistent support for
key aspects of our model of the relation of sensoryprocessing sensitivity to adult shyness. Across three
independent questionnaire studies, we found the
hypothesized interaction of sensitivity and childhood
environment predicting adult trait negative affectivity,and in a fourth, experimental study, we found a paralleleffect in which sensitivity interacted with a manipulated
negative experience to predict greater state negative
affect. Two of our questionnaire studies also tested thelarger implications of the model, with both supporting
the hypothesized interaction of sensitivity with adverse
childhood environment predicting adult shyness as wellas the hypothesis that negative affectivity mediates thisrelation of the interaction to shyness.
Implications
Our first main finding was that highly sensitive individuals are especially more likely to be shy when theyexperienced an adverse childhood environment. Otherwise, they are not more likely to be shy than not highly
sensitive individuals. That is, the childhood-shyness correlation was moderate to high for the highly sensitive but
much smaller for the not highly sensitive. Indeed,inspection of the regression lines for the two groups(Figures 2 and 5) suggests that when highly sensitive
individuals have had a good childhood environment,
they are no more likely (and may even be less likely) to be
shy than are the not highly sensitive. This result is perhaps not surprising given the substantial role thatparenting and peer relationships are known to have on
shyness and the seemingly greater responsiveness of thehighly sensitive to their childhood environment, both
negative and positive (e.g., Boice et al., 1995).
Our second main finding was that, as with shyness,
highly sensitive individuals are especially likely to experience negative affectivity when they had an adverse
childhood environment. In all three questionnaire studies, for the highly sensitive, the childhood-negativeaffectivity correlation was medium to large, but for the
not highly sensitive it was much smaller. The possible
impact of childhood experiences on adult negative affectivity would not seem to be surprising given, for example, the research of Shaver and Brennan (1992), whofound correlations between insecure attachment and
Big Five Neuroticism. And a stronger impact on highly
sensitive individuals is also no surprise given the re-192

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search reported by Gunnar (1994) and Nachmias et al.
(1996) and our own suggestive results (Aron & Aron,
1997) reviewed in the Introduction. Furthermore, theexperimental study, although only an analog with regard to childhood environment, provides evidence for astronger causal effect of negative experiences on negative affect for those who are highly sensitive.
Our final main finding is that the stronger link ofadverse childhood environment to shyness among thehighly sensitive is largely accounted for by a greater linkof childhood environment to negative affectivity. That is,in both studies assessing shyness, the interaction effect ofchildhood environment and sensitivity on shyness wasmediated by negative affectivity. This finding is consistent with our model and makes sense in light of the findings that the more an emotionally relevant experience isprocessed, the more emotion is felt (Tesser, 1978) andthat the highly sensitive seem to show more negative andpositive affectivity (Aron & Aron, 1997). If they process
all experiences more deeply, and if the preponderanceof their experiences are negative, it follows that theiraffect should be more negative, which in turn should
lead to more negative expectations in social situations.
Methodological Strengths and Weaknesses
Strengths include the replications across as many asfour separate samples, the use of established measuresfor each major variable in at least one of the studies, theprocedure in Studies 2 and 4 making it appear that key
variables were being assessed as parts of separate studies, the experimental manipulation in Study 4, and theclearly consistent pattern of results across all fourstudies—including moderation effects that are notoriously difficult to identify in regression designs(McClelland & Judd, 1993) and finding the same interaction in an experiment in which circumstances limited
us to a relatively weak manipulation and relatively weakmeasurement of our dependent variable.
One key limitation of the questionnaire studies (Studies 1-3) is that they are purely correlational and crosssectional, so it is not possible to draw unambiguous conclusions about direction of causality. It is encouraging
that the statistically complex pattern of results (twomoderations and a mediated moderation) were entirely
consistent with the model. Furthermore, we attempted avariety of alternative models that yielded poorer results.
For example, in Studies 1 and 2 where we tested the
mediation model, the alternative possibility that shyness
is the mediator between the interaction and negative
affectivity was not significant, and neither were a variety
of models in which negative affectivity was taken as theexogenous distal cause. The causal direction from theinteraction to negative affectivity is also strengthened byStudy 4, where we manipulated negative experience. In

addition, in that experiment, there was a robust effect of
the interaction of condition and sensitivity, but there wasa near-zero effect size for an alterative model of the interaction of condition and pretest trait negative affectivity.
Nevertheless, the possibility that the underlying relation
among our variables follows a causal order other thanwhat we have proposed cannot be ruled out conclusively
with the present studies.
A related issue concerns the distinctiveness of our key
variables from each other. The consistently, substantiallybelow unity correlations among our measures makesomewhat unlikely the possibility that these four variables (or some subset of them) are actually alternative
operationalizations of a single underlying construct (seealso Note 5). Furthermore, suppose sensitivity and negative affectivity or shyness actually are the same thing
under different names or that they represent some common underlying negativity variable. (This would meanthat having high scores on both sensitivity and negativity
affectivity or shyness would be associated with stronger
relationships with other variables.) Such a scenario, however, implies a pattern of results quite different fromthose hypothesized and found in these four studies. For
example, suppose it is proposed that such a common
underlying variable is unrelated to childhood environment or negative experiences (as might be the case if
such a common variable were entirely biologically
based). With these assumptions, the predicted effect on
negative affectivity or shyness would be a main effect forsensitivity, with no main effect for childhood (see Figure10b)—a pattern quite different from that predicted andfound in the present studies (see Figure 10a). Or, suppose it is proposed that such a common variable isstrongly related to childhood experience (as might be
the case if such a common variable were entirely environmentally based). With these assumptions, the prediction
would be for two main effects (see Figure 10c), again aresult quite different from the interaction we hypothesized and observed in this research.
Another issue is that, with the exception of the manipulated negative experience in Study 4, the studies
employed entirely self-report measures. Thus, correlations among variables might be due to common method
variance such as common general response bias effects.
This interpretation, however, as noted in the Introduction, is made relatively unlikely by the moderational andmediational findings, all of which require partialing out
one or more other self-report variables. That is, the obtained pattern of findings hold up over and above any
general patterns of common biases or common method
variance.
Perhaps the greatest methodological concern inthese initial tests of our model is that the measures ofchildhood environment were entirely retrospective.

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193

Figure 10 (a) The model’s predicted pattern of results for the interaction of sensitivity with adverse childhood environment for predicting shyness
or negative affectivity. (b) Alternative pattern of results predicted from the assumption that sensitivity and shyness or negative affectivity
reflect a common underlying variable that is primarily biologically based. (c) Alternative pattern of results predicted from theassumption that sensitivity and shyness or negative affectivity reflect a common underlying variable that is primarily environmentally
based.
NOTE: Actual results across four studies and six comparisons followed the pattern shown in (a) and not the patterns shown in (b) or (c).

However, the pattern of our significant interaction
effects would seem to undermine alternative explanations in terms of systematic negative recall bias (e.g.,
Cutler et al., 1996; Feldman, 1993; Larsen, 1992). For
example, negative recall bias for those with negative
affectivity or shyness would imply a main effect for childhood but no main effect for sensitivity (see Figure11b)—a quite different pattern of results from the one
we hypothesized and found (see Figure 11a). The possibility that sensitivity also creates a recall bias for childhood events seems unlikely given that the correlations ofsensitivity with adverse childhood in our studies were allsmall (.16, –.03, and –.16), averaging near zero. If one
nevertheless insisted that there might be such a bias inspite of these low correlations, the implications would be
for a very different pattern of results than we observed.
That is, this situation would imply two main effects, one
for childhood and one for sensitivity (see Figure 11c). (Itmay seem counterintuitive at first that the highly sensitive line in Figure 11c is below the line for the not highly
sensitive. It works this way because, with the supposed
added recall bias due to sensitivity, it would take less bias
from negative affectivity or shyness to produce the same
degree of overall bias in reports.)194

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Figure 11 (a) The model’s predicted pattern of results for the interaction of sensitivity with adverse childhood environment for predicting shyness
or negative affectivity. (b) Alternative pattern of results predicted from scenario in which reports of adverse childhood are entirely afunction of negative recall bias associated with shyness or negative affectivity (but not sensitivity). (c) Alternative pattern of results
predicted from scenario in which reports of adverse childhood are entirely a function of negative recall bias associated with both shyness
or negative affectivity and sensitivity. (d) Alternative pattern of results predicted from scenario in which reports of adverse childhood are
entirely a function of negative recall bias associated with both shyness or negative affectivity and sensitivity and in which the combinationof both kinds of bias creates a larger effect than the sum of the two biases.
NOTE: The circled 1 refers to Person 1, a data point on the line for highly sensitive individuals; the circled 2 refers to Person 2, a data point on theline for the not highly sensitive. These two data points vary in sensitivity but have equal levels of shyness or negative affectivity (about 3 in this example). In the pattern that was predicted and found in a, Person 1, although highly sensitive, actually would have to have a less adverse childhood than
Person 2 to be at the same level of shyness and negative affectivity. In the main recall bias scenarios, using (c) as an example, Person 1, the highly sensitive individual, would be predicted to have reported a more adverse childhood than Person 2. But this did not happen—the actual results acrossfour studies and six comparisons followed the pattern shown in (a) and not the patterns shown in (b), (c), or (d).

Indeed, as noted briefly in the Introduction, the ideaof greater recall bias for those who are highly sensitive
implies exactly opposite results from those we hypothesized and found. It may be helpful to expand briefly on
this point here. Consider two persons located at thesame place on the vertical axis, that is, with equal levels ofnegative affectivity and shyness. One (whom we will call
Person 1) is a person or data point on the line for highly
sensitive individuals and one (Person 2) is found on theline (i.e., a data point on the line) for not highly sensitive
individuals. In the scenario in which sensitivity creates arecall bias (see Figure 11c), if Persons 1 and 2 have thesame level of negative affectivity and shyness, then Person 1 must have reported a more adverse childhood than
Person 2. But in the pattern we predicted and found,
Person 1 reports a less adverse childhood than Person 2.
(That is, our model hypothesizes that a highly sensitive
individual, compared to a not highly sensitive individual,

Aron et al. / SENSITIVITY AND SHYNESS
requires a less adverse childhood to have the same degree of negative affectivity or shyness.)
What if the supposed recall bias effects of negative
affectivity or shyness and sensitivity are not merely additive but are interactive such that when one has both negative affectivity or shyness and sensitivity, one has greater
recall bias than would be expected by just their sum?
This scenario (see Figure 11d) implies an interaction,
but a quite different interaction than we predicted andfound (see Figure 11a). (Our results could be predicted
if the sum of the two biases was somehow less than the
total, as might happen if there was a ceiling or floor effect on one or more of our variables. However, there wasno sign of such a floor or ceiling effect on any of them.)8
In addition to the above considerations, we would
also again note that (a) our interpretation of the general
pattern of results in terms of negative experience interacting with sensory-processing sensitivity to create negative affectivity is supported by the experimental results,
where recall bias regarding negative experiences is not
an issue, and (b) the measures in Studies 1 and 2 included mainly relatively “objective” indicators and independent research on the Parental Bonding Instrumentused in Studies 2 and 3 found it correlated with reports ofother relatively objective childhood events (Parker, 1986).
Conclusions
These four studies provide consistent and substantial
initial support for a novel model of the relation of origins of adult shyness, such that the interaction of sensoryprocessing sensitivity and adverse childhood environment leads to negative affectivity, which in turn leads toshyness. These findings do not seem easily entirely
explained away as due to alternative directions of causality, common method variance, or systematic recall bias.
At the same time, our results should be taken as only the
first step, pending further research such as studies employing longitudinal designs and less direct measures. In
addition, any generalizations beyond North Americancollege students must be made with caution.
Nevertheless, if future research continues to support
this model, it would have significant theoretical implications for understanding the development of shyness andnegative affectivity and the nature of sensory-processing
sensitivity and related variables. It also could have significant practical implications for child rearing, psychotherapy, and the treatment of social phobia.
NOTES
1. Aron and Aron (1997) argued that “sensory-processing sensitivity” is preferable to these other terms. For example, “reactivity” is acharacteristic of all, so that what is implied is overreactivity, andwhether a stimulus is being noticed more than is adaptive depends on
the situation. Threshold of responsiveness seems to rule out the processing aspect of the trait, the preference to pause and process. As for

195

innate fearfulness or inhibitedness, three points argue against theseterms. First, Gray (1985) points out that innate fearfulness would
explain a greater sensitivity to threatening stimuli but not to all stimuli.
Second, natural selection would purge alleles that created inappropriate reactions to situations (Harpending & Cochran, 2002), as would be
the case if the trait were general fearfulness. Third, Aron and Aron’s
adult data (reviewed briefly below) found a partial independence ofsensory-processing sensitivity from negative affectivity in general (as do
the data reported in this article).
Nevertheless, the distinctiveness of sensory-processing sensitivity
from each of these other individual difference characteristics remains
an open question. Thus, the role of sensory-processing sensitivity in the
proposed model is consistent with the possibility that it is more appropriately labeled as one of these other constructs.
2. We treat negative affectivity as an overarching individual difference including both anxiety and depression because they operate similarly in our model. However, there is also evidence that they may moregenerally represent a relatively unitary characteristic (e.g., Feldman,1993).
3. Experiencing the social and cultural unacceptability of being
highly sensitive (Chen, Rubin, Sun, 1992), especially for boys (seeCheek & Krasnoperova, 1999; Henderson & Zimbardo, 1999;
Stevenson-Hinde & Hinde, 1986), no doubt adds to the environmental stressors and fear of social evaluation. Aron (1999) foundsomewhat lower self-esteem in sensitive adults whatever the qualityof their childhood experiences, although the interaction again
appeared—self-esteem was still lower for sensitive adults with an adverse childhood.
4. Such conditions might themselves be genetically influenced in
the parents so that an interaction with sensitivity could represent aninteraction of two genetic variables (which would be an interestingfinding in its own right). However, Study 2 combines these indicatorswith other kinds of measures, Study 3 does not use these indicators
at all, and Study 4 uses a conceptually related manipulated variable.
Thus, results consistent across studies (as was found) would seem toundermine such interpretations.
5. In each questionnaire study (Studies 1-3), we tested the relation
among childhood environment, sensitivity (treated here as a continuous variable so we could make it a latent variable), negative affectivity,and shyness (except in Study 3, where shyness was not measured) using
structural equation modeling (SEM). Every correlation among theselatent variables was significantly less than 1, and all one-factor, twofactor, and three-factor models showed a significantly worse fit than thefull three- or four-factor model (all ps < .0001).
6. For each hypothesis test in the questionnaire studies (Studies 13), we conducted parallel latent variable SEM analyses. The interactions were examined in the standard way in SEM (Jaccard & Wan,
1996) using a multiple-group model (highly sensitive and not) andtesting whether the model became significantly worse when the path tobe moderated (childhood environment to shyness or to negative
affectivity) was constrained to be equal across groups. In every case (forall interaction hypotheses tested in all three studies), the pattern was
the same and with at least the same significance level as the ordinary
regressions reported in the main text. The Hypothesis 3 mediations
could not be tested directly in SEM with latent variables, but these
mediation models all showed the predicted pattern. Also, there was an
excellent fit of the overall models for all hypotheses in all studies (e.g.,
in all cases, the high 90% Confidence Interval [CI] for the root meansquare error of approximation [RMSEA] was ≤ .07).
7. Some leniency in alpha level seems appropriate given the low
power of regression interactions (McClelland & Judd, 1993). We areparticularly confident here given that the parallel interaction reachedconventional significance levels in Studies 2 through 4.
8. Also, all of the common underlying variable scenarios (e.g., Figure 10c) with the recall bias scenarios (Figures 11b-d) imply interaction patterns quite different from those we hypothesized and obtained.
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Received February 18, 2003
Revision accepted May 4, 2004