Sensitivity to Affective Touch Depends on Adult Attachment Style

Affective touch supports affiliative bonds and social cognition. However, it remains unknown whether pre-existing models of social relating influence the perception of affective touch. Here, we present the first study (N=44) to examine how individual differences in attachment styles relate to the perception of affective touch, as well as to a different non-social modality of interoception, namely cardiac perceived accuracy. Using the gold standard assessment of adult attachment (Adult Attachment Interview), we found that insecure attachment was associated with reduced pleasantness discrimination between affective vs. non-affective, neutral touch. Acknowledging the different traditions in measuring attachment, we also used a well-validated self-report questionnaire that pertains to explicit representations of current close relationships. Using this measure, we found that higher scores on an attachment anxiety dimension (but not an attachment avoidance) were associated with reduced pleasantness discrimination between affective vs. non-affective, neutral touch. Attachment patterns (in both measures) were not related to cardiac perception accuracy. These results corroborate and extend previous literature on the affectivity of touch and its relation with affiliative bonds and social cognition. Given that attachment was not related to perceived cardiac accuracy, these findings point to the specificity of the relationship between affective touch and attachment.

development of IMW, show selective behavioural and physiological sensitivity to stroking touch at 'CT-optimal' velocities as compared to similar but 'non CT-optimal' velocities (< 1cm/s -1 and > 10cm/s -1 ) 44 . Indeed, the notion that the neural substrate for detecting pleasure associated with this kind of touch develops early has been supported by recent findings suggesting that gentle touch at CT-optimal speeds in newborns leads to increased BOLD activity in brain regions associated with the socio-affective processing of touch (i.e., postcentral gyrus 45 and insular cortex 45,46 ). A recent behavioural study further found that this type of touch helps infants tune to social signals, such as faces, more than other types of touch 47 . These findings support the idea that the CT system may form part of a dedicated interoceptive modality conveying affective and affiliative aspects of social touch and thus promoting the development of self-awareness and affect regulation in early development 24 .
In adults, stroking touch at CT-optimal velocities, as compared with non-optimal velocities, has been shown to specifically communicate social intimacy and support 28 , to reduce experimentally-induced feelings of social rejection 29 and subjective and neural responses to noxious stimulation 48 , as well as to contribute uniquely to embodied facets of self-awareness 49-51 . Nevertheless, the relationship between CT-optimal stimulation, autonomic regulation, and interoception remains unclear in adults, as CT-optimal touch is specifically associated with reductions in cardiac reactivity and skin conductance responses 52 , but not other measures of Attachment style and affective touch 7 autonomic reactivity, such as cortisol variability 53 , or interoceptive awareness such as heart rate awareness 50,53 . Despite the increasing emphasis in the literature on the relationship between interoceptive awareness and emotion regulation, such mixed findings in adult cohorts are not uncommon (see 54,55 for discussion). It is indeed increasingly recognized that while sensing of bodily signals (interoception) is a fundamental facet of our emotional experience, the explanatory power of heartbeat detection accuracy only weakly predicts an individual's vulnerability to anxiety or other affective disorders. Instead, it appears that in order to specify the role of interoception in personality and psychopathology, models need to account for the relationship between bottom-up (e.g., interoceptive accuracy abilities) and top-down (cognitive beliefs, styles, and expectations) factors. Accordingly, this study aimed to characterize individual differences in affective touch and cardiac awareness in terms of differences in pre-existing models of social interactions, namely attachment styles.
Indeed, if affective touch is an interoceptive modality particularly relevant to social affiliation and affect regulation, one can presume that the perception of affective touch in adulthood can further depend on individual differences in attachment. As pre-existing affectivecognitive models of social relating, individual differences in attachment style could determine the top-down influences on the perception of affective touch. Such findings exist in other interoceptive modalities such as hunger 56 and pain (reviewed by 57,58 ), the latter being an interoceptive modality with opposite hedonic (positive vs. negative valence) and social (care vs. harm) characteristics to affective touch (see 59 for discussion). For example, chronic pain is more common in individuals with insecure (characterized by early interpersonal experiences of inconsistent and unreliable caregiving) rather than secure attachment styles (characterized by comfort in closeness and consistent, reliable caregiving 57 ). We have also previously shown that Attachment style and affective touch 8 the effects of social support on subjective, physiological and neural responses to pain, including support conveyed by CT-optimal touch 48 , depend on individual differences in attachment style 48,60,61 .
However, to our knowledge, the relationship between attachment style and sensitivity to affective touch has not yet been studied. Here, we present the first study to examine how attachment style relates to the perception of affective touch, as well as to a different non-social modality of interoception, namely cardiac sensitivity. Specifically, acknowledging the possible continuity of attachment styles from childhood to adulthood and taking into account different research traditions in measuring attachment (see 62 for a review), we examined attachment using two different measures. First we administered the gold standard Adult Attachment Interview (AAI 63 ). Developed in the context of early, classic research into attachment styles (Main et al., 1985) and thus taking a categorical approach, this semi-structured interview yields secure vs.
insecure attachment classifications (as well as further sub-classifications of attachment characteristics such as insecure preoccupied and insecure dismissive) on the basis of questions relating to childhood experiences with caregivers. In addition, we used a well-validated selfreport questionnaire (the Experiences in Close Relationships Revised questionnaire 64 ). This questionnaire pertains to adult romantic relationships and takes a dimensional rather than categorical approach. In line with theory and research suggesting that adult attachment styles are best conceptualised as dimensional constructs 65 , this questionnaire yields continuous scores of attachment anxiety and avoidance (lower scores denoting greater attachment security and higher scores greater insecurity). Attachment anxiety is characterized by a need for emotional closeness, worries of rejection and abandonment, over-dependence on others, negative views of self, positive views of others, and high emotional reactivity. Attachment avoidance is characterized by Attachment style and affective touch 9 a need for emotional distance, resistance to trusting and depending on others, positive views of self, negative views of others, and suppression of emotion.
Given their history in seeking comfort through proximity, we expected that securely attached individuals, based on a categorical AAI classification, would find affective touch (at CT-optimal speeds) more pleasant than non-affective, neutral touch (at non-CT-optimal speeds).
By contrast, we expected that insecurely attached individuals (associated with reduced proximity-seeking in the case of dismissive attachment, or truly obtaining comfort through proximity, including touch, in the case of preoccupied attachment) would be less sensitive to affective touch, that is, they would show reduced perceived pleasantness discrimination between the two types of touch. Exploring such differences further using a continuous measure of adult attachment style, we expected that this reduced sensitivity to the hedonic effects of affective (CT-optimal) and neutral (non-CT-optimal) touch would be especially pronounced in individuals scoring higher in anxious and avoidant attachment dimensions, given their typical negative feelings and beliefs about seeking, or receiving social support 66 .
In addition, to investigate whether the relationship between insecure attachment and affective touch sensitivity is specific to this modality, or whether it relates to all interoceptive domains, we also employed a widely-used task of heartbeat counting as a measure of 'interoceptive accuracy', a particular facet of interoceptive awareness (see 67 ). Given previous findings about the dissociation between cardiac accuracy and affective touch 50,68 , we expected that attachment style, as measured by both categorical and continuous measures, would not relate to cardiac perceived accuracy as measured by the standard heartbeat perception task, confirming the specificity of affective touch to social bonding and attachment.

Touch paradigm
A trained experimenter unknown to participants manually stroked participants' left forearm using a cosmetic make-up brush (Natural hair Blush Brush, No 7, The Boots Company).
Participants were seated comfortably at a computer, with their left forearm rested at an approximate 45° angle in front of them (their palm facing upwards) but separated from their view by means of a curtain. Two 9cm long by 4cm wide areas were marked continuously along participants' left volar forearm between wrist and elbow. To ensure a constant pressure, the brush splayed no wider than the 4cm window. Touch was administered to the underside of Attachment style and affective touch 11 participants' left forearm in an elbow-to-wrist direction 69,70 at four different velocities, administered in a pseudo-randomized order and alternating between skin areas to avoid habituation: two CT-optimal speeds i.e., 3cms -1 and 9cms -1 and two non-CT-optimal speeds i.e., 0.3cms -1 and 27cms -1 . Each velocity was administered for 9s, followed by a 30-second interval during which participants rated the pleasantness of the touch on a scale from -100 (very unpleasant) to 100 (very pleasant). Each velocity was administered three times and a mean rating was calculated for each velocity.

Interoceptive accuracy
We measured interoceptive accuracy using the heartbeat perception task 71 . Participants' heart rate was recorded using MP150 Data Acquisition Hardware (BIOPAC Systems Inc). A heartbeat monitor was attached to the tip of the left index finger and checked for tightness so that participants could not feel a pulse at this site. During a short training session participants were instructed to report the number of perceived heartbeats within a 15 seconds time interval. They were explicitly told to only count and report the number of actually perceived (and not estimated) heartbeats. The experiment started with a 10 second resting period. Participants closed their eyes and then silently counted their heartbeat (keeping their hand still and without feeling their pulse) for three trials lasting 25 seconds, 35 seconds and 45 seconds; the order was pseudorandomised and participants were not informed of the duration of each trial. The beginning and end of each counting interval was signaled via tones. There was a 20 second pause after each trial during which participants verbally indicated their count for each trial. Interoceptive accuracy was computed using the mean score of the three heartbeat counting trials, using the transformation detailed in 71 (see formula also below).

Attachment style and affective touch 12
This yields a score between zero and one, with one denoting greater correspondence between actual and perceived number of heartbeats i.e., higher interoceptive accuracy.

Adult attachment interview (AAI; George et al., 1996)
The AAI is a semi-structured interview, including 20 questions and lasting up to circa one hour. Meta-analyses and psychometric testing indicate stability, and discriminant and predictive validity in both clinical and non-clinical populations 62,[72][73][74] . Participants were asked to reflect about their childhood experiences and early relationships with parents/caregivers. Questions included whether participants had experienced loss, separation or rejection, how their caregiver typically responded in particular situations e.g., when the participant was upset, and the kinds of implications these experiences had for the participant's adult life (see 72 for a detailed introduction to the AAI). All interviews were audio recorded and transcribed verbatim (including pauses). A trained coder (C.V.) coded all interview transcripts and classified participants as secure, dismissive, preoccupied, or unresolved, which allowed us to categorize participants as either securely or insecurely (dismissive, preoccupied, unresolved) attached i.e., our main two categories of interest. A second trained coder (T.N.) independently coded 25% of interviews.
Agreement between the two coders was perfect (Cohen's kappa = 1) for the secure vs. insecure classification. Six participants did not attend the AAI session; hence, n = 38 participants were included in these analyses.

Self-report measure of adult attachment style (Experiences in Close Relationships Revised -ECR-R; Fraley et al., 2000)
The ECR-R comprises 36 items rated on a 7-point scale (1 = strongly disagree and 7 = strongly agree) regarding the general experience of intimate adult relationships; 18 items pertain to attachment anxiety (e.g., "I'm afraid that I will lose my partner's love.") and 18 to attachment Attachment style and affective touch 13 avoidance (e.g., "I don't feel comfortable opening up to romantic partners."). Item responses are averaged (after reverse-scoring appropriate items) separately for each subscale to produce a mean score for attachment anxiety and attachment avoidance, with higher scores denoting greater attachment insecurity. This dimensional scoring is in line with research indicating that adult attachment styles are best conceptualised as dimensional constructs 65 . The ECR-R is wellvalidated 62,75 and demonstrates excellent internal consistency: Cronbach's α = .91 for attachment anxiety and α = .90 for attachment avoidance in the present sample.

Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Relationship Between Affective-Neutral Touch Discrimination and Interoceptive
(Cardiac) Accuracy. Affective-neutral touch discrimination (operationalised as a difference score of CT-optimal velocities minus non-CT-optimal velocities, i.e., greater scores denoting higher pleasantness ratings for CT-optimal vs. non-CT-optimal touch) was not significantly correlated with interoceptive (cardiac) accuracy, r = .21, p > .05.

Main Analyses
Association between interview-assessed attachment style (AAI classification) and the perception of affective touch. To examine whether attachment classification as measured by the AAI was associated with the perception of affective touch, we specified a multilevel regression model with mean pleasantness rating as the outcome variable and velocity (CT-optimal vs. non-CT-optimal), AAI (security vs. insecurity), and their interaction as predictor variables, and controlled for interoceptive accuracy. A random effect was included to account for the repeated assessment of the outcome variable within individuals.  Table 1 for full model results). Follow-up tests showed that the difference between CT-optimal and non-CT-optimal velocities was significant for securely attached participants (b = 49.01, SE = 4.08, p < .001), and insecurely attached participants (b = 28.19, SE = 8.44, p = .001). However, the difference in pleasantness ratings for CT-optimal and non-CT-optimal velocities was smaller for insecurely vs. securely attached participants (see adjusted mean difference above and Figure 2 047. Therefore, although both groups were able to discriminate between the two forms of touch, attachment insecurity was associated with reduced discrimination between CT-optimal and non-CT-optimal touch, in line with our hypothesis.

Association between questionnaire-assessed attachment style (ECR-R) and the perception of affective touch
To test whether attachment style dimensions as measured by the ECR-R questionnaire were associated with the perception of pleasant touch, we specified a multilevel regression model with mean pleasantness rating as the outcome variable, and velocity (CT-optimal vs. non-CToptimal), ECR-R attachment anxiety, ECR-R attachment avoidance, as well as all interaction terms, as predictor variables, and again controlled for interoceptive accuracy. As above, a random effect was included to account for the repeated assessment of the outcome variable within individuals.
Neither attachment anxiety nor attachment avoidance, nor the interaction between the two dimensions were associated with pleasantness ratings across velocities, indicating that pleasantness of touch in general was not influenced by continuous attachment style scores.
However, importantly, the hypothesised velocity by attachment anxiety interaction was significant (see Table 1 for full model results). Follow-up analyses revealed that the difference between CT-optimal and non-CT-optimal velocities was significant at lower (i.e., -1SD; b = -53.06, SE = 5.12, p < .001), moderate (i.e., mean; b = -44.32, SE = 3.52, p < .001) and higher (i.e., +1SD; b = -35.58, SE = 5.24, p < .001) levels of attachment anxiety. Similar to the AAI results, the difference in pleasantness ratings between CT-optimal and non-CT-optimal velocities was smallest at higher levels of attachment anxiety (see adjusted mean difference above and Figure 2, bottom panel). This finding indicates that higher attachment anxiety was associated Attachment style and affective touch 18 with reduced discrimination between CT-optimal and non-CT-optimal touch. The velocity by attachment avoidance interaction was non-significant, as was the three-way velocity by attachment anxiety by attachment avoidance interaction. Thus, attachment avoidance was not associated with the perception of affective touch, either alone or interaction with attachment anxiety. In sum, partially supporting our hypothesis, higher attachment anxiety but not attachment avoidance was associated with reduced sensitivity to affective touch. Note. AAI = Adult Attachment Interview; ECR-R = Experiences in Close Relationships -Revised questionnaire.

Figure 2. Interactions between velocity (CT-optimal vs. non-CT-optimal) and attachment classification on the Adult Attachment Interview (AAI; top panel), and velocity and attachment anxiety measured using the Experiences in Close Relationships -Revised questionnaire (ECR-R; bottom panel). Error bars represent ±1 standard error of the mean.
Attachment style and affective touch 20

Discussion
We reported the first study investigating the association between attachment styles and affective touch in adulthood. Under the assumption that affective touch supports affiliative bonds and social cognition, we assessed how affective-cognitive models of social relating (i.e., attachment) influence the perception of affective touch. Using the gold standard assessment of adult attachment (the Adult Attachment Interview; AAI), we found that insecure attachment was associated with reduced discrimination between affective vs. non-affective, neutral touch. This semi-structured interview yields categorical attachment classifications in an implicit way, relating to representations of childhood experiences with caregivers. Acknowledging the different traditions in measuring attachment and the multi-dimensionality of this construct, we also used a well-validated self-report questionnaire that pertains to explicit evaluations of close relationships and takes a dimensional rather than categorical approach. This measure showed that higher attachment anxiety, though not higher attachment avoidance, was associated with reduced discrimination between affective vs. non-affective, neutral touch. Attachment style as assessed by both measures was not related to cardiac perception accuracy, suggesting that attachment is not relevant to all interoceptive modalities in the same way. These results will be discussed in turn below.
We found that both secure and insecure attachment groups (assessed by the AAI) were able to discriminate between affective vs. non-affective touch. However, the insecure attachment group was significantly worse in this discrimination than the secure group, suggesting that differences in pre-existing models of social interaction and related top-down expectations contribute to individual differences in affective touch perception. This finding provides further support to theoretical proposals regarding an association between the perceived affectivity of Attachment style and affective touch 21 touch and social affiliation 24,42,43,59 . Attachment representations are thought to originate in early caregiving experiences, in which touch plays a central part 9,10 . There is also evidence that childhood patterns of social relationships may be reinforced across the lifespan 5 and it thus appears that affective responses to touch are also carried into adulthood.
Differences in attachment (as measured by the AAI) were not related to cardiac accuracy.
To date, there is no evidence to suggest that cardiac awareness is an interoceptive modality relevant to social affiliation and thus pre-existing models of social relating, such as attachment classifications, were not predicted to influence this interoceptive modality. This finding also speaks to the more general relationship between interoceptive modalities. In other studies, our group and others have shown that the perception of social, affective touch and cardiac perception accuracy are unrelated 50,68 . The current findings confirm this and further suggest that differences in attachment relate to the perception of affective touch but not cardiac perception accuracy.
Turning to our second two-dimensional measure of attachment style, we found that higher scores in attachment anxiety were related to poorer discrimination between affective and non-affective touch. This finding suggests that anxious attachment style as assessed by an explicit measure of adult close relationships relates to the perceived affectivity of touch in a similar way to insecure attachment as assessed by the AAI. In insecure attachment, others are perceived as unreliable and inattentive, and particularly in anxious insecure attachment this might generate anxiety 78 . These kinds of social expectations might thus affect the way in which affective touch is perceived and enjoyed. Consistent with recent research suggesting that infants as old as two months old show selective sensitivity to affective touch 45,46 , we hypothesized that any difference in this discrimination in adulthood based on attachment styles would relate to topdown effects. Indeed, we also observed that insecure attachment style was related to the overall Attachment style and affective touch 22 perceived pleasantness of our tactile stimuli, irrespective of whether or not they were in the CToptimal range.
The fact that we did not observe differences in discrimination in our questionnaire dimension of attachment avoidance was unexpected, particularly as these individuals are characterized by a need for emotional distance and reduced proximity-seeking, including touch 62,79,80 . This null finding thus suggests that at least at an explicit level, current top-down representations of close relationships in these individuals may not determine the perceived affectivity of touch. However, future research is needed before drawing firm conclusions. Here, we propose a few candidate explanations that may have led to such a lack of findings. First, although measurements of attachment style may possess benefits at a theoretical and statistical level, self-reported questionnaires have been largely criticized for being passive, i.e., not detecting attachment phenomena that need to be activated to be manifested 62 . As such, this may have contributed to the current lack of findings. Also, as self-report measures, they are subject to social desirability effects, which are likely to be more pronounced in more avoidantly-attached individuals.
Finally, as with our other implicit measure of attachment, we found that individual differences in attachment style (as measured by the questionnaire dimensions) were not related to cardiac accuracy, suggesting that cognitive more models of current close social relationships and related top-down expectations do not contribute to individual differences in cardiac interoceptive perception. Given that individual differences in attachment style were related to the perceived affectivity of the touch and not cardiac accuracy, this finding provides further support to the specificity of the relationship between affective touch and attachment style.
Attachment style and affective touch 23 Our findings should be considered in light of their limitations and directions for future research. First, it should be noted that there were no differences in the attachment anxiety or avoidance questionnaire scores between the secure and insecure AAI groups. This finding, together with prior research suggesting a trivial to small relation between self-report measures of attachment and the AAI 81 , speaks to the different aspects captured by each of these measures and consequently supports the choice of two separate measures for this multi-dimensional construct.
Second, on the AAI, small numbers in the insecure attachment group meant we were unable to further compare preoccupied vs. dismissing individuals. Future studies could aim to recruit larger groups of preoccupied and dismissing individuals to examine whether results on the insecure group may have been driven by preoccupied or dismissive individuals (although interestingly, the largest subgroup in the insecure AAI classification was dismissive; in line with the general population AAI norms 73,76 ). Third, pleasantness ratings for the affective touch velocities overall fell in the middle of the positive side of the response scale; it is likely that touch by an attachment figure, such as the romantic partner, may feel even more pleasant to participants than touch by an experimenter. Similarly, the current effects on affective vs. non-affective touch discrimination may be subject to social context, in which for instance, touch by an attachment figure could activate attachment behaviors that are not always at display (see 62 ). Thus, future research could incorporate partner-administered touch. Finally, we only tested women in order to control for gender effects associated with the perception of touch 70,82,83 ; however, future research is needed to examine whether the present results extend to men.
In sum, the present study corroborates and extends previous literature on the affectivity of touch and its relation with affiliative bonds and social cognition. Given that attachment style (in both measures) was not related to perceived cardiac accuracy, these findings point to the Attachment style and affective touch 24 specificity of the relationship between affective touch and attachment style. Future work is needed to examine the role of social context and whether the present results extend to men.