fifty - one healthy participants ( 36 female ; mean age = 37.81  years , sd = 17.07 , range = 1865 ) completed the ug and the interoception task . all of the participants were in the normal iq range ( mean = 118.15 , sd = 8.81 , range 93.40130.60 ) , which was estimated using the national adult reading test ( nelson , 1982 ) . age , gender , and iq were not significantly related to overall , computer , or human rejection rates ( greatest r = .23 ; smallest p = .10 ) . the study was approved by the cambridge university psychology research ethics committee , and all participants gave written informed consent prior to taking part . volunteers were given an honorarium of  6 per hour for their time and were awarded  3 to cover travel expenses . the ug was as described in ( dunn , makarova et al . , 2010b ) . participants played the role of responder in 20 one - shot ugs offering a division of  10 . there were 10 fair (  5 ) , two slightly unfair (  3 ) , four moderately unfair (  2 ) , and four very unfair (  1 ) offers , presented in a random sequence . participants were told that 50  % of each offer type was proposed by previous participants , and the other half was generated randomly by the computer ( in reality , the offers were determined by the experimenter and were fixed across all participants ) . on each trial , a fixation cross was displayed , the proposer or the computer was shown , and the offer was presented ( 10  s each ) . participants then responded to the proposal , before feedback was delivered for 10  s. as a manipulation check , after completing all 20 ug trials , participants retrospectively rated how angry each offer type made them feel and how fair each offer was , on a scale from 0 ( not at all ) to 100 ( extremely ) . we chose not to take anger and fairness ratings immediately after each trial , because we did not want these ratings to influence subsequent rejection behavior . prior to the responder trials , all of the participants also made five proposals for future players on the task and had their photographs taken . this approach was taken to make it believable that the human offers that participants received were made by real people . to keep participants highly motivated , they were instructed that one of their twenty responder decisions would be chosen at random to be paid out on , meaning their decisions were not purely hypothetical . interoceptive accuracy was measured using the schandry ( 1981 ) heartbeat perception task as described in ( see dunn et al . , participants counted how many heartbeats they felt over a period of time ( 2  35  s , 2  25  s , and 2  45  s ) , and this was compared to how many heartbeats occurred on a simultaneous ecg trace . to control for the possibility that participants performed the mental tracking task by counting time and then making an educated guess according to underlying beliefs about hr ( ring & brener , 1996 ) , we took two steps . in three time - estimation trials ( 1  23  s , 1  56  s , 1  40  s in length ) participants were asked to count how many seconds elapsed between two tones , with estimates being compared to a stopwatch recording . additionally , resting hr during a 3-min relaxation period prior to the interoception task was measured and then compared with participants estimate of their resting hr to index hr belief accuracy ( calculated in the same way as heart and time estimation accuracy ) . if the time approximation strategy is confounding results , any relationship between interoceptive accuracy and ug behavioral and physiological measures should no longer hold when covarying out these variables . age , gender , body mass index ( bmi ) , resting hr , iq , and physical activity ( assessed using the scale described by ehlers & breuer , 1992 ) have also previously been associated with heartbeat perception accuracy , so these details were additionally measured and entered as covariates . interoception accuracy , time accuracy ( on a trial - by - trial basis ) , and hr belief accuracy were expressed as percentage error scores . following the standard approach in the literature , these were calculated by taking the modulus of the actual value minus the estimated value , dividing this by the actual value , and then multiplying by 100 ( [ actual  estimatedactual ]  100 ) ( see ehlers & breuer , 1992 ) . modulus scores were used as the primary index of accuracy ; the distribution of nonmodulus scores is very difficult to interpret , because very negative and very positive values would both indicate poor accuracy . in practice , nearly all participants underestimated their hrs in the present sample , meaning that the modulus and nonmodulus scores were extremely similar ( r = .98 , p < .001 ) . we selected the mental tracking task ( schandry , 1981 ) rather than alternative tone detection procedures ( e.g. , whitehead , drescher , heiman , & blackwell , 1977 ) to measure heartbeat perception since , when piloting the latter in our laboratory , we found they were not a particularly sensitive individual differences measure . specifically , a large proportion of participants performed at chance levels , consistent with the relatively low rates ( 4050  % classified as perceivers ) of detection typically found in the literature ( e.g. , eichler & katkin , 1994 ; knapp - kline & kline , 2005 ) , introducing a floor effect into the data and reducing the sensitivity of the task as an individual differences measure . there is no clear superiority for either task in terms of how well they deal with possible interpretation confounds ( knapp - kline & kline , 2005 ) or how widely they are used in the literature ( see dunn et al . , 2010a , 2010b supplementary materials ) . given that the primary focus of the present study was on individual differences , we therefore selected the schandry task . eda ( in microsiemens ; s ) and hr ( in beats per minute ; bpm ) responses when receiving each offer were recorded using a biopac mp100 system ( biopac , 1997 ) acquiring data at 1,000 samples per second . we conceptualized these parameters as measures of core affect rather than discrete emotions ( cf . , 2004 ; dunn et al . , 2010a , 2010b , study 2 ) , with eda particularly relating to sympathetic nervous system modulation of arousal / activation and hr as particularly relating to joint sympathetic and parasympathetic modulation of valence ( e.g. , bradley , codispoti , cuthbert , & lang , 2001 ) . eda was recorded using two grounded ag  agcl electrodes ( biopac tsd203 transducer ) that were secured ventrally on the distal index and middle finger of the nondominant hand , with biopac eda paste ( with a nacl concentration of 0.05  m ) as the electrolyte . agcl ecg electrodes were placed on the dorsal forearms with clip - on shielded leads attached for hr recording . hr responses were quantified as mean hr change during the offer period , relative to a pre - offer 1-s baseline . eda responses were quantified as the maximum positive change observed during the 6-s offer period , excluding trials where no positive change occurred ( i.e. , amplitude ; cf . pollatos , schub , herbert , matthias , & schandry , 2008).2 we computed the median value of eda and hr response to each offer type and additionally natural log transformed the eda variables , prior to analysis to minimize outlier effects . since the eda analysis did not use a baseline subtraction to control for variation in background activity , we covaried mean eda across the entire ug in all individual differences analyses . we also recorded hr variability during a 5-min baseline recording taken prior to the ug as an additional measure of trait emotion regulation . r intervals for each participant was visually inspected for marked outliers . where outliers were identified , the raw ecg data was reexamined and adjusted if necessary . hrv was then indexed using cmetx software ( allen , chambers , & towers , 2007 ) . we analyzed log hrv as a measure of overall hrv , the cardic vagal index ( cvi ) as a measure of vagal ( parasympathetic ) contribution to hrv , and the cardiac sympathetic index ( csi ) as a measure of sympathetic contribution to hrv . figure  1 plots rejection percentage , fairness ratings , and anger ratings for each offer type . showing that the task was working as intended , participants rejected more unfair than fair offers , f(1 , 50 ) = 139.05 , p < .001 , and tended to reject more human than computer offers , f(1 , 50 ) = 3.21 , p = .08 . there was an interaction between fairness and proposer type , f(1 , 50 ) = 5.23 , p = .03 , with participants rejecting more unfair offers from human proposers than computer proposers , t(50 ) = 2.13 , p = .04 , but not differing in their rejections of fair human or computer offers , t < 1 . the use of anova approaches with proportion data has been criticized , and alternative multilevel logistic regression techniques have been recommended ( jaeger , 2008 ) . multilevel analyses consider effects at the individual trial level , taking into account that each trial is nested within a particular participant . we repeated the key rejection rate analysis using multilevel logistical regression ( applying the xtmelogit command in stata 11.0 ; statacorp , 2009 ) . rejection rates were greater for unfair than for fair , b = 5.08 , se = 0.61 , z = 8.32 , p < .001 , and for human than for computer , b = .65 , se = .22 , z = 2.97 , p < .01 , offers . however , in contrast with the anova analyses , there was no significant interaction between fairness and proposer , b = 1.28 , se = .84 , z = 1.52 , p = 0.13.fig . 1percentage of offers rejected , anger ratings and fairness ratings for each offer type . anger and fairness ratings on scales from 0 ( not at all ) to 100 ( extremely ) . data are mean ( standard error of the mean ) values percentage of offers rejected , anger ratings and fairness ratings for each offer type . anger and fairness ratings on scales from 0 ( not at all ) to 100 ( extremely ) . data are mean ( standard error of the mean ) values more anger was experienced to unfair than to fair offers , f(1 , 50 ) = 62.86 , p < .001 , and to human than to computer offers , f(1 , 50 ) = 10.04 , p < .04 , and again there was an interaction between fairness and proposer , f(1 , 50 ) = 10.91 , p < .01 . participants felt more angry to unfair human offers than to unfair computer offers , t(50 ) = 3.24 , p < .01 , but did not differ for human and computer fair offers , t < 1 . participants rated unfair offers as less fair than fair offers , f(1 , 50 ) = 424.51 , p < .001 . although there was no overall difference between fairness ratings of human and computer proposals , f < 1 , there was an interaction between fairness and proposer , f(1 , 50 ) = 10.99 , p < .01 . participants reported that human unfair offers were less fair than computer unfair offers , t(50 ) = 2.65 , p = .01 , but that human fair offers were more fair than computer fair offers , t(50 ) = 3.09 , p < .01 . since anger and fairness ratings were taken retrospectively rather than after each offer , it was not possible to conduct multilevel analyses . we subsequently focus on rejection rates , but for further analysis of the anger and fairness responses see the supplementary material . there was a greater eda response to rejected than to accepted offers , f(1 , 31 ) = 14.19 , p = .001 , but there was no main or interaction effect of proposer , fs < 1 ( see fig . comparable analyses were conducted on the hr data , excluding two outliers with significant movement artefact in their recording trace . there were no main effects of proposer or decision , fs < 1 , and the interaction was nonsignificant , f(1,31 ) = 1.75 , p = .20 ( see fig . 2eda ( a ) and hr ( b ) responses to different offer types on the ug . data are mean ( standard error of the mean ) values eda ( a ) and hr ( b ) responses to different offer types on the ug . data are mean ( standard error of the mean ) values because there were no significant proposer effects and we had no a priori hypotheses regarding differential bodily responses as a function of proposer , for subsequent analyses , we collapsed across human and computer offers to increase the sample size available to analysis . offers that were rejected continued to produce a greater response than those that were accepted in terms of eda , t(44 ) = 2.95 , p < .01 , but not hr , t(44 ) = 1.63 , p = .11 . next , we examined whether individual differences in bodily responses predicted ug rejection behavior . we subtracted eda / hr responses to accepted from rejected offers , with a larger value on this differentiation index indicating a greater response to rejected , relative to accepted , offers . there was no significant relationship between overall rejection rates and eda differentiation ( covarying for mean eda level ) , rp = .01 , p = .72 , or hr differentiation , r = .22 , p = .15 . of the 45 individuals with eda responses to both accepted and rejected offers , one had incomplete interoception data , and three had incomplete rest data because of experimenter error , leaving a sample of 41 available for analysis . there was a good spread of interoceptive ability across the sample ( mean error score = 26.51  % , sd = 13.61 , range = 1.5657.65 ) . in zero - order correlations , interoception error was not significantly related to overall rejection rates , eda differentiation , or hr differentiation , ps > .17 . however , interoception error was trend related to reduced anger , r = .25 , p = .09 , and was significantly related to less unfair fairness , r = .34 , p = .02 , ratings of unfair ( relative to fair ) offers . in other words , as individuals interoceptive abilities improved they showed a greater anger response to unfair offers and experienced inequitable offers as more unfair . to examine whether interoception moderated any relationships between ug behavior and bodily responses ( hypothesis 2 ) , we entered interoception error , eda differentiation , and mean eda during the ug ( all z - scored ) . at the second step , we entered the product term of the interoception error and eda differentiation variables ( aiken & west , 1991 ; baron & kenny , 1986 ) . significant moderation is indicated by the fit of the model improving from step one to step two . comparable analyses were conducted for hr differentiation , except that mean hr during the ug was not included as an additional covariate . we examined each of these analyses for the presence of multivariate outliers using mahalanobis distance . following tabachnik and fidell ( 2001 ) , we identified the  value that would be significant at the p < .001 level for analyses with degrees of freedom equal to the number of independent variables ( four for eda ; three for hr ) . three outliers were excluded on this basis , leaving a final sample size of 38 . in the eda analyses , a significant moderating role of interoception was observed , f(1 , 33 ) = 7.05 , p = .01 , r = .15 , r total = .28 . figure  3 plots this interaction using the method of simple slopes ( aiken & west , 1991 ; see dunn et al . consistent with hypothesis 2 , greater eda differentiation predicted higher rejection rates in those with better interoception , whereas there was no clear relationship between rejection levels and eda response in those with poorer interoception . the interaction remained significant if ranking data prior to the analysis ( conover & iman , 1981 ) to further minimize outlier effects , f(1 , 35 ) = 8.38 , p < .01 , r = .18 , r total = .29 . the interaction also held if additionally controlling for all of the possible nuisance variables that have been linked to interoceptive awareness in previous research ( entering age , gender , estimated iq , physical activity , time estimation error , hr belief accuracy , and bmi at step one of the regression ) , f(1 , 23 ) = 14.38 , p < .001 , r = .21 , r total = .66 . this suggests that performance on the cardiac perception task is genuinely measuring interoceptive awareness and is not acting simply as a proxy for other variables such as age , iq , and so on . in hr analyses ( excluding two multivariate outliers ) , there was no significant moderating role of interoception , f < the reported effects were unchanged when the rejection proportion variables were transformed using either arcsine or logit transformations following jaeger ( 2008).fig . 3the relationship between eda differentiation and the proportion of human offers rejected as a function of good , average , and poor interoceptive accuracy . more negative eda differentiation = 1 sd ; average eda differentiation = 0 sd ; more positive eda differentiation = + 1 sd . good interoception = 1 sd error score ; average interoception = 0 sd error score ; poor interoception = + 1 sd error score the relationship between eda differentiation and the proportion of human offers rejected as a function of good , average , and poor interoceptive accuracy . more negative eda differentiation = 1 sd ; average eda differentiation = 0 sd ; more positive eda differentiation = + 1 sd . good interoception = 1 sd error score ; average interoception = 0 sd error score ; poor interoception = + 1 sd error score five participants hrv data could not be corrected for movement artefact , leavening a sample of 46 participants for hrv analysis . consistent with hypothesis 3 , increasing hrv was related to total offers rejected for both log hrv , r = .35 , p = .02 , and the cardiac vagal index ( cvi ) , r = 37 , p = .01 , a measure of sympathetic contribution to hr regulation . there was no significant relationship with the csi , r = .13 , p = .38 . we also conducted exploratory analyses to establish whether interoceptive awareness moderated the link between hrv and ug responses . a trend significant moderating role of interoception was found on the relationship between log hrv and rejection rates , f(1 , 41 ) = 3.45 , p = .07 , r = .07 , r total = .20 ( see fig . greater hrv predicted lower rejection rates in those with worse interoception , but was unrelated to rejection rates in individuals with better interoception . this finding again held if additionally controlling for the nuisance variables previously related to cardiac perception performance ( entering age , gender , estimated iq , physical activity , time estimation error , hr belief accuracy , and bmi at step one of the regression ) . an identical pattern of findings emerged if using the cvi index of hrv , but no findings were significant if using the csi measure . this further indicates it is the vagal ( parasympathetic ) component of hrv that is largely accounting for these results.fig . 4the relationship between hrv and the proportion of human offers rejected as a function of good , average , and poor interoceptive accuracy . good interoception = 1 sd error score ; average interoception = 0 sd error score ; poor interoception = + 1 sd error score the relationship between hrv and the proportion of human offers rejected as a function of good , average , and poor interoceptive accuracy . good interoception = 1 sd error score ; average interoception = 0 sd error score ; poor interoception = + 1 sd error score rejection behavior on the ug has been understood as a failure of emotion regulation . here , we attempted to extend this account by examining whether the bodily component of emotional responses can account for individual variability in rejection rates ( see bodily feedback theories ; craig , 2009 ; damasio , 1994 ; james 1884 ) . showing that the ug functioned as expected in the present study , participants rejected more unfair offers , experienced greater anger to unfair offers , and rated them as less fair . this further indicates that rejection of unfair offers and the subjective responses to unfairness on the ug are robust phenomena . individuals exhibited a greater eda response to rejected , relative to accepted , offers , as predicted in hypothesis 1 . although rejection rates , anger ratings , and unfairness ratings were greater for human relative to computer offers , there was no significant difference in bodily responses as a function of proposer . this suggests that enhanced behavioral reaction to unfair human ( relative to computer ) proposals is not driven solely by bodily feedback mechanisms , and may instead reflect some other , as yet unspecified , mechanisms . that we observed some effects for eda but not hr parallels mixed results in the existing literature . ( 2009 ) found that eda differentiated between fair and unfair offers in healthy participants , osumi and ohira ( 2009 ) reported that hr but not eda related to offers that were rejected versus accepted . it is noteworthy that the present study has a larger sample than these earlier studies ( n = 51 as compared with n = 20 in osumi and ohira , 2009 ; n = 30 in vant wout et al . , 2006 ; and n = 14 in moretti et al . , 2009 ) , so our null hr results are unlikely to reflect lack of power . moroever , similar negative findings emerged when looking at initial hr deceleration , subsequent hr acceleration , and variability in hr response during the offer period , meaning this pattern of findings is not an artefact of the particular analysis strategy we adopted . changes in mean hr activity are difficult to unambiguously interpret in any case , because of the difficulty in disentangling sympathethic and parasympathetic contributions to hr control . our second ( and central ) hypothesis that interoceptive accuracy would moderate the relationship between bodily responses and rejection rates , was supported for eda data only . we found a significant moderating role of interoception on the relationship between eda responses and rejection rates of offers . those with accurate interoception showed a positive coupling between increased unfair rejection rates and greater eda responses to rejected , relative to accepted , offers . this association between bodily responses and rejection rates largely disappeared in those with inaccurate interoception . this is consistent with emotion regulation accounts of ug rejection behavior ( e.g. , sanfey et al . , 2003 ) , extending these by showing that embodied components of emotional reactions also drive responses to financial inequity . these results conceptually replicate our previous findings that interoception moderates the relationship between bodily responses and cognitive  affective processes ( dunn et al . , 2010a ) , this time in the social decision - making domain . this extends previous psychophysiological findings on the ug ( e.g. , vant wout et al . , 2006 ) by showing that it is the interplay between bodily responses and their perception that can best account for individual differences in rejection rates . it is unsurprising that no moderation effect emerged for the hr data , given that hr response did not differentiate between rejected versus accepted offers in the first place . the present data speak to the direction of the relationship between bodily changes and cognitive  affective processes observed in earlier studies . jamesian theories would directly predict that interoceptive accuracy will moderate the extent to which bodily responses shape how we think and feel ( e.g. , damasio , 1994 ; james , 1884 ; see dunn et al . however , accounts that view bodily responses solely as an epiphenomenom would not predict a priori a moderating role of interoception and struggle to account for this finding parsimoniously . in particular , if the body is nothing but a downstream consequence of a central brain - based response , then why would the accuracy with which an individual can monitor the body determine the degree of coupling between bodily responses and cognitive  affective processes ? for this reason , we feel that the present results are more easily explained by accounts suggesting bodily responses are at least partly causal rather than solely epiphenomenal . it was further observed that greater hrv ( particularly parasympathetic components ) was associated lower rejection rates across the sample , as predicted in hypothesis 3 . given that hrv is viewed as measure of dispositional emotion regulation capacity ( appelhans & leucken , 2006 ) , this further supports the hypothesis that rejection behavior on the ug relates to a failure in emotion regulation processes , as evidenced for example by increased rejection in patients with ventromedial prefrontal cortex damage ( koenigs & tranel , 2007 ) . in particular , vagal inhibitory mechanisms are seen as central in allowing individuals to flexibly adjust metabolic expenditure in rapidly changing social environments ( porges , 1995 ) . as the vagus exerts greater control on the heart , this reduces flight / fight behavior and instead promotes affiliative responses . acceptance of ug offers can be viewed as an example of such affiliative tendencies at the individual levels ( although see accounts arguing that rejection is a prosocial behavior at the societal level , since it punishes behavior that violates group norms ; fehr & fischbacher , 2003 ) . in exploratory analyses contrary to the state eda findings , there was a nonsignificant trend for greater hrv to become increasingly associated with lower rejection rates as interoceptive accuracy worsened . one way to interpret this pattern of findings is to propose that trait hrv and state eda have independent effects on the ug . in poor interoceptors , state eda changes have little impact because the individual can not accurately detect them , so ug decision making is more strongly influenced instead by trait hrv . in contrast , in accurate interoceptors , state eda has a large impact as the individual is sensitively attuned to them , so ug decision making is less clearly affected by trait hrv . again , this moderation relationship is difficult to explain with frameworks that argue that bodily responses are not causally involved in the decision - making process . as examining the interaction between hrv and interoception was not an a priori aim of this study and the moderation effect was only trend significant , these results require replication and should be interpreted cautiously at the present time . that eda primarily reflects sympathetic nervous system function , whereas the hrv effects are primarily parasympathetic in nature , is consistent with the notion that they will have independent effects on ug decision making . overall , these findings also suggest a possible reinterpretation of what insular activation found in previous fmri studies during the ug actually means . given that the anterior insular has been robustly implicated in interoception ( craig 2009 ; critchley et al . , 2004 ) , it is plausible that previous findings of insular activation on the ug might reflect the general representation of bodily responses ( see also kirk , downar and montague 2011 ) , as opposed to activation of distinct negative affective states such as disgust or anger ( sanfey et al . , 2003 ) . indeed , many functional imaging studies using appetitive tasks also detect anterior insula responses , particularly for monetary wins that are also physiologically arousing ( clark , crooks , clarke , aitken , & dunn , 2012 ; clark , lawrence , astley - jones , & gray , 2009 ; elliot , friston , & dolan , 2000 ) , indicating that the insular is not specific to negative emotions . in our view , the existing evidence is most consistent with the view that bodily signals provide a crude sense of emotional arousal ( i.e. , core affect ; barrett , 2006 ) , which needs to be appraised centrally to lead to clearly valenced emotions or discrete emotional states ( barrett et al . , 2004 ; dunn et al . this reinterpretation of insular function on the ug of course relies on reverse inference , and it would now be useful for a combined fmri and psychophysiology study to be run to test this account . it is important to be clear that we are not claiming that central brain - based mechanisms are not involved in social decision making . in particular , bodily responses have to be generated in the first place , presumably by some kind of activity in the brain . nor do our findings indicate that bodily responses are a necessary component of the mechanism underpinning ug rejection . in particular , those with poor interoception nevertheless rejected the same proportion of offers as those with accurate interoception . this further indicates there are individual differences in the degree to which embodiment mechanisms are implicated in cognitive  affective processing ( dunn et al . an important question to consider is whether the present findings have any implications for everyday decision making . as previously discussed , rejection behavior on the ug is  irrational  in the sense that it leads to personal financial loss ( cf . 2003 ) , but is  rational  in light of the potential benefits for the social groups in enforcing social norms ( cf . state increases in electrodermal reactivity to financial offers , and enhanced perception of these changes via interoceptive mechanisms , appear to lead to societal gain but personal cost ( i.e. greater rejection of unfair offers ) . trait regulation of the body via increased hrv arguably leads to personal gain but brings costs to the group ( i.e. reduced rejection of unfair offers ) . it is possible that a range of training techniques could develop this flexibility and therefore promote adaptive social decision making . for example , helping individuals to regulate hrv could allow them to decide if they wish to reduce  rejection behavior by increasing vagal control or increase  rejection behavior  by relinquishing vagal control . moreover , training the capacity to modify interoception , perhaps by use of neurofeedback of right anterior insular activity ( e.g. , caria et al . , 2007 ) , could enable individuals to tune in or out of bodily signals as required . finally , regular bodily focused meditation practices ( sze , gyurak , yuan , & levenson , 2010 ) could change the coupling seen between bodily responses and subsequent rejection behavior . in particular , the observing , nonjudgmental relationship to the body that mindfulness cultivates may facilitate more reflective and less impulsive reactions to consistent with this possibility , expert meditators have been found to activate the posterior rather than anterior insular when performing the ug ( kirk et al . , 2011 ) , and it has been argued that this shift accounts for their decreased rejection rates of unfair offers . of course , these intervention ideas are speculative at the present time and require empirical validation . there are a number of limitations of the present study that need to be held in mind . we chose the schandry task because it is viewed as a general index of interoceptive awareness and has been most closely linked to cognitive  affective processes ( see dunn et al . , 2010a ) . nevertheless , it is possible that noise has been introduced into the present data set by measuring interoception in the cardiac domain and relating this to bodily responses to the ug in the electrodermal domain . by incorporating multiple measures of bodily response and perception this potential source of error can be minimized in future work . second , we indexed only eda and hr . although this is appropriate given the present focus on arousal , it is not sufficient to make strong claims about whether or not bodily responses lead to distinct emotions such as anger and disgust ( cf . third , although a robust measure of social decision making , the ug is nevertheless of questionable ecological validity . it would now be interesting to see whether comparable results emerge in more real - world contexts . fourth , although the interplay between bodily responses , their perception , and their regulation did account for significant individual variation in rejection rates , a large amount of the variance in the model nevertheless remained unexplained . this suggests other additional factors need to be examined ( e.g. , individual differences in social altruism or trait affect ; see dunn et al . fifth , the moderation approach adopted here , although suggestive of the direction of the relationship between body and mind , does not provide conclusive causal support for bodily feedback theories . in particular , an alternative explanation of the interaction effects is that bodily responses moderate the response between rejection rates and interoception . to definitively establish the causal role of bodily feedback mechanisms , sixth , we utilized retrospective anger and fairness ratings of the offers , because we did not want these judgments to bias , reject , or accept decisions . the present data further support the notion that emotion regulation mechanisms relate to rejection behavior on the ug . our results suggest that  gut feelings  arising from the body , interacting with the ability to accurately perceive bodily feedback , partly shape social decision making . furthermore , superior capacity to regulate bodily responses via vagal inhibition ( indexed in terms of hrv ) also influences the degree to which individuals respond emotionally on the ug . this interplay between bodily response , regulation and perception can therefore account for individual differences in how we react to perceived unfairness .
it has been robustly demonstrated using the ultimatum game ( ug ) that individuals frequently reject unfair financial offers even if this results in a personal cost . 
 one influential hypothesis for these rejections is that they reflect an emotional reaction to unfairness that overrides purely economic decision processes . in the present study 
 , we examined whether the interplay between bodily responses , bodily regulation , and bodily perception (  interoception  ) contributes to emotionally driven rejection behavior on the ug . 
 offering support for bodily feedback theories , interoceptive accuracy moderated the relationship between changes in electrodermal activity to proposals and the behavioral rejection of such offers . 
 larger electrodermal responses to rejected relative to accepted offers predicted greater rejection in those with accurate interoception but were unrelated to rejection in those with poor interoception . 
 although cardiovascular responses during the offer period were unrelated to rejection rates , greater resting heart rate variability ( linked to trait emotion regulation capacity ) predicted reduced rejection rates of offers . 
 these findings help clarify individual differences in reactions to perceived unfairness , support previous emotion regulation deficit accounts of rejection behavior , and suggest that the perception and regulation of bodily based emotional biasing signals (  gut feelings  ) partly shape financial decision making on the ug .