Edited by: Colin G. DeYoung, University of Minnesota, USA
Reviewed by: Alexander Weiss, The University of Edinburgh, UK; Raymond A. Mar, York University, Canada
*Correspondence: Stefan Sütterlin, Integrative Research Unit on Social and Individual Development (INSIDE), Campus Walferdange, Route de Diekirch, L-7220 Walferdange, Luxembourg. e-mail:
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The processes underlying decision-making in response to unfair offers in the ultimatum game (UG) have recently been discussed in light of models of reciprocity and fairness-related behavior. It has been suggested that behavior following norm-oriented, internalized expectations of reciprocity requires overcoming economic self-interest. In this study we investigated both, behavioral and peripheral-physiological indicators of inhibitory capacity related to neuronal networks that are likely to be involved in the behavioral response to unfair offers. Both heart-rate variability as an index of inhibitory capacity, and performance in a motor response inhibition task predicted rejection of unfair offers in an UG, suggesting an important role of inhibitory processes in overcoming economic temptations and regulating behavior conforming to social norms of reciprocity and fairness. The role of parasympathetic activity as a physiological trait-marker predicting inter-individual differences in the rejection of unfair offers is discussed.
Behavioral economics has traditionally ignored “irrational” decision-making as a concept as its models are mainly rooted in game theory, which conceptualizes humans as rationally acting individuals. Only recently, the importance of emotions on decision-making has begun to be acknowledged (Camerer,
Beyond the investigation of general psychological processes in neuroeconomics, an increasing number of studies have started to investigate individual differences in personality factors affecting behavioral tendencies observed in the UG, and their psychophysiological correlates. The majority of studies on inter-individual differences in the UG has concentrated on emotional processing such as appraisal and response strategies in response to unfair offers (Kirk et al.,
Neuroimaging studies have provided insight into the neural processes determining decision outcomes in the UG. Sanfey et al. (
The question remains, however, whether basic inhibitory processes are indeed involved in overcoming selfish action tendencies in the UG and if inhibitory processes and their consequences on decision-making behavior in the UG can be investigated by measures other than brain imaging methods. In the present study we applied two established measures of inhibitory capacity: motor response inhibition and cardiac-vagal control. Both measures are considered reliable measures of inhibitory capacity (Li et al.,
Heart-rate variability is a reliable, non-invasive measure of prefrontal inhibitory control and self-regulation. It is mediated parasympathetically (vagally) and obtained via electrocardiographic recording during rest (Segerstrom and Solberg Nes,
The central autonomic network model (CAN; Benarroch,
In summary, activation in prefrontal areas is known to be closely linked to inhibitory capacity and has been shown to be positively related to the rejection of unfair offers in the UG. These findings have been interpreted as reflecting top-down control of economic self-interest for the sake of fairness and reciprocity (Knoch and Fehr,
By applying physiological and behavioral trait measures of inhibitory control and quantifying their association with rejection frequency in the UG, this study is the first to compare self-regulatory capacity with responses to unfair offers by introducing HRV as a peripheral-physiological index for inhibitory control in decision-making in the UG.
Thirty-five adults were recruited from the undergraduate student population of the University of Würzburg and outside the University via advertisements. Seven volunteers from the student sample were familiar with the UG and, therefore, were not included in the dataset. Out of the remaining 28 adults (18 women) 21 were undergraduate students and seven from outside the University. Participant's age ranged from 18 to 34 years (
For the assessment of motor response inhibition we used the stop-signal task (SST, Logan et al.,
Electrocardiogram (ECG) was recorded using the Einthoven lead I configuration with disposable electrodes attached to the left and right wrists. Participants were instructed to relax and close their eyes while ECG monitoring for a period of 10 min. ECG raw data were recorded using a g. USBamp amplifier (sampling rate 500 Hz; g.tec, Graz, Austria).
In an effort to disguise the real purpose of the experiment participants were asked upon arrival at the laboratory to step in for another participant to support a research project on negotiations with students of economical sciences, just before the “actual” experiment he/she had signed up for was due to begin. The participant's role was described as the “assisting” counterpart in an experimental setting, in which the focus of the observation was on the other person, who was placed in an adjacent room. Room signs and temporary absence of the experimenter increased the credibility of the (fictitious) partner. The basic rules of the UG – i.e., options and their consequences – were explained. The experimenter left the room to collect the other (fictitious) participant's offer in a closed envelope, in which the offered ratio was marked on a prepared sheet. Not transparent for the actual participant, all offers started with a fair offer of 50:50 Cent, followed by eight subsequent offers, out of which the four ratios 60:40, 70:30, 80:20, and 90:10 were each chosen twice in randomized order. The randomization procedure was intended to minimize carry-over effects of ratio-sequences and potential assumptions on causal relations and expectations by the participant. After confrontation with the offer, the responder (participant) replied by marking the corresponding answer (“REJECT” vs. “ACCEPT”) underneath the offer on the prepared sheet, enclosed the sheet in the envelope with which the experimenter left the room and pretended to bring the participant's offer to the fictitious co-player. Instead of a computer program, a (fictitious) human co-player was chosen to increase the social relevance of the task and to ensure participants involvement in the task with sufficient associated emotional intensity (see Wout et al.,
After completion of the UG, the physiological assessment and the SST were carried out after a recovery break of 15 min before participants were debriefed and manipulation and credibility checks were completed.
Perceived anger and perceived unfairness were rated on visual analog scales for each ratio after completion of the UG to avoid systematic biases and reflections on the study's purpose during UG performance. Scales were presented with anchors “very fair”/“very unfair” and “I felt not angry at all”/“I felt very angry,” respectively. Subsequently, participants were debriefed and asked whether they were familiar with the UG or had previously taken part in a similar study.
Go-signal reaction time, stop-signal reaction time (SSRT) and percentage of correctly inhibited reactions in STOP-trials were calculated following the recommendations made by Logan (Logan and Cowan,
Offline analyses included the extraction of QRS complexes and interbeat intervals (IBI) from ECG recordings. Artifacts were detected via an individually calculated distribution-related threshold criterion (Berntson et al.,
Sex differences in the count of rejected offers (CRO), motor inhibition, and HRV were tested by independent samples
Self-report measures of perceived unfairness and experienced anger increased with offers becoming progressively unfair, indicating a negative association between reciprocity and emotional impact (Figure
Seven participants were familiar with the UG, although none of them had taken part in an UG before. All seven individuals were excluded from data analysis.
Correlation analyses between CRO and time domain measures of vagally mediated HRV measures of inhibitory control (RMSSD, pNN50) revealed significant positive associations of medium effect size (Figure
Mean reaction time to GO-trials was 433 ms (SD = 51 ms). Inhibitory control as indexed by percentage of successfully inhibited motor reactions in the SST showed the expected positive correlation with CRO (Figure
The intercorrelation between both measures of inhibition (HRV, SST) was not significant and for no HRV parameter higher than
Previous studies have shown that the control of economic temptation and behavioral regulation in the context of conformity with norms of fairness and reciprocity in the UG requires executive functions and the ability to inhibit pre-potent responses (Sanfey et al.,
The current results used HRV as a peripheral-physiological measure of inhibitory control that is presumed to be mediated by frontal cortical networks. The findings are in line with previous findings using neuroimaging (Sanfey et al.,
In the present study, indicators of inhibitory control predicted decision-making outcomes in the UG. Further research is needed to explore the nature of the association between inhibition-linked self-control and UG outcome. It may be surprising that the target of inhibition is economic self-interest, and not aversive emotions such as anger experience to an unfair offer. Rather, the results from the present study suggest that “rational” decision-making is not equal to “economic” decision-making, but reflects “economic management of one's emotional costs” in a given situation, requiring emotion regulation processes associated with inhibitory functions. Thus, emotional costs are an outcome of the unfair offer, but they also result from the (anticipated) experience of material loss and a violation of norms of reciprocity. They, therefore, must be overcome where economic self-interest is at stake. After all, economic interests and overcoming selfishness can be considered psychological costs due to the resulting experience of a loss. Thus, the rejection of an unfair offer, i.e., not receiving any payment at all, is at odds with the usually dominant goal of loss aversion (Kahneman and Tversky,
The present study used only two examples of inhibition paradigms. A broader range of inhibition measures (e.g., anti-saccades, inhibitory event-related potentials obtained by EEG) and experimental variations of conflicting interests such as using high vs. low monetary incentives (variation of economic incentives) would in future studies allow further conclusions regarding the role of subjective factors in the UG and the time course of inhibitory processes in decision-making. The association of inhibitory measures and rejection frequency should be less pronounced where overcoming anticipated psychological costs is required, compared to overcoming of economic interests, as postulated by previous research. Secondly, although we focused on inhibitory processes under resting conditions rather than autonomic reactivity
To our knowledge, this study is the first to demonstrate the effects of cardiac parasympathetic activity at rest as a physiological indicator of decision-making on responses to unfair offers. HRV and motor response inhibition are two established markers of inhibitory capacity; when combined they explained 36.5% of the variance of individual's UG rejection rate, suggesting a crucial role of individual self-regulatory capacity when responding to unfair offers. Our findings support Knoch et al. (
The current findings demonstrate the predictive power of physiological indicators of inhibitory capacity on UG outcomes. It further supports previous imaging findings suggesting an active inhibitory process in favor of fairness-related behavior and reciprocity.
In general terms, these findings suggest that physiological personality traits of inhibitory capacity like HRV can contribute to a better understanding of behavioral patterns in economic paradigms. This approach goes beyond the description of emotional responses triggered by external events and explains behavioral variance by objective assessment of physiological correlates of decision-making tendencies. Furthermore, future experimental approaches applying purely event-related physiological measures (e.g., phasic cardiovascular responses) to monitor processes in the UG such as arousal (i.e., emotional responsiveness to unfair offers) might benefit from additional assessment of variables with trait-characteristics to provide a broader picture of the determinants of behavioral outcome.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Mean | SD | CI | |||
---|---|---|---|---|---|
RMSSD | 44.84 | 13.92 | 0.426* | <0.05 | 0.09–0.81 |
pNN50 | 24.88 | 14.00 | 0.436* | <0.05 | 0.09–0.81 |
HF (ms2) | 729 | 471 | 0.294 | 0.073 | 0.00–0.97 |
HF (n.u.) | 35.01 | 17.61 | 0.282 | 0.077 | 0.09–0.67 |
Correct inhibitions (%) | 71.7 | 15.6 | 0.496** | <0.01 | 0.16–0.83 |
SSRT | 166.9 | 33.4 | −0.485** | <0.01 | −0.78 to −0.07 |