In this study, we investigated cooperative behaviour in kidney donor and transplant candidates using a standard moral dilemma task, the Prisoner’s Dilemma (PD). The current study extends past research by implementing a computerized PD game in which participants who are either kidney donor or transplant candidates play a number of PD iterations with the computer as their partner. Τhe computer was programmed to follow different strategies which were more or less cooperative or conflicting. We analyzed reaction times and degree of cooperation following reward vs. punishment in kidney donor and transplant candidates. We answer our research questions by demonstrating the following key findings: 1) Confirming the effect of the partner’s intention, participants’ degree of cooperation was modulated based on the strategy of the computer (higher/lower cooperation for more reciprocative/conflicting strategies), and was higher following reward than punishment; 2) There was a trend for donors to be faster than recipients, while in both groups reaction times following reward and punishment were correlated; and 3) Recipients responded equally strongly to reward and punishment as the higher the cooperation following reward, the lower the cooperation following punishment, which was also reflected in faster (slower) reaction times for reward (punishment), whereas donors did not show correlations between cooperation to reward and punishment. Overall, our findings contribute to the investigation of the psychological and cognitive features of kidney donors.
As expected, participants’ degree of cooperation was modulated based on the strategy of the computer, namely both kidney donor and transplant candidates similarly cooperated less during selfish behaviour. More specifically, we observed higher degree of cooperation for more reciprocative strategies, i.e. pavlov, always cooperate, tit-for-tat, whereas there was lower cooperation for conflicting strategies, i.e. pavlov random, always defect. This indicates that participants’ willingness to cooperate with others changes as a function of the nature of their relationships, namely selfish treatment triggered retaliation. Previous studies have showed that older adults tend to handle emotion regulation in interpersonal conflict passively [28, 29] and behave assertively in situations that elicit anger or annoyance [29]. The age distribution of our sample was above the younger adults who are usually considered until 25 years old. Therefore, our finding is in line with previous work showing that people, independently of their age, tend to adjust their cooperation levels based on the behaviour of their partner [30]. Additionally, this is further corroborated by our other finding that cooperation degree was higher following reward compared to punishment. In particular, this provides evidence for two points: 1) the measures of “reward” and “punishment” that we constructed indeed represented the perception of participants and thus affected their subsequent decisions; and 2) it confirms the observation that cooperation is modulated by the perceived intention of the partner’s reciprocative or selfish behaviour [23]. Our aforementioned findings did not significantly differ between groups, suggesting that cooperative performance in the PD is not affected by the process of kidney donation or receival. Future studies are needed to investigate whether kidney donor and transplant candidates are differentiated in other aspects of morally-laden behaviour, potentially using a different kind of task.
Furthermore, there was a trend for donors to be faster than recipients, which was however not statistically significant. First, it is possible that this did not reach significance due to the low sample size in our study. Further studies employing a larger sample size are needed to test this possibility. One explanation could lie on possible cognitive impairments of transplant candidates compared to kidney donors [31]. Indeed, cognitive impairment is common in patients undergoing hemodialysis [32]. The most affected domains are executive functions and speed of processing [33]. Another speculation could lie in an overall tendency of transplant candidates to be more suspicious and show less trust with regard to the motives of other individuals, which might have led them to take more time to make a decision that taps onto mutual trust and the relationship between the partners [34]. Additionally, we observed that in both groups reaction times following reward and punishment were correlated. This indicates that decision speed was not differentiated at the level of perceived reward or punishment by the other player/computer.
Interestingly, transplant recipients’ behaviour was correlated between reward and punishment: the higher the degree of cooperation following reward, the lower the degree of cooperation following punishment. Furthermore, the more recipients cooperated following reward, the faster they responded, while the more they cooperated following punishment, the slower they responded. The transplant candidates’ hesitancy to cooperate after punishment may be due to their increased sense of vulnerability [35–37], leading to a higher level of depression and concerned stance (e.g. somatic concerns) compared to kidney donor candidates [38]. In this view, recipients’ hesitancy to proceed with an altruistic choice lies on hesitancy to proceed with a course of action that will increase their vulnerability. On the contrary, kidney donors did not show correlations neither between the degree of cooperation following reward and punishment nor between the degree of cooperation and reaction times. We will provide alternative explanations for these results. First, it seems like transplant recipients might have a strong preference for reward together with a strong dislike for punishment. In addition, the observation that transplant recipients cooperated faster after reward, whereas they cooperated slower after punishment, indicates that it took more time for them to cooperate after punishment. This delay might be related to being less inclined to cooperate after punishment. Nevertheless, previous studies investigating decision-making in moral dilemmas have assumed that players think less to make intuitive decisions and longer to make deliberate decisions, and thus concluded that the type of decisions with smaller reaction times are intuitive and those with the longer reaction times are deliberate [39–41].
The absence of the aforementioned effects for kidney donor candidates shows that they were more decided to cooperate independently of whether their partner/computer rewarded or punished them. This is in line with the notion that organ donation resembles gift giving via the voluntary will to help someone for altruistic reasons [7, 8, 11]. It is also interesting to highlight that numerous studies have shown that most organ donors make an instantaneous decision to donate with little or no deliberation and have no regrets about doing so [42, 43]. Another relevant point here refers to the personality characteristics of kidney donor candidates. Kidney donors have been observed to be higher in agreeableness and lower in neuroticism compared to the general population [44, 45]. Agreeableness includes cooperativeness and a prosocial, forgiving orientation, while low neuroticism is linked to emotional stability and low vulnerability to stress. People with these characteristics might be more willing to donate, as agreeableness and neuroticism play an important role in social contexts [44]. Another possibility could be that donors’ altruistic behaviour was a reflection of social desirability, which potentially underlines their decision for organ donation [46, 47]. Therefore, our findings provide evidence that donors are more decisive during decision-making on dilemmas with regard to cooperation vs. competition, whereas recipients show a dependence on their partner’s behaviour, as they cooperate more when their partner rewards them, but cooperate less when their partner punishes them. Future studies are needed to directly investigate potential associations between personality and cooperation in the prisoner’s dilemma in organ donors and recipients. Overall, we believe that our findings shed light on the psychological and cognitive characteristics of kidney donors, which is fundamental to the optimization of their psycho-social management and support [48–50]. Crucially, this issue has clear moral implications linked to the principles of autonomy and justice [51].
Our study is not without limitations. First, biological sex was not balanced between groups, with the majority of donors being females whereas recipients being mostly males. Indeed, previous work has revealed a gender disparity in living renal transplant donation, namely that the vast majority of donors are females, which might be related to social desirability stemming from societal pressure [9, 52], although not all research converges to this hypothesis [53]. Second, our sample size was limited which means we might have not have been able to detect smaller effect sizes. Third, a healthy group not involved in the kidney transplant procedure would be necessary to serve as a control, in order to test whether the effects identified in the kidney donor and transplant candidates would also be present in a sample of healthy adults. This would be especially useful for strengthening the findings on differences between groups with regard to reward and punishment.