The computational and neural substrates of moral strategies in social decision-making

Jeroen M Van Baar,Luke J Chang,Alan G Sanfey

doi:10.1038/s41467-019-09161-6

Jeroen M Van Baar, Luke J Chang + Show 1 more

Open Access

https://doi.org/10.1038/s41467-019-09161-6

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Abstract

Individuals employ different moral principles to guide their social decision-making, thus expressing a specific ‘moral strategy’. Which computations characterize different moral strategies, and how might they be instantiated in the brain? Here, we tackle these questions in the context of decisions about reciprocity using a modified Trust Game. We show that different participants spontaneously and consistently employ different moral strategies. By mapping an integrative computational model of reciprocity decisions onto brain activity using inter-subject representational similarity analysis of fMRI data, we find markedly different neural substrates for the strategies of ‘guilt aversion’ and ‘inequity aversion’, even under conditions where the two strategies produce the same choices. We also identify a new strategy, ‘moral opportunism’, in which participants adaptively switch between guilt and inequity aversion, with a corresponding switch observed in their neural activation patterns. These findings provide a valuable view into understanding how different individuals may utilize different moral principles.

Highlights

Individuals employ different moral principles to guide their social decision-making, expressing a specific ‘moral strategy’
The Moral Strategy Model accurately described the different hypothesized moral strategies (Fig. 2b; Supplementary Figure 3), and captured task behavior significantly better than the unitary models of greed, guilt aversion, and inequity aversion, as determined by the Akaike Information Criterion (AIC): ΔAIC with respect to greed model = –229.33, p < 0.001; ΔAIC w.r.t. guilt aversion = –82.33, p < 0.001; ΔAIC w. r.t. inequity aversion = –11.24, p = 0.021 (Fig. 2c). These results match those obtained in a direct behavioral replication of this experiment (n = 102; see Methods), where model AIC was again lowest for the moral strategy model: ΔAIC w.r.t. greed = –220.36, p < 0.001; ΔAIC w.r.t. guilt aversion = –76.04, p < 0.001; ΔAIC w.r.t. inequity aversion = –13.39, p = 0.010 (Supplementary Figure 4A)
By leveraging the between-participant differences captured in the two-dimensional parameter space of this model, we mapped the psychological computations corresponding to guilt and inequity aversion to specific parts of the human brain

Summary

Introduction

Individuals employ different moral principles to guide their social decision-making, expressing a specific ‘moral strategy’. We identify a new strategy, ‘moral opportunism’, in which participants adaptively switch between guilt and inequity aversion, with a corresponding switch observed in their neural activation patterns. These findings provide a valuable view into understanding how different individuals may utilize different moral principles. Different individuals may employ different sets of such fundamental priorities, expressing different “moral strategies” Such a strategy likely shapes not just political decisions and behavior in everyday social interactions. To address these questions, we designed the Hidden Multiplier Trust Game (HMTG; Fig. 1), which can elicit behavioral differences in the decision to reciprocate trust as a function of an individual’s moral strategy. On 25% of trials (the ×6 multiplier) the Trustee has more tokens than the Investor believes, and on 25% of trials (×2) they possess fewer tokens than the Investor thinks

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