State Dependent Valuation: The Effect of Deprivation on Risk Preferences

The internal state of an organism affects its choices. Previous studies in various non-human animals have demonstrated a complex, and in some cases non-monotonic, interaction between internal state and risk preferences. Our aim was to examine the systematic effects of deprivation on human decision-making across various reward types. Using both a non-parametric approach and a classical economic analysis, we asked whether the risk attitudes of human subjects towards money, food and water rewards would change as a function of their internal metabolic state. Our findings replicate some previous work suggesting that, on average, humans become more risk tolerant in their monetary decisions, as they get hungry. However, our specific approach allowed us to make two novel observations about the complex interaction between internal state and risk preferences. First, we found that the change in risk attitude induced by food deprivation is a general phenomenon, affecting attitudes towards both monetary and consumable rewards. But much more importantly, our data indicate that rather than each subject becoming more risk tolerant as previously hypothesized based on averaging across subjects, we found that as a population of human subjects becomes food deprived the heterogeneity of their risk attitudes collapses towards a fixed point. Thus subjects who show high-risk aversion while satiated shift towards moderate risk aversion when deprived but subjects who are risk tolerant become more risk averse. These findings demonstrate a more complicated interaction between internal state and risk preferences and raise some interesting implications for both day-to-day decisions and financial market structures.生物体的内部状态会影响其决策选择。此前针对多种非人类动物（non-human animals）的研究已证实，内部状态与风险偏好（risk preferences）之间存在复杂交互作用，在部分情形中甚至呈现非单调（non-monotonic）特性。本研究旨在考察匮乏状态对不同奖励类型下人类决策的系统性影响。本研究同时采用非参数方法（non-parametric approach）与经典经济学分析（classical economic analysis）手段，探究人类受试者针对金钱、食物与水奖励的风险态度是否会随其内部代谢状态（metabolic state）发生变化。本研究结果复现了部分前期研究结论：平均而言，人类在饥饿状态下的金钱决策会变得更具风险容忍（risk tolerant）倾向。但本研究的独特实验设计，使我们得以针对内部状态与风险偏好的复杂交互关系提出两项全新观测结论。其一，食物匮乏（food deprivation）引发的风险态度变化是一种普适性现象，会同时影响受试者对金钱与可消耗类奖励（consumable rewards）的风险偏好。但更为关键的是，我们的实验数据表明，并非如此前基于受试者群体平均结果所假设的那样——所有受试者都会变得更具风险容忍倾向，而是当受试者群体整体处于食物匮乏状态时，其风险偏好的异质性（heterogeneity）会收敛至一个固定点（fixed point）。换言之，饱腹状态下表现出高风险厌恶（risk averse）的受试者，在匮乏状态下会转向中度风险厌恶；而原本风险容忍度较高的受试者，则会变得更为厌恶风险。上述研究结果揭示了内部状态与风险偏好之间更为复杂的交互关系，并为日常决策与金融市场结构均带来了若干值得探讨的启示。