在無知之幕後方的公平概念-台灣獼猴行為實驗

Abstract

公平一直是人類決策研究中一個重要議題。在過去研究中，影響最深遠的理論就是由美國哲學家John Rawls所提出無知之幕的概念(Rawls.1971)。在無知之幕後方的社會分配者，不知道自己在無知之幕揭開後，會是社會上的哪一個階層，所以決策者必須考量到所有階層狀況，此時決策者所做的分配就是該決策者的“公平概念”。 經濟學研究發現，在兩個期望值相同但風險不同的選項中，如果人類決策者只考慮自己的報酬時，通常會選擇風險較小的選項。但如果決策者的決定會影響他人時，決策者多會選擇利他的選項，顯示人類有正向的社會偏好。如果人類在無知之幕後方的選擇只考量報酬，不在乎其他人，則無知之幕後方的選擇就會等同風險偏好。Schildberg-Hörisch (2010)在人類身上重現無知之幕的實驗，分別測量受試者在風險情境、社會情境、還有無知之幕後方情境的決策行為，結果發現在無知之幕後方的受試者，選擇風險的比例顯著的少於在風險情境下選擇風險的比例，而女性減少的比例又大於男性。 本實驗使用台灣獼猴（Macaca cyclopis）當受試者，分別測試獼猴在社會情境、風險情境、無知之幕情境中的決策偏好。我們比較這三個情境的關聯性及差異，同時透過行為記錄確認動物彼此之間的社會關係，以及其對決策的影響。結果我們發現獼猴的決策與人類不同，猴子都是風險愛好者。但即使是風險愛好者，無知之幕後方選擇風險(不平等選項)的比例也明顯低於風險情境中選擇風險(不平等選項)的比例。這些結果顯示另外一隻猴子的存在，會降低選擇不平等選項的比例。

The veil of ignorance (VOI), behind which people allocate resource prior to learning their social positions, was introduced by John Rawls (1971). In a world of two, a prince and a beggar, an equal distribution yields an even share of resource to them, whereas an unequal distribution gives the prince the majority and leaves little for the beggar, preference over distributions may depend on a decision maker’s roles as a prince or a beggar. Decisions made before learning his roles are immune from being affected by his respective social position, and hence reflect what truly constitutes a just distribution. These are termed as preferences behind VOI, and they are therefore divided into two parts: the decision maker’s inequity aversion and their risk preference. In other words, when making decisions behind VOI, they balance between the desired distribution and the risk of not obtaining the desired role. We study the behavior of non-human primate, Formosan Rock Macaque (Macaca cyclopis), in the face of food decision problems. We conduct a class of modified dictator games in which a proposer chooses between two food allocations, and measure subjects’ preferences, including risk preference, inequity aversion, and preference behind VOI. Our data shows that subjects are strongly risk-loving and exhibit inequity aversion. Also, social context did affect choice in hierarchy system.