| 摘要: | 為了研究影響人類公平性感知的影響因素，我們分別在三個實驗中的第一階段創造出一金錢不平等的情境，並操弄金錢的來源以及大小來檢視受試者在不同情境下對於下一階段(第二階段)的金錢分配會有甚麼樣的行為與神經機制上的差異。實驗中，受試者在第一階段會被分別分派到運氣組（隨機抽球）或是努力組（拉霸測驗）。實驗一另再加上數學測驗組（判斷數字大小），並根據受試者表現來決定是成為贏家或是輸家。贏家可得一筆獎金，輸家則無。第二階段受試者再度面臨十一種不同類型但總額相同的金錢分配，受試者須對不同分配做出滿意度的評分。
實驗一的行為實驗結果顯示，在三種組別的贏家和輸家都對第二階段自己全拿的分配最滿意，並未受到前一階段不平等的影響。我們認為是因為受試者將第一階段和第二階段視為兩個獨立的實驗。因此在實驗二的第二階段，我們在實驗畫面上，放上第一階段的結果作為強調並將第二階段的五十元提高到兩百元的金額分配。實驗二的行為結果顯示贏家和輸家在分配偏好上有顯著的差異，贏家認為第二階段的獎金平分是最滿意的分配，但輸家則是認為第二階段的獎金要全拿才是最滿意的。然而獎金的來源並未造成組間的差異。
在實驗三的設計中，我們讓受試者在不更動作業內容的情況下，分別參與了努力和運氣的兩種情境，目的是希望受試者在參加了兩種情境後，會藉此互相比較。我們使用了實驗二的實驗設計並同時加入了核磁共振造影的紀錄。實驗結果顯示，行為上，贏家相較於實驗二變得更以自利原則做考量，與輸家皆以自己全拿為最滿意的分配。然而，若我們檢視所有分配組的變異數，會發現贏家在自己比較少的分配上會有顯著大於輸家的個體差異，部分贏家會在自己相較於輸家金錢較少的分配上給出正向的滿意度。此結果顯示部分贏家還是有公平性的考量但是人數上沒有較實驗二來的多。神經資料上，我們發現，即便受試者的滿意度有高有低，但這樣的行為卻沒有反應在過去文獻指出被認為是處理主觀價值的腹內側前額葉皮質和腹側紋狀體。不過，我們發現若將決策過程時的大腦反應和僅僅只是相同按鍵反應的過程相比較，頂葉皮層以及腦島有更顯著的活化反應。這樣的結果顯示了受試者正在處理酬賞資訊，不論該酬賞與對手相比是較多或是較少。另外，輸家腦島區域活化程度和其主觀評分之間的關聯也顯著的高於贏家，意味著輸家在第二階段明顯的比贏家在專注度和情緒上都更容易受到影響。
本研究結果指出，受試者與他人金錢差距的比較對受試者於公平感知以及後續金錢分配的滿意度有很重要的影響，然而即便環境中存在不同操弄受試者公平感知的因素，例如本實驗操弄的不平等來源以及差距，個體差異仍很大程度左右了這些因素對受試者公平性感知的效果。
;To investigate how the interfering factors affect people’s fairness perception, we experimentally manipulated the source of monetary reward that is determined by a luck-based or effort-based task and examined whether the allocation of the monetary reward would modulate participants’ satisfaction of monetary distribution. We conducted three experiments in total. Specifically, in the first stage of all the experiments, college students were classified as “winners” or “losers”, each of which was against one opponent, based on pure luck (i.e., random drawing) or real efforts (i.e., a number-line dissection task). In Experiment 1, we also included a math-ability task (i.e., ten arithmetic math questions). Winners across all conditions received all and the same amount of monetary reward, while losers received no reward. In the second stage of every experiment, all participants were asked to make satisfaction ratings for the distribution of an additional amount of monetary reward between themselves and the opponent.
Experiment 1 showed similar behavioral patterns of preferring the self-more distribution (i.e., participants received more money than the opponent) in the luck, the math, and the effort conditions for both winners and losers. Participants were not affected by the inequality in the first stage, possibly because the two experimental stages were perceived as independent. Therefore, in Experiment 2, we modified the total amount of the monetary reward of the distributions and emphasized the inequality between winners and losers in the second stage. The results showed that both in the luck and the effort conditions, winners preferred equal over unequal distribution of which they received more additional monetary reward than losers (i.e., the self-more distribution). Losers, in contrast, in both the luck and the effort conditions tended to prefer self-more over equal or self-less distribution of which participants received less money than the opponent. We did not observe the effect from the source of the reward in Experiment 2.
In Experiment 3, we adopted the design of Experiment 2 and changed the original between-subject design into within-subject design, that is, all participants experienced the luck and the effort conditions in combination with simultaneous fMRI recording. Behaviorally, the effect of the manipulations in the allocation of reward was weaker than that in Experiment 2, as both winners and losers preferred the self-more distribution. We did not find strong evidence for the effect of the source of the monetary reward. However, when examining the variance of rating for each distribution, we observed a larger individual difference among winners than among losers in Experiment 3. Some winners in Experiment 3 gave a positive rating even under the self-less distribution. This indicated that some winners still took fairness into consideration, yet the number of people was not as many as in Experiment 2. From our neural data, we did not find the brain areas that were identified to be involved in processing subjective value in previous literature, such as the ventral striatum and the ventromedial prefrontal cortex (vmPFC), to associate with participants’ ratings of various distributions. However, when we contrasted the process underlying participants’ rating decisions with that underlying their button pressing, we found that the activations of the parietal cortex and the insula were significantly larger in the former than in the latter condition. The activation of these brain area indicated that the participants were indeed processing the value, no matter the value was larger or smaller than the opponent’s. In addition, we also found that losers showed a stronger brain activation in association with the subjective rating in the insula than losers. This indicated that losers paid more attention and were emotionally more engaged in the second stage than winners.
In summary, we found that perception of fairness can be affected by the allocation of monetary reward. However, even when adequate attention is placed on the modulating factors that give rise to unequal monetary reward, individual difference might play a dominant role in fairness perception which is reflected in preference and satisfaction of monetary distribution. |
