經濟理論視複合樂透等價於同酬賞與機率之與簡單樂透，但過往文獻發現決策者或較偏好簡單樂透，違反此複合樂透之“轉換原則”（Reduction Principle）；再者，複合風險相關之神經經濟學研究，相對於簡單風險，亦見匱乏。本研究循此議題進行腦造影實驗，以期從行為與神經機制兩面向同時進一步探索相關現象與原因。一方面嘗試研究決策者面對任一形式樂透與確定金額間之風險態度是否不同；此間接比較讓研究者得以理解差異性之可能來源，並得以進一步檢驗轉換原則之普遍性。另一方面，本實驗亦試圖明瞭決策者評估相異呈現形式機率之能力與過程，是否存顯著差異，俾理解機率評估與樂透決策之關聯性。
　　本實驗共招募34位志願參與者（14位女性，均齡22.53歲），每位皆完成實驗過程之120道試驗。為數一半之試驗中，參與者需先評估以簡單或複合方式呈現之樂透，並在該樂透與隨後出現之固定金額間，擇其所偏好者；而在另一半試驗中，其先分別評估以複合或簡單方式呈現之圖示機率，再在其與後續呈現之數字機率值中擇其大者，其差距固定為0.03或0.08。
　　參與者行為之統計分析顯示，於機率評估時，當機率差距大時，或機率值離0.5愈遠，其表現將較佳。機率呈現方式雖對評估表現未有顯著影響，但機率差距變大對參與者在複合機率評估表現之改善，顯著甚於其在簡單機率下對評估表現之影響。在樂透選擇上，參與者之選擇在兩種風險呈現形態下有一致之表現且頗符合經濟理性思維；若樂透之期望值越高，變異數愈小，其越可能選擇樂透。風險型態對於決策者樂透選擇之影響，主要在面對複合樂透時，上述期望值對選擇之影響顯著較面對簡單樂透時為低。
　　腦影像資料分析亦發現神經機制處理資訊過程上之差異，在機率評估作業時，當機率以簡單方式呈現時，基底核(caudate)之血氧濃度變化與機率值高低呈顯著正相關；而當機率以複合方式呈現時，前額葉(medial frontal gyrus, MFG)、上側前額葉(dorsolateral prefrontal cortex, dlPFC)及多數上皮質區域之活化則是與機率值及0.5之絕對差距呈正相關。另一方面，在樂透選擇作業時，腦島前緣（anterior insula）在面對複合樂透時，有較面對簡單樂透時更明顯活化之現象；再者，於樂透評估階段時，參與者內側前額葉（medial prefrontal cortex, mPFC）之活化，在兩種樂透呈現方式下皆與樂透期望值呈顯著負相關，但僅在面對簡單樂透時，內腹側前額葉（ventromedial prefrontal cortex, mPFC）會與後續之固定值大小呈正相關；而該區域之血氧濃度，亦僅與固定值減簡單樂透期望值有顯著之正相關。
綜上所述，神經上，機率及決策相關訊息處理在兩種呈現方式下皆有所差異，以致參與者在簡單樂透下對決策相關之整合或相對價值之變化，有較面對複合樂透時更為靈敏之反應；反映在行為上，期望值差異對參與者之樂透選擇之影響，在複合樂透下，比其在簡單樂透下之影響較為不顯著。

We investigated the behaviors and neural mechanisms of decision-making facing compound and simple uncertainties with an fMRI experiment. In lottery tasks, participants pick between a lottery, simple or compound, and a certain reward. In probability tasks, participants chose the bigger number between a graphical probability, simple or compound, and a numerical probability.

Behaviorally performances in probability evaluations were better for probability values further away from 0.5 and for larger distances between probabilities. This improvement from larger distances was more significant in compound tasks than in simple ones. In lottery choices, higher expected values or smaller variances were related to higher likelihood of lottery choices. Nevertheless, this relationship was mitigated in compound tasks.

Neural activities in caudate revealed positive correlations with the probability values in simple probability tasks, but those in medial frontal gyrus, dorsolateral prefrontal cortex, and other cortical areas in compound tasks showed positive correlations with the absolute distances between probability values and 0.5. For lottery tasks, anterior insula exhibited stronger activations in compound than in simple tasks. Moreover, activations in vmPFC only showed positive correlations with the differences between certain values and the expected values in simple lottery tasks.

These findings jointly reflected that a higher neural sensitivity to changes in decision or integrated values when participants face simple than compound uncertainties may contribute to behavioral discrepancies.

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