Trial-Type Dependent Frames of Reference for Value Comparison

A central question in cognitive neuroscience regards the means by which options are compared and decisions are resolved during value-guided choice. It is clear that several component processes are needed; these include identifying options, a value-based comparison, and implementation of actions to execute the decision. What is less clear is the temporal precedence and functional organisation of these component processes in the brain. Competing models of decision making have proposed that value comparison may occur in the space of alternative actions, or in the space of abstract goods. We hypothesized that the signals observed might in fact depend upon the framing of the decision. We recorded magnetoencephalographic data from humans performing value-guided choices in which two closely related trial types were interleaved. In the first trial type, each option was revealed separately, potentially causing subjects to estimate each action's value as it was revealed and perform comparison in action-space. In the second trial type, both options were presented simultaneously, potentially leading to comparison in abstract goods-space prior to commitment to a specific action. Distinct activity patterns (in distinct brain regions) on the two trial types demonstrated that the observed frame of reference used for decision making indeed differed, despite the information presented being formally identical, between the two trial types. This provides a potential reconciliation of conflicting accounts of value-guided choice.

认知神经科学领域的核心问题之一，是基于价值的决策（value-guided choice）过程中，个体如何对备选项进行比较并最终做出决策。目前已有明确共识：该过程需依托多项核心子流程，包括备选项识别、基于价值的比较，以及执行决策所需的动作实施环节。但目前仍不明确的是，这些子流程在大脑中的时间先后次序与功能组织方式。现有多种相互竞争的决策模型提出，价值比较过程可能发生在备选项动作表征空间，或是抽象商品表征空间中。我们推测，实际观测到的神经信号或许取决于决策所采用的框架。本研究采集了人类受试者完成基于价值的决策任务时的脑磁图（magnetoencephalography, MEG）数据，该任务中穿插了两种高度相似的试次类型：在第一种试次中，两个备选项会依次单独呈现，这可能促使受试者在每个选项呈现时分别估算其对应动作的价值，并在动作表征空间中完成价值比较；而在第二种试次中，两个备选项会同时呈现，这可能让受试者在选定具体动作之前，先在抽象商品表征空间中完成价值比较。两种试次下对应不同脑区的神经活动模式存在显著差异，这表明尽管两种试次呈现的信息在形式上完全一致，但受试者决策时所采用的参照框架确实存在区别。该发现为基于价值的决策领域中各相互矛盾的理论假说提供了潜在的统一解释思路。