Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dual or Unitary System? Two Alternative Models of Decision Making

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dual or Unitary System? Two Alternative Models of Decision Making

Article excerpt

In recent years, a lively debate in neuroeconomics has focused on what appears to be a fundamental question: Is the brain a unitary or a dual system? We are still far from a consensus view. The accumulating evidence supports both sides of the debate. A reason for the difficulty in reaching a convincing solution is that we do not yet have a clear theoretical model for either position. Here I review the basic elements and potential building blocks for such theories, using sources in large measure from classical decision theory and game theory. Cognitive, Affective, & Behavioral Neuroscience

In recent years, a lively debate in neuroeconomics has focused on a fundamental question: Is the brain a unitary or a dual system? When facing a choice of an economic nature, we may formulate two hypotheses about how the final decision is made. According to one view, the brain acts as a unified system, in the role of information processor: This system elaborates the inputs provided by the description of the choices, and eventually produces a final decision. Different units may take part in the process, and each may provide separate elements for the evaluation of the available options. The activity of these elements is not controlled by any central unit, and coordination may require some way of integrating the inputs provided by the different units. No one of the units, however, can reach a decision on its own.

According to the alternative view, most of our choices, and all of the interesting ones, produce an internal conflict between two (or perhaps more) well-defined and complete preferences about the available outcomes. It may be useful to think of each such preference as a "self." The reason for this name is that each of these two selves could in principle reach a decision on its own, and from this point of view is very similar to an individual. When the potential choices of the two selves agree, the solution is naturally the commonly preferred choice. When they disagree, some way of resolving the conflict is necessary: For example, the intensity of the preference of each self may determine the option chosen, or a control unit may override the choice made by one of the units. Thus, an additional concept is needed to provide a prediction on the final outcome-for example, the Nash equilibrium concept.

After this brief review, the next section makes clear that a consensus view is still far from being achieved. The accumulating evidence supports both sides of the debate. A reason for the difficulty in reaching a convincing solution has been that we do not yet have a clear theoretical model of either of the positions. The purpose of this study is to review the basic elements and potential building blocks of such theories, using sources in large measure from classical decision theory and game theory.

Dual and Unitary Systems: Evidence

Three separate sets of experimental evidence have informed the ideas on this matter. If we focus only on economic choices that do not involve other individuals, three different environments have been considered.

Early and late rewards. The first environment involves choices among outcomes that occur at different points in time. For example, the subject has to choose between the payment of $10 today and the payment of $12 in a week. In this case, the two-selves hypothesis assumes a tension between short-run and long-run preferences. The shortrun preference favors immediate rewards and is less sensitive to future ones. The long-run preference has opposite inclinations, and so is more able to trade off the advantages of payments at different points in time.

In brain-imaging studies, the hypothesis that two systems may be simultaneously active when the choice is made should be reflected in differential activation of distinguishable neural systems. This is, of course, a necessary condition; the fact that different systems are activated, however, is not by itself sufficient to prove the dual-system hypothesis. …

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