THE TWO-ALTERNATIVE-FORCED-CHOICE (TAFC) TASK

In most of the studies of the DM process the dynamics of the information gathering and elaboration are modeled under the so called Two-Alternative Forced-Choice (TAFC) task [1-3]. 

Choosing between two alternatives, even under time pressure and with uncertain information, is a simplification of many situations, but it is representative of many problems faced by animals in their natural environments (e.g., whether to approach or avoid a novel stimulus). The reduction of complex problems into nested easier dichotomous problems may also respond to evolutionary strategies for optimizing the speed-and-accuracy tradeoff. Bogacz and coauthors [4] evidenced that the TAFC task models typically make three fundamental assumptions:

 a) evidence favoring each alternative is integrated over time;

 b) the process is subject to random fluctuations;

 c) the decision is made when sufficient evidence has accumulated favoring one alternative   over the other. 

The major issue about the modality of integration of evidence is generally solved in favor of the integration of the difference in evidence, rather than the independent integration of evidence for each alternative. The leading theories, by assuming that the difference in evidence drives the decision, consider that  the differences can be computed by inhibitory mechanisms. Those theories essentially distinguish themselves by the mechanisms of inhibition that they adopt, by which they get to different behavioral predictions. The application of the diffusion models in the study of cognitive processes had been introduced by Ratcliff [1] and since then on they  had kept their theoretical soundness in the context of the analysis of decision making under uncertainty [2,5-12] because it is relatively simple and well characterized [13] and it has been proven to implement the optimal mechanism for TAFC decision making [14,15].

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