Observing evidence accumulation during multi-alternative decisions

Most decision-making research has focused on choices between two alternatives. For choices between many alternatives, the primary result is Hick's Law-that mean response time increases logarithmically with the number of alternatives. Various models for this result exist within specific paradigms, and there are some more general theoretical results, but none of those have been tested stringently against data. We present an experimental paradigm that supports detailed examination of multi-choice data, and analyze predictions from a Bayesian ideal observer model for this paradigm. Data from the experiment deviate from the predictions of the Bayesian model in interesting ways. A simple heuristic model based on evidence accumulation provides a good account for the data, and has attractive properties as a limit case of the Bayesian model. (C) 2009 Elsevier Inc. All rights reserved.