Modeling the effect of speed emphasis in probabilistic category learning

For many decisions in life, there is uncertainty about the outcome even if the stimulus is a familiar one. Under these circumstances, people often rely upon previous experience to make a choice. In general, more accurate responding is achieved when one considers decision-relevant information for longer. There are practical limits, however, to how long one can deliberate, and so decision-makers must balance decision speed against accuracy. Traditionally, the overall speed with which people respond has been understood in terms of changes in the evidence threshold used for decision-making. However, more recent findings suggest that speed pressure may also affect the quality of information people recruit for making decisions. The current study investigated the effects of emphasizing either response speed or response accuracy on decision-making in a probabilistic category learning task. Strikingly, conclusions from two model-based analyses of performance depended on whether data were analyzed at the level of individuals or the group average. For the group-level analyses, speed pressure selectively influenced evidence threshold. For the individual-level analyses, speed pressure affected both evidence threshold as well as the quality of information driving decision-making for four out of six participants. Our findings are consistent with recent results that identify common brain areas associated with setting evidence thresholds decision-making and representing category-level information in trial-by-trial associative learning