The hare and the tortoise: emphasizing speed can change the evidence used to make decisions

Decision-makers effortlessly balance the need for urgency against the need for caution. Theoretical and neurophysiological accounts have explained this tradeoff solely in terms of the quantity of evidence required to trigger a decision (the "threshold"). This explanation has also been used as a benchmark test for evaluating new models of decision making, but the explanation itself has not been carefully tested against data. We rigorously test the assumption that emphasizing decision speed versus decision accuracy selectively influences only decision thresholds. In data from a new brightness discrimination experiment we found that emphasizing decision speed over decision accuracy not only decreases the amount of evidence required for a decision but also decreases the quality of information being accumulated during the decision process. This result was consistent for 2 leading decision-making models and in a model-free test. We also found the same model-based results in archival data from a lexical decision task (reported by Wagenmakers, Ratcliff, Gomez, & McKoon, 2008) and new data from a recognition memory task. We discuss discuss implications for theoretical development and applications.