Paradoxical effects of base rates and representation in category learning

Abstract

The inverse base rate effect (IBRE) continues to be a puzzling case of decision making on the basis of conflicting information in human category learning. After being trained via feedback over trials to assign combinations of cues to high- and low-frequency categories, participants tend to respond with the low-frequency category to an otherwise perfectly conflicting pair of test cues, contrary to the category base rates. Our Experiment 1 demonstrated that decision making on the basis of an explicit summary of the cue-outcome and outcome base rate information from the standard learning task does not result in the effect. The remaining experimental conditions evaluated the necessary and sufficient conditions for the effect by systematically exploring experimental deviations between the standard learning task and the pure decision-making task. In partial disagreement with both recent theoretical accounts of the effect, these experiments indicate that asymmetric outcome representation and profound base rate neglect are individually necessary and jointly sufficient conditions. Broader theoretical implications are discussed.

No evidence for rule-based processing in the inverse base-rate effect

“…On the basis of these results, Winman et al (2005) concluded that rule-based processes play an essential role in producing the inverse base-rate effect. However, these conclusions were contradicted by the results of a series of experiments by Johansen, Fouquet, and Shanks (2007). Johansen et al explored the conditions under which the inverse base-rate effect occurred by systematically manipulating the way in which information about the task was presented to the participants.…”

Linguistic markedness and category learning

“…This has led to a lively debate regarding when and for what reason inverse base rate effects occur (e.g., Johansen et al, 2007;Juslin, Wennerholm, & Winman, 2001;Kruschke, 1996). The typical task used in experiments demonstrating the inverse base rate effect is based on medical diagnosis.…”

“…There is also an extensive body of research on the effect of category frequency*typically referred to as base rates*on category learning (Johansen, Fouquet, & Shanks, 2007;Kahneman & Tversky, 1973;Kruschke, 1996;Maddox, 1995;Medin & Edelson, 1988). Interestingly, while base rates do often affect classification behaviour, they do not always do so in a consistent way.…”

Effect of a context shift on the inverse base rate effect

“…Two other studies of the IBRE have also presented a novel cue at test. Johansen, Fouquet, and Shanks (2007) reported preferentially-rare responding, but did not statistically analyze those data, and used a procedure quite unlike those of other IBRE experiments. Don and Livesey (2017) reported preferentially-common responding, but they presented the novel cue in compound with familiar cue A, which makes their result hard to interpret.…”