Better generalization through distraction? Concurrent load reduces the size of the inverse base-rate effect

The inverse base-rate effect (IBRE) is an irrational phenomenon in predictive learning. It occurswhen people try to generalize what they have experienced to novel and ambiguous events. Thisirrational generalization manifests as a preference for rare, unlikely outcomes in the face ofambiguity. At least two formal mathematical models of this irrational preference (EXIT, NNRAS)lead to a counter-intuitive prediction: the effect reduces under concurrent load. We tested thisprediction across two experiments (N1 = 72, Mage = 20.12; N2 = 160, Mage = 20.88). We confirmthe prediction, but only when participants were under an obvious time constraint. This empiricalconfirmation is as surprising as the prediction itself—irrationality reduces under increased taskdemands. Further, our data are more consistent with the NNRAS model than with EXIT, the mostprominent model of the IBRE to date.