The effects of mental contamination on the hindsight bias: Source confusion determines success in disregarding knowledge

We present data from eight experiments in which we explored the effects of source confusion on the hindsight bias; participants' success in disregarding information when they were instructed to do so was affected by participants' level of source confusion. In Experiment 1 we demonstrated participants' failure to disregard Revolutionary War information they recently learned while reading an essay; this failure to discount was not affected by participants' essay reading times (Experiment 1a). In Experiment 2 participants successfully discounted obscure War of 1812 information; this discounted information remained available in memory (Experiment 2a). In a direct test of source confusion (Experiment 3) we showed that participants discriminated between presented and not‐presented War of 1812 information better than they discriminated presented and not‐presented Revolutionary War information. In Experiments 4 and 4a we tested and rejected a motivational explanation for our findings, namely that subjects voluntarily withheld information when asked to disregard it. We tested a debiasing technique in Experiment 5 and found it was successful in helping participants discount familiar information. Results throughout are discussed as being attributable to source confusion. Copyright © 2008 John Wiley & Sons, Ltd.