Double misinformation: effects on eyewitness remembering

Eyewitnesses may be exposed to multiple, mutually contradictory pieces of misinformation. In the simplest case of double misinformation, an original detail is targeted by misinformation A and then by misinformation B which contradicts A. In such situations, two separate mechanisms may produce opposite effects on eyewitness remembering: (1) multiple chances to be misled enhance the misinformation effect, and (2) noticing contradictions between multiple pieces of misinformation undermines credibility and decreases the effect (all relative to the effect of a single piece of misinformation). Across three experiments, we found support for both of these effects and confirmed an important moderating factor in an item analysis: the first mechanism dominates at low levels of misinformation (encoding and subsequent) availability, and the second at high levels (as this facilitates noticing contradictions). This means that, ironically, more misinformation can be less effective (in terms of distorting eyewitness memory or factual knowledge) if it contradicts itself.