Post-event misinformation effects in a language-trained chimpanzee (Pan troglodytes)

Errors of source monitoring are widespread human memory challenges, and our memories are subject to distortion upon the presentation of subsequent misinformation. Less is known about if and when misinformation effects occur in nonhuman species' memory. Here we tested a symbol-trained chimpanzee's recall memory of a hidden food item's identity after a 10-min delay. During this delay, the subject was sometimes (depending on the condition) shown consistent or inconsistent video information about the identity of the food, before being asked to name the item to a second experimenter blind to the reward and condition. Across all conditions, our subject, Sherman, correctly named the food item at above chance levels. In the Inconsistent condition, in which Sherman was shown a video with misleading information, his performance was the worst of all conditions (although accuracy was still high). Interestingly, however, during three of the four trials in this condition in which Sherman made a mistake, he incorrectly named the food item shown during the misleading video information. These results provide evidence that chimpanzees, like humans, may be vulnerable to misinformation effects, even when that misleading information is presented in a different modality (video) than the original live event memory, demonstrating further commonality between human and ape memory systems.