Fallacious reversal of event-order during recall reveals memory reconstruction in rhesus monkeys.

Whether nonhuman primate species can construct, still less reconstruct, order of past events remains controversial. Here we show that rhesus macaques are capable of reconstructing the temporal order of memory traces of dynamic videos. We made use of 2000 unseen naturalistic videos of wildlife content for encoding, and then probed monkeys' recollection of temporal-order of events with a temporal-order judgement (TOJ) test. This encoding-TOJ procedure was repeated at three different time points (day 1, day 2, and day 32+). We specifically tested for differential TOJ memory performance for videos that were displayed in a reverse sequence versus videos that were displayed in a normal sequence at these different time points. We observed that during TOJ monkeys committed more errors for video content that were shown in reverse but only upon re-exposures (i.e., day 2 and day 32+). Moreover, this memory distortion effect is significantly accentuated by social relevance of the video content. We interpret that the monkeys reversed the out-of-order events in accordance to their knowledge priors; such fallaciously re-ordered memory traces then led to higher rate of errors. Demonstrating in macaque monkeys a form of errors in temporal-order memory for reverse videos carries implications for studying memory retrospection in the primates.