Remembering past exchanges : apes fail to use social cues

The authors thank the Danish National Research Foundation [DNRF89] for funding.Nonhuman primates can remember events from their distant past. Furthermore, they can distinguish between very similar events by the process of binding. So far, research into long-term memory and binding has focused on the binding of contextual information, such as spatial surroundings. As such, we aimed to investigate if apes can bind and retrieve other types of information, specifically, social information. We presented great apes with three different object types; they learnt to exchange (via reinforcement) one of the object types with one experimenter and another type with a second, different, experimenter. The remaining object type was not reinforced by either of the experimenters. After a delay of two or ten weeks, we assessed the apes’ memory of which object type was exchanged with which experimenter. Additionally, we introduced a new experimenter to see if the apes could infer by exclusion that the remaining object type should be exchanged with the new experimenter. The apes successfully remembered which object types were exchanged, but failed to distinguish which object type was exchanged with whom. This failure to bind an object type to a specific person may have resulted from the apes learning to use a rule based on recency, as opposed to learning a conditional rule involving social information. However, results from a second experiment suggested they fail to incorporate social information even when no other information could guide successful performance. Our findings are consistent with research showing long-term memory in primates, but suggest that social information may not be bound in memory as readily as spatial or contextual information.Publisher PDFPeer reviewe

Annual report of activities of the College of European and Regional Studies in the year 2011

This research was funded by the Danish National Research Foundation (DNRF89).We examined if apes spontaneously remember one-time, distinctive events across long delays when probed by discriminant cues. Apes witnessed an experimenter hide a cache of food, which they could then retrieve. They retrieved one of two food types; one more distinctive than the other. Two, 10 or 50 weeks later, the apes returned to the same enclosure and found a piece of the previously hidden food on the ground. An experimenter who had not hidden the food was also present. Apes immediately searched the location where the food was previously hidden (no food was here), showing recall of the event. One week later, apes returned to the same enclosure, with the same food on the ground, but now the experimenter that had hidden the food was present. Again, apes immediately searched the hiding location. Apes that had not witnessed the hiding event did not search. There was no significant effect of food type, and retention declined from exposure to the two-week delay, then levelled, consistent with the forgetting curve in humans (Ebbinghaus, H. 1964 Memory: a contribution to experimental psychology (transl. H.A. Ruger & C.E. Bussenvis). New York, NY: Dover. (Original work published 1885.)). This is the first study to show apes can recall a one-time, non-goal-directed event longer than two weeks ago and that apes' recall declines in accordance with a standard retention function.PostprintPostprintPeer reviewe