Episodic memory, as defined by Tulving, can be described in terms of behavioural elements (what, where and when information)
but it is also accompained by an awareness of one’s past (
chronesthesia) and a subjective conscious experience (
autonoetic awareness). Recent experiments have shown that corvids and rodents recall the where, what and when of an event. This capability
has been called episodic-like memory because it only fulfils the behavioural criteria for episodic memory. We tested seven
chimpanzees, three orangutans and two bonobos of various ages by adapting two paradigms, originally developed by Clayton and
colleagues to test scrub jays. In Experiment 1, subjects were fed preferred but perishable food (frozen juice) and less preferred
but non-perishable food (grape). After the food items were hidden, subjects could choose one of them either after 5 min or
1 h. The frozen juice was still available after 5 min but melted after 1 h and became unobtainable. Apes chose the frozen
juice significantly more after 5 min and the grape after 1 h. In Experiment 2, subjects faced two baiting events happening
at different times, yet they formed an integrated memory for the location and time of the baiting event for particular food
items. We also included a memory task that required no temporal encoding. Our results showed that apes remember in an integrated
fashion what, where and when (i.e., how long ago) an event happened; that is, apes distinguished between different events
in which the same food items were hidden in different places at different times. The temporal control of their choices was
not dependent on the familiarity of the platforms where the food was hidden. Chimpanzees’ and bonobos’ performance in the
temporal encoding task was age-dependent, following an inverted U-shaped distribution. The age had no effect on the performance
of the subjects in the task that required no temporal encoding.
Keywords Episodic-like memory - Age - Great apes