Primates and concept learning
Chapter 12 endnote 13, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:
In the lab, animals can learn additional concepts if you reward them with food or drink...
Under some conditions, non-human animals can learn sophisticated concepts. The key is making information relevant to the animal's body-budget. For example, if you teach a chimp that an abstract symbol, like a heart ♥, is associated with double letters like AA, BB, CC, and so on, and that a second symbol, #, is associated with AB, then the chimp can generalize that AA and BB are “the same.” The symbols allow chimps to perform induction, just as human infants do when they learn that the word “Dog” applies to both tiny Chihuahuas and huge Saint Bernards.[1]
But a chimp typically learns in this way only when rewarded with something that impacts its body budget.
So, another possibility is that the chimp is learning to request a reward in a complex way. They probably don't use symbols to communicate information for its own sake, the way a human infant would. This might be an example of using the symbol as an imperative (to request a reward).[2]