It has been long thought that one of the characteristics that makes humans unique is our ability to learn and manipulate symbols for communication. However, this notion is starting to slowly unravel. Koko the gorilla knows sign language, and Alex the parrot was probably the most well-spoken bird to have ever existed. Also, a chimpanzee was trained to use Arabic symbols to add up sums as large as 4.
But that’s all child’s play; monkeying around, if you will. Now, PNAS reports that a team of Harvard and Yale researchers has trained rhesus macaque monkeys to recognize two sets of symbols, with 26 symbols in each set. And the monkeys demonstrated an ability to add them together!
The monkeys were given a touch-screen device that was divided in two halves. In the first stage of the experiment, the monkeys had to determine which side had the greater amount. First, they had to examine dots. Second, they had to examine Arabic numerals (1-9) or letters (which represented numbers 10-25).
Finally, they had to examine Tetris-like symbols which represented numerical values. To keep the monkeys playing, they were given drops of liquid treats that corresponded to the value they chose, regardless of whether they picked the right answer.
(For example, if the choice is between 4 and 8 and the monkey picked 4, he would get four drops.) Obviously, larger values mean more treats, so the monkeys had an incentive to learn how to recognize the larger value.