Ability of chimpanzees to respond to symbols of quantity in comparison with that of children and of monkeys.

Four chimpanzees, 4 rhesus monkeys, and 11 children aged 4-9 yr were assessed under comparable conditions for their ability to make use of colors as symbols of quantity. One particular color represented the quantifier "all"; another represented "some"; another represented "one"; a fourth represented "none." These arbitrarily chosen colors retained their individual meanings when the test conditions were varied on three occasions. The ability of the subjects to continue responding appropriately to the colors immediately after a change of test condition was used as the measure of performance. The apes performed like the monkeys, having especial difficulties relative to the children with the most sensitive quantifier "some."