Color categories in macaques.

This experiment investigated whether macaque monkeys partition the photic spectrum into the same four basic hue categories that humans do, i.e., blue, green, yellow, and red. Monkeys were trained to respond in the presence of one chromatic stimulus and were tested, in extinction, for generalization to others. In extinction, the monkeys responded at similar and high levels to stimuli that fell in the same basic human hue category as the training stimulus and at similar and much lower levels to stimuli that fell in a different human hue category from the training stimulus. It was concluded that macaques and humans categorize the spectrum in a similar fashion.