Can rhesus monkeys spontaneously subtract?

Area of Science:

• Comparative Cognition
• Primate Behavior
• Numerical Cognition

Background:

• Many animals demonstrate numerical abilities, often requiring extensive training.
• Recent research explores spontaneous numerical understanding in animals and human infants.
• Understanding non-verbal numerical computation is key to understanding brain function.

Purpose of the Study:

• To investigate the capacity of rhesus monkeys for spontaneous numerical computation.
• To examine their ability to calculate the outcome of subtraction events without prior training.
• To explore the limits and conditions of their spontaneous numerical representations.

Main Methods:

• Eleven experiments were conducted with semi-free-ranging adult rhesus monkeys.
• A novel method involved presenting objects on occluded stages, followed by subtraction events.
• Monkeys chose between stages, with food rewards indicating correct computation of subtractions.

Main Results:

• Rhesus monkeys accurately computed subtraction outcomes for quantities of three or fewer items.
• Performance was maintained even with differing object identities and when distinguishing food from non-food items.
• Monkeys demonstrated representation of zero and equality in numerical comparisons.

Conclusions:

• Rhesus monkeys possess spontaneous numerical subtraction abilities, challenging previous training-dependent models.
• These findings suggest sophisticated numerical processing in non-human primates.
• The study contributes to understanding the neural basis of number representation in animals lacking language.