Quantity matching by an orangutan (Pongo abelii).

Area of Science:

• Cognitive ethology
• Comparative psychology
• Primate cognition

Background:

• Understanding numerical cognition in non-human primates provides insights into the evolution of number sense.
• Orangutans (Pongo abelii) are great apes with complex cognitive abilities, but their quantitative reasoning remains less explored compared to other primates.

Purpose of the Study:

• To investigate the numerical abilities of an orangutan using delayed matching-to-sample tasks.
• To determine if orangutans can discriminate quantities based on visual stimuli and generalize this ability to novel numerosities.

Main Methods:

• An adult male orangutan was trained on delayed matching-to-sample (DMTS) tasks involving stimuli with varying numbers of animals, shapes, or dots (1-10).
• Perceptual features like spatial arrangement and background color were varied, and dot size was manipulated.
• Performance was analyzed based on the absolute difference and ratio between comparison stimuli quantities.

Main Results:

• Orangutan performance was independent of perceptual variations but sensitive to numerical differences and ratios.
• Performance did not strictly follow the analog magnitude model's linear predictions.
• The orangutan demonstrated significant transfer to novel numerosities up to ten.

Conclusions:

• Orangutans possess robust quantity estimation abilities, extending to larger numerosities than typically subitized by humans.
• This suggests a more developed numerical cognition in orangutans than previously assumed.
• The findings contribute to understanding the comparative and evolutionary aspects of numerical cognition.