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Conceptual numerousness judgments by squirrel monkeys.

R K Thomas, D Fowlkes, J D Vickery

The American Journal of Psychology

|June 1, 1980

Summary

Monkeys demonstrated the ability to discern fewer items between two visual options, indicating conceptual numerical understanding. This challenges previous notions about numerical cognition in nonhuman animals.

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Area of Science:

Comparative psychology
Animal cognition
Numerical cognition

Background:

Understanding numerical cognition in nonhuman animals is crucial for evolutionary studies of cognition.
Previous research has explored numerousness discrimination in various species, with varying degrees of success.

Purpose of the Study:

To investigate whether monkeys can make conceptual judgments about numerousness.
To determine the limits of numerousness discrimination in nonhuman primates.

Main Methods:

Monkeys were trained to identify the card with fewer items (filled circles of varying sizes).
Area and brightness cues were controlled to isolate numerousness as the primary discrimination factor.
Training progressed through increasingly difficult numerical pairs, from 2:7 up to 8:9.

Main Results:

Both monkeys successfully discriminated numerousness up to the 7:8 ratio.
One monkey achieved criterion on the 8:9 numerousness discrimination task.
Controlled variables prevented reliance on non-numerical cues.

Conclusions:

Monkeys exhibit conceptual numerousness judgments, extending beyond simple perceptual discrimination.
The findings suggest that sophisticated numerical cognition is present in monkeys, similar to apes.
This study provides evidence for advanced numerical abilities in nonhuman primates.

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