Asymmetries in stimulus comparisons by monkey and man.

Area of Science:

• Cognitive Psychology
• Comparative Cognition
• Neuroscience

Background:

• Similarity is fundamental to cognition, often modeled as distance in stimulus space.
• Human similarity judgments are asymmetric, influenced by factors like prototypicality (e.g., 99 is more similar to 100 than vice versa).
• It was unknown if such asymmetries exist in nonhuman primates.

Purpose of the Study:

• To investigate whether rhesus monkeys display asymmetric similarity judgments.
• To compare human and macaque patterns of similarity asymmetry.
• To explore potential neurophysiological underpinnings of these judgments.

Main Methods:

• Four rhesus monkeys performed a temporal same/different task.
• Error patterns were analyzed to detect asymmetries in stimulus comparison.
• A control study with human participants was conducted for comparison.

Main Results:

• Monkeys demonstrated asymmetric error patterns in similarity judgments.
• Monkeys perceived smaller differences when the first stimulus was less prototypical than the second, mirroring human findings.
• Individual differences in asymmetry patterns were observed in monkeys, also present in humans.

Conclusions:

• Asymmetric similarity judgments are present in rhesus monkeys, challenging the notion of this being a uniquely human trait.
• These findings suggest conserved mechanisms for stimulus comparison across species.
• Relatively simple neurophysiological mechanisms may underlie complex similarity judgments in both humans and macaques.