Monkeys overestimate connected arrays in a relative quantity task: A reverse connectedness illusion.

Area of Science:

• Cognitive psychology
• Comparative cognition
• Animal behavior

Background:

• Species exhibit consistent quantity judgments, influenced by Weber's Law and the ratio effect.
• Perceptual illusions, like the human connectedness illusion, reveal insights into quantity representation.
• The connectedness illusion causes underestimation of item quantity when elements are connected.

Purpose of the Study:

• To investigate if the connectedness illusion is present in non-human primates.
• To compare quantity judgments between humans and rhesus macaque and capuchin monkeys.
• To explore cross-species differences in perceptual biases related to quantity.

Main Methods:

• Pre-registered study design to ensure scientific rigor.
• Testing rhesus macaque and capuchin monkeys on quantity discrimination tasks.
• Comparing monkey responses to stimuli with and without connected items.

Main Results:

• Monkeys demonstrated a bias opposite to the human connectedness illusion.
• Monkeys consistently preferred arrays with connected items, perceiving them as more numerous.
• This indicates a significant difference in quantity perception between humans and these monkey species.

Conclusions:

• The connectedness illusion, as observed in humans, is not replicated in rhesus macaques and capuchin monkeys.
• Monkeys may have distinct mechanisms for quantity representation compared to humans.
• Further research is needed to understand the evolutionary and cognitive underpinnings of these cross-species differences.