Exploring whether nonhuman primates show a bias to overestimate dense quantities

Area of Science:

• Cognitive Science
• Comparative Psychology
• Neuroscience

Background:

• The density bias affects perceived numerosity based on item spacing, particularly in foraging contexts.
• This bias suggests that perceived quantity can be influenced by spatial arrangement, not just item count.

Purpose of the Study:

• To investigate if the density bias is a general perceptual phenomenon beyond foraging.
• To explore the relationship between the density bias and the Solitaire numerosity illusion in primates.

Main Methods:

• Capuchin and rhesus monkeys performed a computerized relative discrimination task.
• Stimulus size, interelemental distance, and array pattern were controlled.
• Results were compared to prior data on the Solitaire illusion in the same individuals.

Main Results:

• Capuchin monkeys demonstrated a significant density bias.
• Rhesus monkeys exhibited a weaker density bias.
• No correlation was found between density bias and Solitaire illusion susceptibility.

Conclusions:

• The density bias appears to be a general perceptual phenomenon in capuchin monkeys, extending beyond foraging.
• Individual differences in numerical perception exist, but the density bias and Solitaire illusion are distinct.
• Further research is needed to understand the mechanisms underlying these biases in non-human primates.