The 'less-is-better' effect in capuchin monkeys (Sapajus sp.): Some data and a contrast-like hypothesis

Area of Science:

• Animal behavior
• Cognitive science
• Primate studies

Background:

• Animals often make suboptimal food choices, preferring simpler options or showing indifference when offered a preferred food alone versus with a less-preferred item.
• Existing hypotheses, like the selective-value and average-quality hypotheses, fail to unify explanations for both indifference and the 'less-is-better' effect.

Purpose of the Study:

• To investigate capuchin monkeys' food choice behavior in simple and complex scenarios.
• To test the selective-value and average-quality hypotheses.
• To propose a unified account for observed suboptimal choices.

Main Methods:

• Six capuchin monkeys (Sapajus sp.) were presented with various choice tests involving preferred and less-preferred food items.
• Tests included simple choices (preferred + less-preferred vs. preferred) and complex choices (e.g., two preferred + one less-preferred vs. three preferred + one less-preferred).
• A final sample of four individuals per test was used.

Main Results:

• Capuchin monkeys demonstrated suboptimal behavior, including indifference and the 'less-is-better' effect.
• Findings suggest that the value of the less-preferred food item can become negative due to contrast effects.
• The study observed that animals may avoid options containing less-preferred items.

Conclusions:

• The selective-value hypothesis can be expanded to explain both indifference and the 'less-is-better' effect by incorporating negative values for less-preferred items.
• A unified, process-based account can explain these suboptimal choice behaviors.
• The value of less-preferred items can be diminished or become negative, influencing animal decision-making.