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

Given a choice between a simple option offering a preferred-food item (e.g., a grape, G) and a combo option offering the same preferred-food item plus a less-preferred food item (e.g., a grape + a slice of cucumber, GC), animals often behave suboptim…

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