While some experiments try to test animals' perception of quantities in natural settings, others use training paradigms that offer experimenters more control over the conditions. All face the obstacle of distinguishing whether animals are reacting to numerosity or other perceptual features such as size, density, or mass, and it’s still an open question how widespread numerosity perception is. Below is a selection of findings highlighted by numerosity researcher Andreas Nieder in his 2019 book, A Brain for Numbers.
Beyond humans, multiple MAMMALS, including primates, dogs, cats, rodents, and dolphins, have shown an ability to discriminate between sets of objects based on the number of items they contain, both spontaneously and in return for a reward. Research suggests some animal species can perform counting, too: experiments in the 1950s (recently replicated in mice) found that rats could be trained to press a lever a set number of times between 4 and ...
