Babies know animals are not hollow

What distinguishes animals from inanimate objects? If you could ask eight-month-old babies, the answer might be that animals have stuff inside them. Researchers led by Peipei Setoh of the University of Illinois were able to suss out this intriguing world view by using the ‘stare test’.

It’s not surprising that by the time a child reaches school age, he or she understands that an animal’s insides are vital to its survival. As young as age three, children know that the insides of a living pig will be more similar to those of a living cow than to a piggy bank. How early on does this understanding arise? Babies can’t talk, but they can stare at things and they particularly like to stare at things they find puzzling or surprising.

In this case, 177 six to nine-month old infants were introduced to two novel items, a large striped can and a large colored box. The items moved around (apparently by themselves) and then appeared to quack or beep at the adult experimenter, who maintained the pretense that they were having a conversation. Thus having established that the items were self-propelled and cognitively aware, two hallmarks of being alive, the can or box was rotated to show the infant the bottom of the object. In each test, one of the objects (the can or the box) had an open bottom, showing that that object was hollow, and the other object was sealed so that the insides could not be viewed.

The babies stared longer at the hollow objects, indicating that this was not something they had expected to see. In contrast, when the can or box had not moved on its own and there had been no ‘conversation’ with the adult, babies found the closed and open items equally plausible. That is, they were not surprised that an object that didn’t do anything was empty inside.

These data suggest that very young children understand that it’s something in the insides of an animal that give it agency. They even seem to have some ideas about the composition of those insides. Experiments in which a self-propelled object appeared to rattle also startled the babies. Infants may not know much about the anatomy of living things, but they do know it shouldn’t rattle.

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