How Do Babies Know If Something Is Alive?

When my son Edwin was about three months old, he started talking. Not with real words of course, or any language that is understandable, but when I talked to him, he suddenly started responding by using babbles or raspberries or whatever sound he could muster.

What’s interesting is that these first attempts at communication weren’t just directed at me, but they were also directed at other people, and in some cases, inanimate objects, like the stuffed sheep he had in his crib. In fact, he’d wake up every morning and babble to his sheep while he waited for me to come to get him, as if he was chatting about the weather or about what he planned to do that day.

How did he decide who or what to interact with? How do babies figure out what’s alive and what’s not?

Source: Vanessa LoBue

Human Features of Living Things

From a very early age, there is evidence that babies pay a lot of attention to some important features of living things that might make learning about what’s alive and what’s not a bit easier. First, even from birth infants have a bias to look at things that have faces (Johnson & Morton, 1991), and they develop a preference for their mothers’ face within the first two months of life (Maurer & Salapatek, 1976).

There is also evidence that newborns prefer to look at things that move like people—what researchers call biological motion—over things that move mechanically (Simion, Regolin, & Buff, 2008). For example, 4- to 12-month-olds prefer to look at videos of animals over things like cars, boats, and helicopters. They also direct more emotional responses—almost all of them positive—to the animals, often smiling, laughing, or waving at them (DeLoache, Pickard, & LoBue, 2011), and talk to animals more than they talk to toys (LoBue, Bloom Pickard, Sherman, Axford, & DeLoache, 2013).

Based on this research, you might not find it surprising that having a face is a particularly important cue about what’s alive, which is likely why Edwin judged his stuffed sheep to be an appropriate conversation partner. For example, in a clever set of studies, researchers presented infants with a brown fuzzy stuffed blob about the size of a small dog. The blob either had a face or no face, and researchers found that infants would shift their attention to whatever direction the blob was facing if it had a face, suggesting that faces are a cue for whether an object is alive, and whose gaze might be an important cue for where to look next (Johnson, Slaughter, & Carey, 1998).

Other human-like parts might also be a cue for when something is alive, like hands or even legs (Rakison & Butterworth, 1998). To illustrate, another group of researchers showed 5- to 9-month-old babies two toys, a ball and a bear, and they watched as a person’s hand reached for one of the objects. After watching the person reach for the same object over and over again, the researchers switched the location of the two objects, and the person now reached for the same object in a different location as before, or a different object in the same location as before.

The researchers found that the babies were surprised (and looked longer) when they saw the person reach for the new object, not the new location—a finding that the researchers interpreted as evidence that babies were paying the most attention to the person’s intended goal. Importantly, babies didn’t show this response when they saw the same series of events with an inanimate stick instead of a person reaching for the objects, suggesting that they knew that people—not sticks—can have goals in mind (Woodward, 1998).

Non-Human Features of Living Things

Although human-like characteristics are probably a really good cue for when something might be alive, they aren’t the only cues that babies can use. Indeed, there are lots of living things that aren’t human and don’t have features like faces, such as worms, snails, and jellyfish. How do babies know that these things are alive?

Researchers have shown that even when something doesn't look human and doesn't have a face, babies can use self-propelled motion—or objects that move by themselves—as another cue for animacy. Using a similar study design as the one I just described, where a human hand or a stick reached repeatedly for an object, researchers found that 9- to 12-month-old babies expected the stick to reach for a new object if they saw the stick move by itself first and attempt to pick up one of the objects (Biro & Leslie, 2006). This suggests that babies expect objects that move by themselves to have goals, even if they don’t have faces, hands, or feet.

One final feature that infants use to decide whether an object is alive is whether it responds when the infant talks to it. In another study using the brown fuzzy blob described above, experimenters programmed the blob to respond to babies every time they babbled: Whenever the baby babbled, the blob babbled back. When the blob responded to the baby, the baby shifted its gaze to look wherever the blob appeared to look, even if the blob didn’t have a face (Johnson, Slaughter, & Carey, 1998).

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Bottom Line

Altogether, this research suggests that there are a lot of different cues babies can use to decide if something is alive. In reality, most things that are alive have many of these features all at once—they have faces, they respond to you, and they move by themselves. But the fact that babies can just use one or two of them creates the flexibility to decide that new animals like jellyfish might also be alive even though they don’t share all of the features that humans have. It also explains why just having a face might lead to some interesting conversations between your baby and some of his toys, or why that favorite stuffed animal can become such an important friend.

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