Study finds infants wise eaters

A new Yale study discovered that infants are inclined to eat what they’re supposed to, after all.

As part of a larger investigation of how infants respond to plants, a pair of Yale psychologists found that while infants initially avoid touching plants, they also use social information from adults to learn that certain plants are edible. According to study authors, this finding provides the first evidence for the existence of social learning mechanisms in infants that allow them to identify edible plants.

“If you were walking down the street and you saw someone take an apple off a tree and put it in their mouth, that would seem fine,” said Annie Wertz, co-author of the study and postdoctoral researcher in Yale psychology department. “But if you saw that same person pull a chunk off of a fire hydrant and put it in their mouth, that would be pretty strange. Infants as young as six months of age seem to share those intuitions.”

The study is part of a larger project led by Wertz that aims to determine whether infants have specialized responses to plants.

In an earlier study co-authored by Wertz and Karen Wynn, a Yale psychology professor who is also an author on the most recent study, the researchers found that babies are reluctant to touch plants. When an object and a plant were placed in front of infants, the infants hesitated much longer to touch the plant, which is a hesitation that Wynn and Wertz viewed as an instinctive defense mechanism against the harm that poisonous plants may pose.

To investigate whether the reluctance could be overcome by social learning, Wertz and Wynn conducted four experiments at the Yale Infant Cognition Center with 6- and 18-month-olds. They predicted that infants would recognize a plant as a food source and choose to eat its fruits instead of a nonfood object, such as a metallic branch with fake fruits, after watching adults place both plants and the fake food in their mouths. After initial results confirmed their hypothesis, they ran another experiment in which infants were asked to choose between eating a plant and a fake food without watching an adult eat both objects first, and the infants did not show a specific preference for the plants. This indicates that while infants can quickly learn to identify plants as food sources, this generally only occurs after they are exposed to an adult safely eating the plant, Wynn said.

For the final part of the experiment, Wertz and Wynn found that when 6-month-olds watched adults eating fruits from a plant and fruits from an artificial object, they looked longer when the adults were consuming fruits from the object. Infants were already biased to identify the plant as a food source, Wynn said, and therefore did not spend as much time watching the adults eat fruit from the plant.

“This is an intriguing study suggesting that humans may be biologically prepared to learn about plants both in terms of the dangers that they pose and in terms of their edibility,” Frank Keil, a Yale psychology professor uninvolved in the study, said in an email. “It raises important questions about the underlying psychological mechanisms that could be responsible for such learning biases.”

Both this and the previous study have given researchers much insight into both the relationship between infants and plants, and the ability of infants to make inferences based on social cues, Wertz said.

“I really like our findings because they show that babies make both positive and negative inferences with plants,” Wynn said. “While they’re inhibited to reach out and touch a plant, they’re ready to make an inference with the right sorts of information — that plants are food.”

Wertz said she is currently working on testing whether infants are able to generalize learned information about plants. The previous study also showed that infants’ hesitation to touch plants lasted only a few seconds, and Wynn said she is interested in what might be going on cognitively during that period. Wynn said she would also like to find out if babies have a heightened sensitivity to negative social information by testing if babies are more mindful when they hear “no” from their parents.

The study was published online in the journal Psychological Science on Jan. 29.

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