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Even Infants Understand “No Pain, No Gain”

A new study suggests that babies expect others to make logical cost-benefit decisions — and express surprise when they do not.

Infants as young as 10 months old make cost-benefit analyses and understand that one should put maximum effort only into worthy goals, according to a new study in Science. 

Researchers tracked infants’ gazes as they watched animated video clips, and found that infants stared longer at counterintuitive scenarios. For instance, when a character chose to jump over a barrier or scale a ramp for an undesirable reward, the babies stared at the screen as though scandalized. Otherwise, they gazed with fleeting interest.

“Regardless of whether an agent cleared higher barriers, climbed steeper ramps, or jumped wider gaps for one target over the other, infants expected the agent to choose that target at test,” the authors write. “Across all experiments, infants looked longer at the lower-value action.”

This isn’t the first study to demonstrate that infants can distinguish between valuable objects and lesser prizes. Researchers have previously found that, if an infant sees an adult consistently choose one item over another, they attribute more value to the favored item. But until now, scientists did not know whether infants were capable of taking the next mental leap. Do babies understand that it makes sense to expend more effort to obtain high-value items? And if so, are they surprised when others act irrationally?

To answer these questions, the researchers presented whimsical animated clips to 80 infants. The first clip established the “value” of a given interaction. For instance, one clip shows a smiling red ball choosing to glide over to its friend, a yellow triangle, rather than a blue rectangle. By looping this clip over and over again, researchers taught the infants that, for the red ball, meeting the yellow triangle was a more valuable goal than meeting the blue rectangle. Then, they showed the infants a video that placed some barrier between the red ball and each goal (the high-value triangle or the low-value rectangle).

Sometimes, the red ball did exactly what one would expect — it cleared even substantial barriers to visit the triangle, but would refuse to traverse tricky barriers to visit the rectangle. When this happened the infants looked on, unimpressed. But sometimes the red ball did the unthinkable. It would go to great lengths to visit the low-value rectangle, jumping barriers and climbing steep ramps, but refuse to exert even minimal effort to visit the high-value triangle! When this happened the infants stared, presumably surprised.

The researchers explain that when infants gazes at illogical scenarios, that’s their non-verbal way of indicating that they understand that something is amiss. “If infants infer the reward of the targets to the agent from the effort undertaken to reach them, then they should be more surprised when the agent chooses the lower-value target, looking longer at the test trials displaying that action,” they write.

The results are fascinating, but they’re not a slam dunk for baby cognition. First of all, the entire study hinges on the assumption that, when an infant gazes at something for a longer period of time, this means that the infant is confused. But even if we assume that’s true, this study merely demonstrates that babies expect characters to physically exert themselves for high-value goals. Whether they’re making cost-benefit analyses (and whether they’d feel the same way about mental exertion, for instance) remains unclear. 

Regardless, the findings suggest that children assign values to objects long before they’re able to verbally explain why. The study also implies that 10-month-olds have the mental hardware to expect others to act rationally—and to feel surprised when they don’t. “Before human infants learn to walk, leap, and climb, they leverage mental models of agents and actions,” the authors write. “Forward models of how agents plan, and inverse models for working backward from agents’ actions to the causes inside their minds.”