Science 358, 1038–1041 (2017)

Credit: Imagezoo / Alamy Stock Photo

We invest more effort to get hold of objects that are dear to us compared with those we value less. Conversely, by observing how much effort someone invests obtaining an object, we can learn about their preferences — and potentially about the object’s true value. Learning the value of actions is important for children, but whether they can infer value from observed effort is unclear.

Shari Liu, of Harvard University, and colleagues show that ten-month-old infants can judge the value of an object from observing the effort actors spend. In three experiments, infants watched a cartoon character jumping a higher fence, climbing a steeper hill and leaping across a wider trench for one object, but not for another. The researchers then measured infants’ interest when the actor chose the object they were previously less willing to exert effort for when no effort was involved in obtaining either object. Children showed a higher level of interest in this choice, indicating that they had learned which object had a higher value.

It is an open question whether infants also have concepts of non-physical effort, or risk, and can take these into account when judging the value of goals based on observed behaviour.