Public Release: 

Infants understand that more desirable rewards require more effort

American Association for the Advancement of Science

Infants who observe someone putting more effort into attaining a goal attribute more value to it, a new study finds. Past work has shed light on ways in which infants come to realize the differences in the value of an object; for example, if a person consistently chooses one item over another, infants will attribute more value to the selected item. Yet, it remains to be determined whether infants can grasp concepts of reward and associated "cost." Here, Shari Liu and colleagues presented ten-month-old infants with animations in which a character was faced with varying costs in order to achieve a goal; for example, in one scenario, the character had to jump over either a low wall or a much higher one to get its reward. If the cost of acquiring the reward was too much, the character would refuse to expend the effort to retrieve it. The researchers monitored as infants watched these test events, observing the lengths of their gazes. The researchers ran two additional and similar experiments in which the character had to climb a ramp or jump a gap to retrieve the reward, to ensure that it wasn't just speed or height that mattered, to infants' perception of cost, but indeed the effort exerted. Regardless of whether a character cleared higher barriers, climbed steeper ramps, or jumped wider gaps to reach one target over the other, infants gazed longer at the scenario in which the character went after the less desirable reward, which indicated they were surprised by the choice. They expected the character to prefer the goal it attained through costlier actions. Thus, it appears that infants are able to assign greater value to rewards that are more costly to attain.

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