Infants’ sense of inequality

Inequality has been much in the news recently with the Occupy protests, with which I have a great deal of sympathy:

It has often been argued that people (and even capuchin monkeys!) have an innate sense of fairness, in that they prefer resources to be distributed equally rather than unequally in experimental situations. Jonah Lehrer at Wired Science goes over some of the science behind this in a good recent blog post. But he doesn’t include any developmental evidence. Two new studies reveal that by 15 months, infants are already sensitive to how resources are distributed.

In the first study, published in Developmental Science by Alessandra Geraci and Luca Surian from the University of Trento, 12-18-month-old infants watched two animated characters taking turns to distribute two tokens to two other characters: either one token each, or both to one character. Subsequently, infants looked longer at animations where a chicken (which had observed the distribution of the tokens) approached the “fair” distributor than at animations where they approached the “unfair” one. The authors interpret this as implying that the infants preferred this scenario (approaching the fair distributor) – though it has to be pointed out that if the reverse pattern had been found, they might have interpreted this as showing surprise that the chicken would approach the unfair distributor (a common failing of this sort of “preferential looking” paradigm!). A more solid finding (in my view) was that when given pictures of the two distributors’ characters to play with, infants preferred to take the picture of the fair distributor.

A similar experimental design with similarly aged infants, recently published in PLoS One, obtained rather orthogonal results. Marco Schmidt (of the Max Planck Institute for Evolutionary Anthropology) and Jessica Sommerville (of the University of Washington) also showed 15-month-old infants a video of a character doling out equal or unequal amounts of milk or cookies to two other characters (see diagran below):

This time, the infants looked longer (on average) at the “unfair” outcome, which (the authors argue) implies that they were surprised by it (see what I mean about the selective interpretation of preferential looking results). Geraci and Surian, by contrast, had found no difference in looking times between the fair and unfair outcomes – just in looking times for the chicken’s approach to the other characters. Unfortunately, Schmidt and Sommerville did not test whether children preferred to play with the fair or the unfair distributor. But they did look at the children’s own sharing behaviour, in terms of whether they gave a play partner a preferred or a less preferred toy. They found that those children who looked longer at the unfair outcome (i.e., were more surprised by it) were more likely to give their partner their preferred toy; while those who looked longer at the fair outcome were more likely to hand over the less appealing toy. This is a nice little addition to the experiment, since it hints at how personality differences affect attitudes to fairness, even so early in life (I complained in a previous post about how psychologists too often interpret quite small mean differences between groups/trials, driven by a minority of participants, as indicating universal psychological principles).

So what can we say from all this about infants’ sense of fairness? Both pairs of authors argue that their results show that a concern with equality starts very early – much earlier than in the classical theories of Piaget and Kohlberg (who thought that it only appeared with the onset of middle childhood, around age 6-7). But taken together, their results are less supportive of this argument than when considered separately. The problem is that if infants looked longer at the unfair outcome in Schmidt & Sommerville’s experiment because they were surprised by it, then surely in Geraci & Surian’s experiment their longer looking times when the chicken approached the fair distributor should also indicate surprise.

Moreover, Schmidt & Sommerville undermine the first part of their experiment when they highlight, in the second part, that almost half of their participants looked longer at the fair outcome! Such a pattern of results hardly supports a simplistic interpretation in terms of a general preference for fairness. The strongest finding from these two experiments is perhaps that 14 out of 20 16-month-old infants in Geraci & Surian’s study preferred to play with the fair distributor (3 preferred the unfair distributor and 3 failed to choose). As I say, it was a pity that this was not replicated in the other experiment, as manual choice seems a more reliable way of assessing preference than looking times.

So while I would love to say that infants have an innate preference for fair distribution of resources, the evidence is just not conclusive at this stage. The most that we can say is that infants are sensitive to the proportions in which resources are distributed (at 15 months but not at 10 months). The theories of Piaget and Kohlberg that true norms of equality do not arise until a few years later may be more intact than the authors imply in their Discussion sections.

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