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PECOS-9 comments on A New Interpretation of the Marshmallow Test - Less Wrong

73 Post author: elharo 05 July 2013 12:22PM

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Comment author: PECOS-9 04 July 2013 04:31:30PM 1 point [-]

I really don't see how this casts doubt on the original experiment. Suppose we express a child's decision as maximizing expected reward minus the cost of waiting, where the latter takes "self control" as a parameter. If we lower expected reward, (nearly) all the kids eat the marshmallow. If we raise expected reward (by reinforcing waiting twice), about half the kids wait. But still, 6/14 kids in the second group didn't wait, so clearly there's variance from another source.

The other source of variance could still be the children's "trustingness." The more trusting children could have a higher expected reward even after the kids are shown that the adults are reliable/unreliable. So the results are consistent with both of the following hypotheses:

  • More trusting children will wait longer and self control is not relevant
  • More trusting children will wait longer and children with more self control will wait longer

But this experiment ruled out the following:

  • It doesn't matter if a child is more trusting; only self control affects how long they wait
Comment author: framsey 04 July 2013 05:02:57PM 5 points [-]

But this experiment ruled out the following:

  • It doesn't matter if a child is more trusting; only self control affects how long they wait

I agree, but I don't think anyone believed that nothing else matters to marshmallow eating.

We have to distinguish between the propositions:

(P1) A significant fraction of the variance in marshmallow eating among children observed in past experiments is explained by trustingness.

(P2) Inducing large changes in trustingness in children produces changes in marshmallow eating behavior.

This study supports (P2), but it is only informative about (P1) to the extent someone previously assigned substantial probability mass to the proposition:

(P3) There is large variation in childrens' trustingness, but trustingness doesn't affect childrens' marshmallow eating decision.

I suspect most people didn't assign much probability to (P3), and so this study shouldn't change their opinion very much.

Comment author: PECOS-9 04 July 2013 05:14:51PM 2 points [-]

Agreed, but I think the reason this experiment is interesting is that it previously didn't occur to people (or at least to me) that trustingness is a possible alternative explanation of the classic marshmallow experiment, rather than self control. It was a blind spot.

Comment author: framsey 04 July 2013 05:23:39PM 3 points [-]

It didn't occur to me either, but ironically it was the first thing my wife suggested when I told her about the marshmallow experiment yesterday (it came up in the context of that professor's comments about fat people, self control, and PhD programs recently). This post's timing was thus quite serendipitous.

It probably occurred to her because she is a doctor who works with primarily poor patients, many of whom are black and hispanic, and so is used to the associated mistrust when crossing cultural and socio-economic lines.

Comment author: buybuydandavis 05 July 2013 08:51:37AM *  0 points [-]

I'm not so trusting, and it occurred to me.

EDIT: The key is to focus on what the experimental subjects observe, not the rules the experimenters intend to follow. The kid is promised another marshmallow, he doesn't know that he is going to get one, and he doesn't know that the one he has now won't be taken away. With priors associated with abuse, the kid should eat the marshmallow as soon as possible.