Learning and caring and being rich

The study: People were presented with different sets of images in a sort of memory game. If I read it right, some images were associated with a picture of a coin and others were associated with a scrambled picture of a coin. The learners were told that they would actually receive a coin for every one they saw during learning.

Learning speed was negatively correlated with wealth, whether that was net wealth or income size. Basically, richer people had more trouble connecting the coin with its associated image than poorer people.

The conclusion of the authors wasn't that the rich people were less intelligent but rather that they cared less about the coins--they already had plenty.

While the intent of the study was to show diminishing returns of money as wealth increases, the thing that interests me the most is the assumption behind the study: that learning happens more quickly when you care more.