O. M. G.
In the study in question, two experiments were done. In the first, people in a suburban mall were classified as high-income vs. middle income and asked to do cognitive tests while thinking about a hypotheical car repair. In the second, people in a rural, cyclical economy (in India) were asked to do similar tests before and after the harvest, when they were relatively "poor" or "rich". In each case, people in the "poor" condition did worse.
Who wouldn't do poorly on any kind of test while you're preoccupied with money? To conclude from this that poor people are cognitively inferior in general is specious. Though it makes a good headline and will serve the agenda of proponents of universal income schemes, the talk of "cognitive bandwidth" being impaired by poverty is bogus.
The position of the authors seems to be that people in poverty are always so preoccupied with finances they can't think straight. If so, they provide no proof for their thesis. I'd like them to go down to Wall Street and ask stock brokers to do these cognitive tests while thinking about government bailouts, or ask a restaurant chef to do them while contemplating that night's specials. It's a slippery slope: it seems to me that using this method you can pretty much prove anything you like about anyone.