JACKSON HOLE, WYO.–In an essay in The Wall Street Journal last month, Harvard University economist Lawrence Summers envisioned a world in which computers and machines displace a vast new array of human work, creating an economy that produced few opportunities and sources of income for actual people.

Taxis wouldn’t need drivers, nor retailers cashiers or banks financial analysts. “The challenge for economic policy will increasingly be generating enough work for all who need work for income, purchasing power and dignity,” he argued.

David Autor, a Massachusetts Institute of Technology economics professor, argues in a paper to be presented Friday to central bankers at the Kansas City Fed’s Jackson Hole symposium that automation is creating a different kind of problem for the economy. Rather than destroying jobs broadly, it is polarizing the labor market. While thinning out the ranks of middle-class jobs easily replaced by machines, he argues automation is increasing the ranks of low-skilled workers who perform tasks that can’t easily be displaced by machines — like cooks or home health workers — and the ranks of high-end workers with abstract thinking skills that computers can’t match.