Jared Bernestein answers some questions

Q: What is the mechanism by which higher incomes from increases in productivity get back to workers?

A: Well, the problem is: it doesn’t.  I mean, sometimes it does, and it should, but in recent decades, productivity growth has diverged from the compensation and incomes of middle- and lower-income families.  This is really another way of saying inequality has grown.
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But of course one of the characteristics of growing inequality is that the average is less descriptive of outcomes throughout the income scale.  For years, through the 1950s and 60s, real MEDIAN family income kept pace with productivity growth—both about doubled in those years.  But since then, median family income has grown about one-third as fast as productivity growth.

What changed?  A lot—fewer unions, the shift from manufacturing to service jobs (hastened by the increase in trade with lower wage nations), outsized returns to folks in certain sectors, like finance, and the growth of the educational advantage, to name some of the more important factors.

But no small part of this disconnect comes under the heading of “bargaining clout.”  The benefits of productivity growth don’t naturally flow to those responsible for said growth.  Some people have to fight for it.  And I’m not just talking unions here. 

I think one of the most important answers to your question is “full employment.”  Labor markets were much tighter during the period noted above when median incomes grew with productivity, and when they got that tight for a moment in the latter 1990s, low- and middle-earnings again begin to rise with productivity.

In those years, employers had to bid compensation up to get and keep the workers they needed.  In that way, low unemployment was the “mechanism” you seek.  And yes, it’s been very much missing ever since.

This is a "structural" problem. Funny how conservatives only refer to "structural" problems when they're used as reasons for the futility of government action. During the Presidential campaign Obama referred to this structural problem in interviews with business and economics reporters for newspapers and magazines.. Supposedly in the Suskind book Obama is quoted as saying there's a productivity problem with labor, but maybe he was referring to that.