Nat. Neurosci. 20, 590–601 (2017); published online 20 February 2017; corrected after print 4 May 2017

In the version of this article initially published, the pink and gray symbols were switched in the key to Figure 7d and the plot of the outlier data points was mis-scaled relative to the axes. In Figure 6b, the x axis was numbered 0 through 1 instead of −1 through 0. The errors have been corrected in the HTML and PDF versions of the article.