AFTER CAUSING A STIR when she announced the lengthy, provocative title of her latest exhibition at Sikkema Jenkins, Kara Walker is being honored with a W.E.B. Du Bois Medal from Harvard University's Hutchins Center for African & African American Research. Walker is among eight recipients of the 2017 award, including filmmaker Ava DuVernay, Librarian of Congress Carla Hayden, and Ford Foundation President Darren Walker, who worked with Agnes Gund to establish an Art for Justice Fund that supports criminal justice reforms aimed at reducing mass incarceration.