IS MINIMAL DIFFERENCE a major subject? Even so-called identicals, Marcel Duchamp observed, reveal shades of difference, which he memorably called infra-thin. Roni Horn’s work mines that proposition exhaustively, asking us to find differences in things and then to question why we need them. For Horn, the terrain of likeness—that which is similar, the same yet different, akin, or simply close—encompasses a panorama of experience. Her work dwells on differences of degree that, she suggests, constitute as profound a representational problem as the starker discrepancies that conventionally

Floating Coffins, 2009, the central work in “Currents of Time: New Work by Zineb Sedira,” presents footage of the rusting hulls of fishing vessels grounded off the coastline of Mauritania. The immense, fourteen-screen video installation occupied Iniva’s largest gallery, with eleven flat screens in three sizes congregating on the back wall of the darkened space and three screens placed on the side walls. Eight round speakers playing a single stereo sound track hung at varied heights overhead, inviting visitors to move about to obtain different perspectives on the imagery.

The saturated color