Cover legend: Retinal ganglion cells (white) are electrically stimulated using a multielectrode array (black circles). The nine color contours represent the spatial extent of electrical signals produced by each neuron (largest signal in red). Ganglion cells and their axons were labeled using a fluorescent retrograde tracer injected into the optic nerve. For more information, see the article by Sekirnjak et al. in this issue (pages 4446–4456).