(A) A stand of aspen trees, seen from a distance, presents primarily vertical lines (Image credit: John Price). (B) Closer inspection reveals primarily horizontal features in the bark of individual trees (Image credit: Peng Chen). (C) Simplified schematic of the retinal circuitry showing the synapses between photoreceptors (top) and bipolar cells, and between bipolar cells and a single ganglion cell. The amacrine cells influence the behavior of the bipolar cells (and the ganglion cells). (D) Neurotransmitter release by bipolar cells (y-axis) versus the membrane potential of these cells. Bipolar cells inhabit one of three release regimes: quiescent (blue), when visual stimulation is insufficient to evoke release; linear (red), when release is proportional to the stimulus; and rectified (gold), when only positive stimuli evoke release. (E) Schematic showing a checkerboard stimulus presented to a 2 × 2 array of bipolar cells. (F) The change in the membrane potential (y-axis) over time (x-axis) of each bipolar cell depends on whether it receives a positive stimulus (2 and 3) or a negative stimulus (1 and 4) from the checkerboard. (G) The release of neurotransmitters from the four bipolar cells and the resulting response in the ganglion cell (bottom) depend on the release regime occupied by the bipolar cell (see main text).