The first investigator to use this methodology to study the visual system, Haldan Keffer Hartline, found that some ganglion cells in the retina of a frog were activated by the onset of a spot of light, others by the offset of the light, and still others responded to both the onset and the offset of the light. As you might surmise, Hartline called the first group on ganglion cells, the second group off ganglion cells, and the third group on-off ganglion cells.

Continuing with this line of research, Stephen Kuffler (e. g., Kuffler, 1953) used microelectrodes to record the activity of single ganglion cells in the optic nerve of a cat. He found that the receptive fields of the cells resembled concentric circles, with either an “on” center and an “off” surround, or vice-versa. These types of cells are called either center-on, surround-off ganglion cells or center-off, surround-on ganglion cells. When a light is shined in the center of its receptive field, the center-on, surround-off ganglion cell responds with an increase in its firing rate; light in the surround inhibits the cell's firing. Just the opposite happens with the center-off, surround-on ganglion cell; light in the center inhibits the cell's firing, whereas light in the surround causes increased firing.

Kuffler and others who have studied these cells have found that the size of the receptive fields depends on the retinal location of the ganglion cells being studied. In general, ganglion cells from the central part of the retina have smaller receptive fields than ganglion cells in the peripheral retinal regions. What does this suggest to you about which receptor cells (rods or cones) are connected to the ganglion cells?