Figure 1.
White noise visual stimulation. A, The average stimulus observed 50 ms before a spike in two primate retinal ganglion cells in one retina. Dots represent the location of each electrode in the 61-electrode array. The primary (recording) electrode is marked with a circle, the site of electrical stimulation with a radiating symbol. Lighter-than-background pixels describe the receptive field of an ON parasol cell (left), whereas the region of darker pixels indicates the receptive field of an OFF parasol cell (right). Scale bar, 65 μm. B, Average time course of STA (spike-triggered average) contrast of the red, green, and blue display phosphors in the 300 ms preceding a spike, summed over several pixels in the center of the receptive field (same cells as in A). Black dashed line shows the best-fit curve to the green signal (Chichilnisky and Kalmar, 2002). The ON cell (left) shows a dominant positive lobe whereas the OFF cell (right) exhibits a dominant negative peak. C, Receptive fields of nine ON parasol ganglion cells and 13 OFF parasol ganglion cells recorded simultaneously in this retina. Ellipses represent 1 SD of the Gaussian fit to the spatial profile of each receptive field. The shaded fields indicate cells electrically stimulated in this retina. The small circles mark the cells shown in the above panels (same scale as in A). D, Electrical images of two ON and two OFF cells in this retina. Colored lines represent the interpolated amplitudes of the electrical signal measured at all nearby electrodes, normalized to the largest spike signal. Black ellipses are 1 SD of the Gaussian fits to the amplitude data and were used to describe the electrical image size of each cell (same scale as in A).