Figure 2.

Functional organization of ON-OFF PACs, ON parasol and OFF parasol cells. A–C, Reverse correlation of spike trains of each cell with a white noise stimulus revealed the spatial receptive field of each cell (see Materials and Methods). Gaussian fits to receptive fields of recorded cells are shown as ellipses, accumulated for each cell type separately, and superimposed on the outline of the 512-electrode array (1890 × 900 μm). The receptive fields of each cell type formed a regular mosaic tiling the region of retina recorded. D–F, Time course of reverse correlation at the receptive field center is shown for all cells of each type superimposed, and for each of the three display primaries (red, green, and blue). These time courses reveal biphasic integration over time before spike (i.e., biphasic impulse responses). G–I, Autocorrelation of spike trains of different cell types were obtained during white noise stimulation, and are shown superimposed for all cells of each type. Each trace shows, for one cell, the normalized spike rate as a function of time after the occurrence of a spike. The characteristic waveforms for cells of each type reveal homogeneous spike train dynamics (Devries and Baylor, 1997).