We assessed the variety of spiking patterns produced by retinal ganglion cells in response to repeated presentations of natural scenes. Ganglion cells from isolated retinae of larval tiger salamanders and rabbits were recorded extracellularly with a multi-electrode array. Natural movies were videotaped with a Camcorder, displayed using a Macintosh computer and monitor, and projected onto the retina. Movies were taken of woodland and river scenes in the daytime with the camera mounted on a tripod and occasionally panned slowly. Under stimulation from three different 30-s natural movie clips, ganglion cells in both the salamander and rabbit responded with discrete, highly precise episodes of firing separated by intervals of complete silence. These firing events had rapid onsets, high peak firing rates, and highly reproducible spike counts. Such patterns of firing shared many qualitative similarities with those found under random flicker stimulation, a simpler stimulus ensemble. A notable difference, however, was the greater variety of time courses for firing events under natural stimulation. Maybe one can tailor synthetic stimuli to match various statistical properties of Nature and reproduce the observed variety of firing patterns. Such stimuli would provide a useful testbed for the stimulus-response relationship under natural conditions.
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