Overview of salamander ganglion cell responses to natural images.
A) Schematic of the sequence of 300 natural images presented individually in a pseudo-random fashion for 200 ms each, with an inter-stimulus-interval of 800 ms. B) Left: One of the 300 natural images, overlaid with the 3-sigma outline of the receptive field of a sample retinal ganglion cell. Right: Raster plot of spike times recorded from the sample cell for 13 repeated presentations of this image. Every row corresponds to one image presentation. At the bottom, the timeline of stimulus presentation is shown, indicating the 200-ms presentation time, surrounded by periods of gray illumination. The vertical gray line at 300 ms marks the end of the applied window for counting spike numbers. C) Spike count variance (y-axis) vs. average spike count (x-axis) from the sample cell for each of the 300 images. The gray line denotes the expected relation of variance and average spike count for a Poisson process. Inset: Histogram of Fano factors for each image, excluding those with zero spikes. D) Average over images of the single-image spike count variance as a measure of response noise (y-axis) vs. the average spike count over all images as a measure of typical signal size (x-axis), shown for each recorded cell. Inset: Histogram of Fano factors for each cell, averaged over images. N = 156 cells from 9 retinas. E) Average over images of the single-image spike count variance as a measure of response noise (y-axis) vs. variance over images of the average spike count per image as a measure of response range (x-axis), shown for each recorded cell. The sample cell is marked in red in D and E.