Spatial scale and cellular substrate of contrast adaptation by retinal ganglion cells

Human visual perception and many visual system neurons adapt to the luminan ce and contrast of the stimulus. Here we describe a form of contrast adapta tion that occurs in the retina. This adaptation had a local scale smaller t han the dendritic or receptive fields of single ganglion cells and was inse nsitive to pharmacological manipulation of amacrine cell function. These re sults implicate the bipolar cell pathway as a site of contrast adaptation. The time required for contrast adaptation varied with stimulus size, rangin g from approximately 100 ms for the smallest stimuli, to seconds for stimul i the size of the receptive field. The differing scales and time courses of these effects suggest that:multiple types of contrast adaptation are used in viewing natural scenes.