Abstract
Response properties of off-centre retinal ganglion cells (RGCs) were investigated in the cat by means of extracellular recordings. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. Response vs. log stimulus intensity functions were determined for the receptive field centres while both the test stimulus irradiance and the background illumination were varied over a range of up to 7 log units. In most off-centre cells, an increase in background illuminance produced a shift of the R-log I functions to higher irradiances of test stimuli indicating a normal desensitization of the centre response in the presence of background lights. In 20% of the off-centre cells, however, a strikingly different adaptation behaviour was observed. The receptive field centre became more sensitive in the presence of dim adapting backgrounds than in the dark adapted state. Accordingly, the threshold versus intensity function did not increase monotonically, but rather showed a ‘dip’ at dim backgrounds. The sensitization was observed only with a cone-stimulating test light in presence of a large, rod-adapting background. The sensitization disappeared when the background diameter was reduced to less than threefold the diameter of the receptive field. Sensitization could not be observed under any other chromatic conditions nor in on-centre cells.
Published Version
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