The internal horizontal cell of the frog: spatial summation.

The receptive field properties of internal horizontal cells (IHCs) were studied in the frog Rana pipiens. The space constant of each cell was determined by the use of stimulus spots of various sizes or by moving a light slit across the retina, varied from 100-500 microns by the former and 100-720 microns by the latter method. A similar range of values has been reported for Xenopus although its IHCs are much larger than the IHCs of Rana. Apparently, coupling among the IHCs is more efficient in the latter than in the former retina. The large range in values suggests substantial variation in coupling efficiency among cells of the same retina.