Spatial summation of cone mechanisms in goldfish

Experiments were performed to evaluate the spatial summation areas of the u.v.-, blue-, green- and red-sensitive cone mechanisms of goldfish. All the cone mechanisms were in compliance of Ricco's law, summing target radiance linearly over a certain range of target diameters with an average slope of 2.4. The critical diameters of the blue-, green- and red-sensitive cone mechanisms were all close to 6 deg. However, the critical diameter for the u.v.-sensitive cone mechanism was 8.0 deg, clearly different form than other cone mechanisms. The observation that the u.v.-sensitive cone mechanism has a larger spatial summation area suggests that u.v.-sensitive ganglion cells may have larger receptive field centers.