Effects of background and spatial pattern on incremental sensitivity of catfish horizontal cells.

Incremental sensitivity of cones and horizontal cells was examined in the retina of the channel catfish (Ictalurus punctatus). In horizontal cells, steady full-field background illumination made the spot-evoked dynamic response larger and faster. The "enhancement" of incremental sensitivity was maximal at background levels of 20-50 microW/cm2. Similar changes in response were obtained by enlarging the diameter of the test spot (to 4 mm) without background illumination. In cones, no such enhancement with background was observed and small (0.4 mm) and large (4.0 mm) spots produced similar responses. Similar enhancement by a steady background has been observed also in the proximal neurons of catfish retina.