Spatial organizations of catfish retinal neurons. II. Circular stimulus.

1. Temporal dynamics of receptive-field components were identified by use of circular stimuli whose diameter was modulated in white-noise fashion. 2. A thin ring of light evoked a complex response from the horizontal-cell soma but not from its axon. 3. All bipolar cells had a biphasic receptive field whose incremental sensitivities were comparable for the field's center and surround. 4. Type-N cells had a biphasic field whose two components were segregated both in time and space. 5. Type-C cells showed nonlinearities, which did not depend on the types of light inputs and which were intrinsic to the cell. 6. Ganglion cells could be classified roughly into two classes: small- and large-field cells. Their main nonlinearity was rectification. 7. Our studies on the catfish retna have shown that the distal cells are essentially linear in time and space and can be identified functionally by any type of input. The proximal cells, however, have a complex functional repertoire whose identification poses considerable difficulty.