Visual response properties of zebrafish tectal cells

The visual properties of zebrafish tectal cells have been studied with a variety of stimulation routines. These include illumination of the whole receptive field and of the surround, use of moving edges, very small spots, bars of varying orientations, moving spots with varying direction and speeds, growing discs, and pairs of spots whose presentation varies in position and sequence. A number of properties correlate with the classification scheme set forth in the preceding paper. Type B cells, unlike other types, are insensitive to moving stimuli. Experiments involving surround stimulation show that type S cells have inhibitory surrounds while those of type I do not. Type I cells, however, exhibit several properties which are consistent with an intratectal delayed inhibitory mechanism operating within the receptive field. These properties include the response to moving edges and growing stimuli, and the dependence of response duration on the size of a flashed stimulus. Various explanations of these properties are considered, and a specific model is proposed which states that cells of type I receive inhibitory input from neighbouring tectal cells of the same physiological type. The properties involved may be of direct importance in the visual behavior of the fish.