Turtle and catfish horizontal cells show different dynamic response.

Horizontal cell responses of catfish and turtle have been found to differ in a characteristic way. These characteristics established by white-noise analysis show that the impulse response (first order Wiener kernel) of the catfish horizontal cell has a substantially shorter latency as well as peak response time than that of the turtle. The turtle horizontal cell, on the other hand, has a dynamic gain which is twice that of the catfish. Since these differences were established under conditions of ambient illumination, they may be expected to be functionally important in the visual experience of the animals under normal environmental conditions.