Gating, selectivity and blockage of single channels activated by cyclic GMP in retinal rods of the tiger salamander.

1. Patches in the inside-out configuration were excised from the membrane of outer and inner segments of the larval tiger salamander, Ambystoma tigrinum. The current flowing through single channels opened by cyclic GMP was studied with the voltage clamp technique.

Different channel-gating properties of two classes of cyclic GMP-activated channel in vertebrate photoreceptors.

We report that two types of cGMP-activated channel coexist in the photoreceptor plasma membrane, with the most commonly encountered class appearing broadly similar to the channel reported in previous patch-pipette experiments. However, we find that flickering of this channel between the open and closed states is so rapid that a discrete single-channel conductance cannot unequivocally be resolved; the occurrence of flickering is largely independent of membrane voltage and of the presence of cytoplasmic Ca2+ or Mg2+. In recordings from the inner segment we occasionally find a second class of cGMP-gated channel, with activity resembling that reported for cloned channels.

Computational aspects of motion perception in natural and artificial vision systems.

In this paper a computational scheme for motion perception in artificial and natural vision systems is described. The scheme is motivated by a mathematical analysis in which first-order spatial properties of optical flow, such as singular points and elementary components of optical flow, are shown to be salient features for the computation and analysis of visual motion. The fact that different methods for the computation of optical flow produce similar results is explained in terms of the simple spatial structure of the image motion of rigid bodies.