Conduction velocity groupings among axons of cat retinal ganglion cells, and their relationship to retinal topography.

Three unresolved issues in the conduction velocity groupings among the axons of cat retinal ganglion cells have been investigated. These are (i) the degree of separation of the velocity ranges of the axons of X-and W-type ganglion cells; (ii) the question whether the velocities of X-and Y-cell axons (i.e. of t1 and t2 axons have faster velocities than contralaterally projecting axons. Evidence is presented that the velocity ranges of W- and X-cell axons are almost completely separate; that the velocities of X- and Y-cell axons are not graded with retinal eccentricity (except in the immediate vicinity of the area centralis) and that ipsilaterally projecting axons are not faster conducting that contralaterally projecting axons. These results provide a context for summarising present understanding of conduction velocity groupings among the axons of cat retinal ganglion cells.