Motion perception in optic neuropathy.

We tested motion perception in 15 eyes of 13 patients with optic neuropathy. Eleven of the eyes had optic neuritis. The motion perception paradigm tested subjects' ability to discriminate the direction of a global coherent motion signal amid varying levels of background noise. The results showed defective motion processing in eight of the 15 eyes. This defect was not due to low visibility (poor spatial resolution), since 11 of the 15 eyes had Snellen acuities of 20/20 or better. Neither was impaired motion perception due to decreased luminance sensitivity, since attenuating the display signal by 2.1 log units (0.6 units more than the worst relative afferent pupillary defect in any patient) in five normal eyes had no effect. Motion perception and critical flicker fusion were independent of each other. Given proposals that both depend exclusively on the same M, or transient, channel, we had not predicted this double dissociation between flicker and motion perception.