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Movement Perception

In recent years two pathways carrying visual information have been identified: the P and the M systems. The first is connected with parvocellular cortical areas, where high spatial frequency stimuli are elaborated, that is, where visual resolution takes place. The second system is connected with the magnocellular cortical area, concerned with movement perception where low spatial frequency stimuli are evaluated. A dissociation between P and M systems takes place in amblyopia, with deficits involving mainly the P system, while the M system performance has actually been described as better than that deriving from the P system.135

Speaking of movement perception, it is possible to evaluate the smallest movement of a given stimulus that gives rise to the perception of movement by means of the oscillatory movement displacement threshold (OMDT). OMDTs fall into the category of hyperacuities. Kelly and Burckingham244 found no OMDT deficits in amblyopes with stereopsis but elevated OMDT in amblyopia without stereopsis. These authors showed also that whereas OMDTs improve with age in normals, the thresholds of the dominant eye of amblyopes without stereopsis do not. This finding could be due to an occlusion treatment performed earlier, but no evidence was found for this. The alternative theory suggests the existence of deficits in the dominant eye. Donahue and coworkers120 evaluated motion detection abnormalities in patients with anisometropic amblyopia and found abnormalities in motion detection that extend into the midperiphery of the visual field. Motion detection is altered also in optic nerve disorders and open angle glaucoma. The significance of these results needs still to be established.

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