Global motion mechanisms compensate local motion deficits in a patient with a bilateral occipital lobe lesion.
Successive stages of cortical processing encode increasingly more complex types of information. In the visual motion system this increasing complexity, complemented by an increase in spatial summation, has proven effective in characterizing the mechanisms mediating visual perception. Here we report psychophysical results from a motion-impaired stroke patient, WB, whose pattern of deficits over time reveals a systematic shift in spatial scale for processing speed. We show that following loss in sensitivity to low-level motion direction WB's representation of speed shifts to larger spatial scales, consistent with recruitment of intact high-level mechanisms. With the recovery of low-level motion processing WB's representation of speed shifts back to small spatial scales. These results support the recruitment of high-level visual mechanisms in cases where lower-level function is impaired and suggest that, as an experimental paradigm, spatial summation may provide an important avenue for investigating functional recovery in patients following damage to visually responsive cortex.
Beardsley
Scott A
SA
Department of Biomedical Engineering, Marquette University, Milwaukee, WI, USA.
Vaina
Lucia M
LM