PERCEPTION OF FIRST-ORDER AND 2ND-ORDER MOTION - SEPARABLE NEUROLOGICAL MECHANISMS

An unresolved issue in visual motion perception is how distinct are th e processes underlying ''first-order'' and ''second-order'' motion. Th e former is defined by spatiotemporal variations of luminance and the latter by spatiotemporal variations in other image attributes, such as contrast or depth. Here we describe two neurological patients with fo cal unilateral lesions whose contrasting perceptual deficits on psycho physical tasks of ''first-order'' and ''second-order'' motion are rela ted to the maps of the human brain established by functional neuroimag ing and gross anatomical features. We used a relatively fine-grained n eocortical parcellation method applied to high-resolution MRI scans of the patients' brains to illustrate a subtle, yet highly specific diss ociation in the visual motion system in humans. Our results suggest th at the two motion systems are mediated by regionally separate mechanis ms from an early stage of cortical processing. (C) 1999 Wiley-Liss, In c.