BROAD TUNING FOR SPATIAL-FREQUENCY OF NEURAL MECHANISMS UNDERLYING VISUAL-PERCEPTION OF COHERENT MOTION

NEURAL events underlying perception of coherent motion are generally b elieved to be hierarchical(1,2): information about local motion is reg istered by spatio-temporal coincidence detectors(3-5) whose outputs ar e cooperatively integrated at a subsequent stage(6,7). There is disagr eement, however, concerning the spatial scale of the neural filters un derlying these operations. According to one class of models, motion re gistration is initially accomplished in parallel at multiple spatial s cales(3-5), with filters tuned to lower spatial frequencies responsive to larger motion displacements than filters tuned to higher frequenci es. According to another scheme, motion analysis involves a single, br oadly tuned spatial filter, with optimal displacement dependent on spa cing of local elements(8). Here we use a masking procedure to measure the extent to which dynamic noise depicted at one spatial scale interf eres with detection of coherent motion conveyed by image features at a nother spatial scale. Our results indicate that a single filter, broad ly tuned for spatial frequency, is mediating detection of coherent mot ion. This finding dovetails with known physiological properties of neu rons at an intermediate stage of motion processing.