Independent first and second-order motion energy analyses of optic flow

The human visual system contains a functional sub-system that is specialize d to extract image motion. The sensitivities of neurons change as one moves higher in the pathway. Initially cells collect responses from small retina l areas but later those local signals are combined to extract global motion either frontoparallel or radial motion relative to the center of the visua l field. This sequence of processing is conducted in parallel by pathways s ensitive to the motion of either the first- or second-order luminance stati stics of the image. Previously it had been shown that these two pathways we re independent at the level at which local motion signals and frontoparalle l global motion signals are extracted. In this study independence is tested during the extraction of radial global motion; a process strongly associat ed with cortical area MST (or V6) and the next logical level in the motion pathway. We find that the two pathways do provide independent estimates of radial motion and are? therefore, independent at all levels of the motion p athway that have been tested to date.