Abstract
Multiple cues provide information about the depth structure of objects: disparity, motion and shading and texture. Functional imaging studies in humans have been preformed to localize the regions involved in extracting depth structure from these four cues. In all these studies extensive controls were used to obtain activation sites specific for depth structure. Depth structure from motion, stereo and texture activates regions in both parietal and ventral cortex, but shading only activates a ventral region. For stereo and motion the balance between dorsal and ventral activation depends on the type of stimulus: boundaries versus surfaces. In monkey results are similar to those obtained in humans except that motion is a weaker cue in monkey parietal cortex. At the single cell level neurons are selective for gradients of speed, disparity and texture. Neurons selective for first and second order gradients of disparity will be discussed by P Janssen. I will concentrate on neurons selective for speed gradients and review recent data indicating that a majority of FST neurons is selective for second order speed gradients.