Motion Seeing something moving Cormack 323 Lecture 14 How fundamental is motion? • in my opinion, it is the second most basic function (behind phototropism) a visual system can perform • an example… Why we need motion sensitivity: • predators move • mates move • food moves motion can break camouflage motion can define form Why we need motion sensitivity: • • • • predators move mates move food moves we move Four types of image motion produced by our own motion: • • • • rotation (prob. least important) radial expansion translation parallax Radial Expansion 1. 2. Radial Expansion (looking out the windshield) Translation 1. 2. Translation (looking out the side window) Motion Parallax 1. 2. expansion + translation + parallax = “optic flow” Optic Flow • Gives us info about our motion • Gives us info about environment • but, unfortunately, we can also move our eyes, creating more motion vectors… What if we moved and made an eye movement? •answer: the vectors sum head-totail vector from eye movement resultant vector (motion + eye movement) vector from motion Translation + eye movement Motion Parallax just driving by... just making an eye or both. movement... The problem with eye (or head) movements bus the visual field bus window stationary eye looking at stationary bus with moving person same moving person, but -did the bus move? -did the eye move? -did both move? How does the nervous system encode motion? What makes a Motion Receptive Field? Answer: a surprisingly simple neural circuit called a “Reichardt detector” simple summing neuron Reichardt detector Reichardt detectors in space-time. excitatory inhibitory time space a little scallop Reichardt detector excitatory inhibitory time space a scallop Reichardt detector and moving edges time space Summary • • • • • kinds of retinal motion motion as an environmental (depth) cue motion and eye movements real and apparent motion receptive fields for motion (Reichardt detectors) • the power of motion in evolution • a last look look at motion parallax... Stereoscopic depth perception: motion parallax without having to move. The Conceptual Equivalence of 3 Judgments of Spatial Offset.