direction of their travel randomly from frame to frame (Watamaniuk, 1995). Thornton and Gilden (2001) use an additional technique of using motion transformations and smoothing on randomly colored black and white dots to create a percept of coherent motion within apertures of similar motion noise.Global Motion Sometimes motion is perceived with very little cognitive effort, as is the case for trajectory motion and optic flow. Other kinds of motion require more cognitive effort in order to be processed accurately like rotation. By studying the differences in the way motion is processed, researchers are able to infer the role of attention in the motion system. Thorton and Gilden (2001) examined the differences in processing of three types of motion: homogeneous flow (translation), rotation (or curl) and divergence (contraction and expansion). These types of motion belong to a category of motion known as optic flow. Optic flow is motion created as a result of the observers movement in relation to his or her environment and can be considered as simple or complex. Translation is optic flow in a single linear direction much like what you might see while looking out of the side window of a car, and would be considered simple in terms of computation. Both rotation and divergence flows are considered computationally complex because the direction of flow is based on relative spatial location across time or how one part of the scene moves in relation to another part of the scene. This is what they consider image-based. Translation is considered computationally simple because the direction of flow can be determined by examining any single portion of the scene. This is referred to as scene-based because it does not depend on movement in relation to any one element or image within the scene. Reichardt detectors are tuned to displacement overtime and to specific directions. While this is well suited to detecting linear motion, it is insuff...
