A<unk>  is a means of extracting information from a<unk>  scene. In his studies on human<unk>  cognition, Shimon Ullman proposed that the human<unk>  system's task of perceiving shape properties and spatial relations is split into two successive stages: an early "bottom-up" state during which base representations are generated from the<unk>  input, and a later "top-down" stage during which high-level primitives dubbed<unk> s" extract the desired information from the base representations. In humans, the base representations generated during the bottom-up stage correspond to retinotopic maps (more than 15 of which exist in the cortex) for properties like color, edge orientation, speed of motion, and direction of motion. These base representations rely on fixed operations performed uniformly over the entire field of<unk>  input, and do not make use of object-specific knowledge, task-specific knowledge, or other higher-level information.
The<unk> s proposed by Ullman are high-level primitives which parse the structure of a scene, extracting spatial information from the base representations. These<unk> s are composed of a sequence of elementary<unk>  operators specific to the task at hand.<unk> s differ from the fixed operations of the base representations in that they are not applied uniformly over the entire<unk>  field --- rather, they are only applied to objects or areas specified by the<unk> s. Ullman lists the following as examples of<unk>  operators: shifting the processing focus, indexing a salient item for further processing, spreading activation over an area delimited by boundaries, tracing boundaries, and marking a location or object for future reference. When combined into<unk> s, these elementary operators can be used to perform relatively sophisticated spatial tasks such as counting the number of objects satisfying a certain property, or recognizing a complex shape.
A number of researchers have implemented<unk> s for processing camera images, to perform tasks like determining the object a human in the camera image is pointing at. Researchers have also applied the<unk> s approach to artificial map representations, for playing real-time 2D video games. In those cases, however, the map of the video game was provided directly, alleviating the need to deal with real-world perceptual tasks like object recognition and occlusion compensation.
Visual routine
Mental status examination
Eyeglass prescription
Prenatal care
Birth control
Cognitive neuropsychiatry
Diabetology
Hearing impairment screening