What is meant by bottom-up and top-down processing in sense and perception?

Bottom-up processing is the analysis that begins with the sense receptors and works up to the brain's integration of sensory information. It describes the work of sensory receptors that change stimuli into neural messages that most usually reaches the brain. Sensation is the process by which our sensory receptors and nervous system receives stimulus energies from our environment. Bottom-up processing is akin to sensation. An example of bottom up processing occurs in vision. Bottom-up processing …

…top-down processing in vision is vivid in the Gestalt ideas of grouping. Grouping is the perceptual tendency to organize stimuli into coherent groups. This is an example of top-down processing, as it incorporates what we expect in our perception of an image. The various tendencies that our brain has are proximity, similarity, continuity, closure and connectedness. Using the rules of closure, we would interpret particularly arranged dashed-lines as a whole triangle, rather than singular lines.