What's the differences between top-down and bottom-up processing?

Answer 1

in top down processing we are using previous knowledge in order to interpret in-coming perceptions. Top-down processing models emphasize the varying degrees to which incoming sensory information is shaped, selected, and influenced by context, expectations, and prior learning. Since very little (if any) sensation occurs in the absence of context, expectations and at least some degree of past experience, top-down processing is an aspect of every act of perception. However, in some cases, top-down processing may more heavily influence the perceptual experience than others.

Bottom-up processing approaches emphasize incoming sensory stimuli and the operations performed on them to build up to a meaningful perceptual representation. The suggestion is that processing is mostly uni-directional, from the sensory to the final perceptual interpretation, each stage adding something to the next. The three major models of bottom-up processing are template-matching theory, featural-analysis theory, and prototype-matching theory.