Top-down processing is a cognitive process in which the brain makes inferences about new or unfamiliar information based upon the context in which the information is used and past experience. It is a process by which the brain looks at the whole rather than the individual parts to derive meaning. In top-down processing, only after the overall concept is understood does the brain begin to focus on details.
Though top-down processing can be useful, it does have some problems. Top-down processing can be influenced by what a person expects to observe. If a person is reading a list of colors, changing the font color to a contrasting color slows down the speed at which the person is able to read the word list. Placing unfamiliar words in a list of familiar words that are connected by a theme may automatically make a person associate the meaning of the new words with the theme of the others, even though the new words may belong in an entirely different category.
In contrast, bottom-up processing involves the piecing together of details to develop an understanding of the whole. The focus is on individual pieces of data, which are scrutinized for ways to link them together. Linking together these individual pieces of data eventually results in a total picture.