... what a person expects, or has experienced before, it is referred to as "top-down" influence (sometimes referred to as indirect perception). Lower level, so called "bottom-up" or "data driven" processing, refers to processing that begins "at the bottom" with raw sensory data that feed "up" to the brain. A bottom-up explanation of visual perception argues that the brain forms perceptions by combining the responses of multiple feature detectors in the primary cortex, which themselves integrate input from neurons lower in the visual system. It involves the analysis of individual elements of the stimulus and works up to the brains integration of them into a unified perception. In contrast top down processing (also known as concept driven processing) is the perceptual processing in which existing knowledge, concepts, ideas or expectations are applied in order to make sense of incoming stimuli. Top down processing starts at the top, from the observer's ...

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