bottom-up processing

Meaning: Bottom-up processing is data-driven perception. Receptors detect basic features of a stimulus, such as edges, orientation, color and motion, and the brain assembles them step by step into a recognized object or pattern. Feature detection by neurons in the visual cortex is the standard example. Information flows from the sensory input toward higher cortical areas, so the percept is built mainly from the stimulus itself rather than from expectation.

On the MCAT: Passages contrast it with top-down (conceptually driven) processing, which uses prior knowledge, expectations and context. If a person views an unfamiliar object or a meaningless pattern and must rely on its features, the answer is bottom-up. If context lets someone read a smudged word or resolve an ambiguous figure, the answer is top-down. Bottom-up processing tends to dominate when the stimulus is novel and the viewer has little relevant knowledge. It also connects to feature detection and parallel processing.

Common confusion: Students equate bottom-up processing with sensation. Sensation is the detection of physical energy by receptors; bottom-up processing is a way of organizing that input into perception. Another mistake is to treat the two directions as rival accounts. Most everyday perception combines both, and context effects and perceptual illusions show top-down influence on what the bottom-up input produces.