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Top-down processing is also known as Conceptually-driven processing.

Bottom-up processing is also known as Perceptually-driven processing.

Conceptually-driven processing relies on information or previous knowledge that is brought to the situation and drives perception in a top-down manner. Oftentimes, this prior knowledge can impose structure onto what is perceived. Perceptually-driven processing is data-driven, and involves the perception of a stimulus by interpreting individual features in a bottom-up approach.

Context effects in the perception of words provides evidence for conceptual-driven processing. Subjects were presented with ambiguously drawn letters, such as a shape that looks similar to both an “H” and an “A.” When presented in different contexts, subjects perceive the letters to be the one that is most appropriate for that word. Between the letters “T” and “E,” subjects report the ambiguous shape to be an “H.” However, if presented between the letters “C” and “T,” it is perceived as an “A.” This occurs because people impose an interpretation on the stimulus based on their previous knowledge about the language. Conceptually-driven processing must have taken place during the perception of the ambiguous shape, since the physical properties of the shape were not enough to steer the proper categorization of the letter.

Frederic Bartlett discovered an interesting conceptually-driven process involving the reconstructive nature of the remembering and retelling of stories. When British readers attempted to recall a Native American story, "War of the Ghosts," they imposed a structure that had come from their own conceptual understanding of stories. They subconsciously excluded various elements and included others to make the story more compatible with their schematic concepts of a story. This top-down imposition of previous knowledge onto novel stimuli is evidence of conceptually-driven processing.

Still, these last two examples of conceptually-driven processing can only occur in conjunction with perceptually-driven processing. Data must be introduced to the system in order to experience or learn from the world. It is this dynamic relationship between perceptually-driven and conceptually-driven processing that allows for effective perception to occur.

The effects of perceptually-driven processing can be experienced while viewing visual displays that are fields of many repetitive distinctive physical features that carry or suggest little or no meaning. The perceptual system attempts to take in and organize the stimuli, resulting in illusions of motion or transitory grouping. With no previous knowledge to drive the perception of the data, perceptually-driven mechanisms take over and attempt to process the information.

I am often reminded of my own dynamic perceptual processing when meeting new people. While taking into account new information gleaned from listening to and watching a novel acquaintance, I also find myself imposing several characteristics onto his or her disposition that come from nowhere but my own conceptual framework. Beyond personality stereotyping, even a simple assumption (such as assuming that a fellow English speaker will be familiar with a particular idiom) requires some level of conceptually-driven imposition. Still, without perceptually-driven information, I would not have been able to deduce that the person is an English speaker to begin with. This phenomenon is known as transference.

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