Top-down processing, also referred to as conceptually-driven processing or knowledge-driven processing, refers to “processing that begins by considering the effect of the knowledge a person brings to the perceptual situation” (Goldstein, 2002, p. 8). As such, this kind of processing begins with cognitive information at the higher levels of the brain and is heavily influenced by the beliefs, memories and expectations that the observer brings to the situation. In contrast, “processing that begins with the information received by the receptors” is known as bottom-up processing or data-driven processing (p. 8). This type of processing involves the sensory receptors registering physical stimulus from the environment and sending it to the brain for integration and cognitive processing. Human perception entails the interaction of both processes working together in order to make sense of the environment.
This top-down processing, which depends upon a person’s knowledge of the context provided by a particular scene, can influence perception of new stimuli, especially that which appears similar to the previously interpreted content. In this way, top-down processing increases the efficiency of the sensory system by using the previously gained knowledge to influence incoming information (Goldstein, 2002; Matlin, 2002). For example, it is reasonable to expect certain events based on what has happened before in similar contexts, or based on what has been previously learned about a particular situation.
In some cases, however, these interpretive shortcuts can lead to errors in perception. Often particular stimuli are recalled that are not present in a given scenario, merely on the strength of the expectation (i.e., the top down processing) that they would be there (Matlin, 2002). Thus, when relying on the familiar experience of the routine bus stop, a new aspect, such as the new company name, may be overlooked or even inaccurately recalled based upon the assumptions that this experience of the event will be like all others before it.
Furthermore, top-down processing often comes into play in the process of interpreting ambiguous information being received from the senses - for example, viewing an item that is blurry, obstructed, distorted, at an unusual angle, or in some other way unclear, incomplete, and ambiguous. Through top-down processing one uses context, the information surrounding an ambiguous stimulus, to help figure out exactly what meaning to assign to unclear information.
Figure 1 represents a simplified example of how top-down processing and assumptions based on context can influence, and in some cases distort interpretation of a stimuli.
Figure 1: Stimuli in Different Contexts
In this example, the middle symbol in each set provides exactly the same visual information. However, this information can be interpreted in more than one way. Since it is typically the case that information coming into the senses usually appropriately matches its surroundings, relying on context represents a helpful shortcut for the brain when unclear or novel stimulus is encountered.
Thus, when are faced with an ambiguous or seemingly contradictory bit of information from the environment, one uses what is already known to help interpret it - sometimes even developing an idea of what will be experienced even before it is actually seen, heard, smelled, tasted or felt - based primarily on prior knowledge and experiences. Interpretations often depend upon hints in the environment and what those hints led the perceiver to expect - as in Figure 1 or in the above scenario. These expectations aid in figuring out what we are sensing in ambiguous situations.
In contrast, if an experience or stimulus were to be mentally processed completely through bottom-up processing, the conclusions would be somewhat different. In this case, each aspect of sensory information would be evaluated on its own merits, so to speak. The interpretation of the situation would be determined entirely by the incoming stimulus information itself, not in relation to memory, previous experience or expectation. Thus, the recognition would take longer as one would not be skipping steps or accessing already previously processed sensory information to use as interpretative clues. However, the stimulus would be more specifically attended to and fully processed, rather than being absorbed in the familiar context. Thus, the chances that the interpretation would be more accurate are significantly higher.
Typically, human perception represents an interdependent best compromise between these two types of processing. Thus, reality is partially influenced by bottom-up processing, where signals travel from lower levels into higher areas of the brain and partially by top-down processing where stored experiences and expectations modify incoming signals. These processes smoothly and continually work in concert to help individuals quickly and relatively accurately understand the vast array of stimuli encountered each day.
Bernstein, D. A., Penner, L. A., Clarke-Stewart, A. & Roy, E. J. (2002). Psychology (6th ed.). New York, NY: Houghton-Mifflin.
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