MCAT Content / Perception / Bottom Up And Top Down Processing

Bottom-Up and Top-down Processing

Topic: Perception

Perception refers to the way sensory information is organized, interpreted, and consciously experienced and involves both bottom-up and top-down processing.

While our sensory receptors are constantly collecting information from the environment, it is ultimately how we interpret that information that affects how we interact with the world. Perception refers to the way sensory information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input. Bottom up processing is when sensory receptors pick up signals for the brain to integrate and process. An example of this is stubbing your toe on a chair, the pain receptors detect pain and send this information to the brain where it is processed. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts. This is called top-down processing. An example of this is if you see the chair you have stubbed your toe on before and you avoid it to make sure it does not happen again.

In top-down processing, there is always bias of environmental factors on a personal perception of the stimulus, this is known as context effect. Where cognitive psychology of a person’s environment affects their stimulus processing.

Look at the shape in Figure 1 below. Seen alone, your brain engages in bottom-up processing. There are two thick vertical lines and three thin horizontal lines. There is no context to give it a specific meaning, so there is no top-down processing involved.

Now, look at the same shape in two different contexts. Surrounded by sequential letters, your brain expects the shape to be a letter and to complete the sequence. In that context, you perceive the lines to form the shape of the letter “B.”

Surrounded by numbers, the same shape now looks like the number “13.”

When given a context, your perception is driven by your cognitive expectations. Now you are processing the shape in a top-down fashion.

One way to think of this concept is that sensation is a physical process, whereas perception is psychological. For example, upon walking into a kitchen and smelling the scent of baking cinnamon rolls, the sensation is the scent receptors detecting the odor of cinnamon, but the perception may be “Mmm, this smells like the bread Grandma used to bake when the family gathered for holidays.”

Although our perceptions are built from sensations, not all sensations result in perception. In fact, we often don’t perceive stimuli that remain relatively constant over prolonged periods of time. This is known as sensory adaptation. Imagine entering a classroom with an old analog clock. Upon first entering the room, you can hear the ticking of the clock; as you begin to engage in conversation with classmates or listen to your professor greet the class, you are no longer aware of the ticking. The clock is still ticking, and that information is still affecting sensory receptors of the auditory system. The fact that you no longer perceive the sound demonstrates sensory adaptation and shows that while closely associated, sensation and perception are different.

Practice Questions


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MCAT Official Prep (AAMC)

Section Bank P/S Section Passage 4 Question 29


Key Points

• Perception refers to the way sensory information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing. One way to think of this concept is that sensation is a physical process (bottom-up processing), whereas perception is psychological (top-down processing).

• Bottom-up processing refers to the fact that perceptions are built from sensory input. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts.

• Top-down processing refers to how we interpret sensations due to influences from our available knowledge, our experiences, and our thoughts.

• Although our perceptions are built from sensations, not all sensations result in perception. Due to sensory adaption, we often don’t perceive stimuli that remain relatively constant over prolonged periods of time.


Key Terms

perception: the organization, identification, and interpretation of sensory information

bottom-up processing: refers to the fact that perceptions are built from sensory input

top-down processing: refers to how we interpret sensations due to influences from our available knowledge, our experiences, and our thoughts



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