Bottom-up processing begins with a real-time stimulus, like a loud horn blast or the smell of coffee, which leads to analysis.

Have you ever wondered how your brain senses, perceives, and interprets incoming data?

One way we make sense of the world is with a psychological strategy called “bottom-up” processing.

This strategy begins outside of us — with external data like a cool breeze, a flickering light, or a car whizzing by. Then this sensory information travels up to your brain where it gets analyzed.

“Bottom-up” processing is a psychological strategy first defined in the 1960s by American psychologist James J Gibson. This process is considered one of the core ways we understand the world around us.

It’s called “bottom-up” because it begins with the external stimulus — such as a tree or the smell of cookies — and then that sensory information moves to the brain for analysis.

For instance, if you suddenly detect a sweet chocolaty smell wafting through the house, you might then determine that someone in your home is baking chocolate chip cookies.

To determine this, you didn’t need any other context or information — you simply used the sweet smell (the stimulus or raw data) to make your analysis. Your perception didn’t require prior knowledge that anyone was baking cookies.

Overall, bottom-up processing involves the following steps:

  • intake of new sensory information
  • sensory receptors send signals to the brain
  • the brain creates a perception via these signals

A few years after the concept of bottom-up processing emerged, British psychologist Richard Gregory proposed “top-down” processing as bottom-up’s counterpart. The two theories are typically taught side-by-side.

For many years, research on bottom-up and top-down processes have been conducted separately. However, in the real world, these two strategies dynamically interact to help us understand the world around us.

Bottom-up is a reductionist theory, meaning it starts by observing a concept’s most basic parts. The opposite of reductionism is holism theory, which is the theory for “top-down” processing.

In top-down processing, the brain uses hypotheses or theories to fill in the blanks. So while bottom-up processing relies on sensory data alone, top-down begins with the whole picture. It also relies on context, previous knowledge, and your expectations.

For instance, have you ever read a paragraph where every word is spelled completely wrong, but you can easily read what it says? While the individual words look like nonsense, you can use the larger context to figure them out. This is top-down processing.

Here are the key differences between the two strategies:

  • Bottom-up processing: begins with the stimulus, travels through the senses, and works upward toward the brain where it’s analyzed.
  • Top-down processing: is holistic and stems from the big picture. It uses context clues, past experiences, expectations, and prior knowledge to come to an analysis.

Research shows that the two processes are controlled by different brain networks. The bottom-up system uses the ventral frontoparietal network, while the top-down system uses the dorsal frontoparietal network. We use both strategies throughout the day.

It’s raining!

You’re running out the door to meet a friend for lunch. As you walk to your car, a brisk breeze hits your face. The sky is dark, and you hear thunder. You’d better grab an umbrella!

In this case, your senses detected a dark sky, thunder, and wind. You made a quick analysis that it was going to rain and that you should grab an umbrella.

B or 13?

“B or 13?” is a commonly used example to demonstrate the difference between bottom-up and top-down processing styles.

Let’s say that there are two markings on a page. One is a straight up-and-down line and the other is a line that’s curved twice, like two stacked half-circles. There’s very little space between the two figures.

With bottom-up processing, you might assume it’s a B right away. You see that the shape looks like how you expect a B to appear so you assume it’s a B.

However, if the markings are flanked by a 12 on the left and a 14 on the right, you might assume the marking is a 13. This would be using top-down processing because the brain used contextual clues to determine whether the shape is a B or 13.

Prosopagnosia (face blindness)

Prosopagnosia, or face blindness, is a neurological disorder, characterized by an inability to recognize familiar faces. In some cases, people with prosopagnosia cannot recognize their own faces.

Face blindness is a demonstration of bottom-up processing. People with this disorder can observe facial characteristics, such as brown eyes or a small nose, and know it’s a “face.” But they can’t identify who it belongs to because they lack the ability to perform top-down processing.

Oliver Sacks, a British neurologist well-known for his successful treatment of people with “sleeping sickness,” lived with prosopagnosia.

“Sensation” is the bottom-up process by which our senses — vision, hearing, smell, touch, and taste — receive and relay external stimuli.

“Perception” is the top-down mechanism that our brains use to organize and interpret data, which we put into context.

In bottom-up processing, sensation and perception are essentially the same. In other words, we perceive items via sensation — rather than with our conceptual ideas.

In top-down processing, perception and sensation are separate. First, we use context and expectations to create a holistic perception of the world, and then we start to focus on the smaller details using sensation.

We use both bottom-up and top-down processing every day to understand the world around us.

Bottom-up is a real-time processing strategy that allows you to understand your immediate surroundings. Without any prior expectations or context, you can quickly perceive what’s right in front of you — like a rain cloud or a speeding car — and then analyze it so you can make appropriate decisions.

We then use top-down processing to add in the contextual clues, giving us a more accurate picture of what we are experiencing. Both types of processing are important and are used side-by-side.