Sensation and Perception: Learn it 2—What is Perception?

Perception and Processing

While our sensory receptors are constantly collecting information from the environment, it’s how we interpret that information that shapes the way we experience and interact with the world.

perception and processing

Perception refers to the way sensory information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing (Egeth & Yantis, 1997; Fine & Minnery, 2009; Yantis & Egeth, 1999):

  • Bottom-up processing refers to sensory information coming in from a stimulus in the environment that then drives you to think about it and interpret it (senses, then thought).
  • Top-down processing refers to knowledge and expectancy driving a process, meaning that you first think about and interpret a sensation (thought, then senses).

Bottom-up versus top-down 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.

text or image of a thick vertical line and three thin horizontal lines, then another thick vertical line.
Figure 1. What is this image? Without any context, you must use bottom-up processing.

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.”

The letter A, then the same shape from before that now appears to be a B, then followed by the letter C.
Figure 2. With top-down processing, you use context to give meaning to this image.

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

The number 12, then the same shape from before that now appears to be a 13, then followed by the number 14.
Figure 3. With top-down processing, you use context to give meaning to this image.

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

Sensation vs. Perception

A helpful way to distinguish between the two:

  • Sensation is physical—it’s the raw detection of sensory input.
  • Perception is psychological—it’s the interpretation and meaning we attach to those inputs.

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.”

When Sensation Fades: Sensory Adaptation

Although our perceptions are built from sensations, not all sensations result in perception. For example, some sensations are not perceived due to sensory adaptation.

sensory adaptation

Sensory adaptation is the loss of perception of stimuli that remain relatively constant over prolonged periods of time.

Imagine checking into a hotel room where a construction sign flashes outside your window. At first, the blinking light is impossible to ignore. But after a few minutes of watching TV, you barely notice it.

The light still flashes, and your eyes still register it—but your perception of it fades. This demonstrates sensory adaptation: your brain tunes out constant or repetitive information to free up attention for new, important stimuli.