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

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 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.

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. 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 going to a city that you have never visited. You check into the hotel, but when you get to your room, there is a road construction sign with a bright flashing light outside your window. Unfortunately, there are no other rooms available, so you are stuck with a flashing light. You decide to watch television to unwind. The flashing light was extremely annoying when you first entered your room. It was as if someone was continually turning a bright yellow spotlight on and off in your room, but after watching television for a short while, you no longer notice the light flashing. The light is still flashing and filling your room with yellow light every few seconds, and the photoreceptors in your eyes still sense the light, but you no longer perceive the rapid changes in lighting conditions. That you no longer perceive the flashing light demonstrates sensory adaptation and shows that while closely associated, sensation and perception are different.