8.1: Sensation vs Perception

Learning Objectives

• Distinguish between sensation and perception
• Distinguish between top-down and bottom-up contributions to perception
• Describe key principles, such as transduction and sensory adaptation

Brief Overview:

The topics of sensation and perception are among the oldest and most important in all of psychology. People are equipped with senses such as sight, hearing and taste that help us to take in the world around us. Amazingly, our senses have the ability to convert real-world information into electrical information that can be processed by the brain. The way we interpret this information-- our perceptions-- is what leads to our experiences of the world. In this module, you will learn about the biological processes of sensation and perceptions as well as key differences between these two processes.

Sensation and perception are often intertwined, however, there are important distinctions between the two. The physical process during which our sensory organs—those involved with vision and hearing, for example—respond to external stimuli is called sensation. Sensation happens when you taste noodles or feel the wind on your face or hear a car horn honking in the distance. During sensation, our sense organs are engaging in transduction, the conversion of one form of energy into another. Physical energy such as light or sound is converted into a form of energy the brain can understand: electrical stimulation (i.e. action potentials). After our brain receives the electrical signals, we make sense of all this stimulation and begin to appreciate the complex world around us. This psychological process—making sense of the stimuli—is called perception. It is during this process that you are able to identify a gas leak in your home or a song that reminds you of a specific afternoon spent with friends.

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 involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input, your eyes are not the only way to use bottom-up processing. Imagine you are in the forest walking and you are admiring the trees and nature around. As you continue to walk you hear crackling noises and you begin to smell burning wood. As you continue walking you hear people talking and the crackling and smell of burning wood becomes stronger, at some point you may realize you are entering campgrounds, you can't see the campgrounds but bottom-up processing with the help of your other senses tells you what is going on.

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. One way to illustrate these two concepts is with our ability to read. Read the following quote pictured in Figure 8.1.1 out loud:

Figure 8.1.1 An example of stimuli processing.

Did you notice anything odd while you were reading the text in the triangle? Did you notice the second “the”? If not, it’s likely because you were reading this from a top-down approach. Having a second “the” doesn’t make sense. We know this. Our brain knows this and doesn’t expect there to be a second one, so we have a tendency to skip right over it. In other words, your past experience has changed the way you perceive the writing in the triangle! A beginning reader—one who is using a bottom-up approach by carefully attending to each piece—would be less likely to make this error. The above demonstration illustrates how our experiences can influence the way our brain processes sensory information.

Another way to distinguish between perception and sensation 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, which 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.

When we experience a sensory stimulus that doesn’t change, we stop paying attention to it. This is why we don’t feel the weight of our clothing, hear the hum of a projector in a lecture hall, or see all the tiny scratches on the lenses of our glasses. Thus, when a stimulus is constant and unchanging, we experience sensory adaptation. This occurs because if a stimulus does not change, our brain quits responding to it. A great example of this occurs when we leave the radio on in our car after we park it at home for the night. When we listen to the radio on our way home, the volume seems reasonable. However, the next morning when we start the car, we might be startled by how loud the radio is. We don’t remember it being that loud last night. What happened? We adapted to the constant stimulus (the radio volume) over the course of the previous day and increased the volume at various times.

Attribution

• Sensation and Perception sections adapted by Isaias Hernandez from "NOBA-Vision"; https://nobaproject.com/modules/sensation-and-perception
• Vision sections adapted by Isaias Hernandez from "Sensation vs Perception"; https://www.oercommons.org/courses/i...erception/view