What is the process through which we receive stimuli from the external environment and organize and interpret them?

By Catherine A. Sanderson, Amherst College

Take a minute and try to summon up the melodic and low-pitched sound of Morgan Freeman’s voice. The power of Morgan Freeman’s voice provides insight into how our sense organs—our ears in this example—gather information about the physical world. This is what psychologists refer to as sensation. But the inferences we make about his voice—say, a sense of strength—reflect a different process, what psychologists describe as perception.

Sensation vs Perception

These two processes, sensation and perception, are different, but closely related. Sensation describes physical input about the environment received by various sensory receptors in our eyes, ears, nose, and so on. Perception is the process by which we make sense of this input; how the brain automatically selects, organizes, and interprets these sensations.

Here’s an easy way to think about the difference. Sensation is largely a physical process, whereas perception is heavily influenced by psychology. This is why the exact same physical stimuli can be perceived by different people in different ways. 

Let’s say you and a friend walk into a bakery and immediately smell freshly baked cinnamon rolls. Both of you may sense the odor of cinnamon. But this smell may be perceived by one of you as simply a pleasant odor and hunger pains, and by the other as a happy feeling prompted by memories of your grandmother’s kitchen. 

Different people perceive the same exact sensation in different ways because each person’s brain interprets things differently, based on their mood, memories, and expectations.

Transduction through Five Senses

Sensation starts with specialized receptor cells located in our sense organs: our eyes, ears, nose, tongue, and skin. First, we detect some stimulus in the environment: we see a robin flying outside our window, we smell cinnamon rolls as we walk by a bakery, we hear Morgan Freeman’s melodic voice as we’re listening to the radio. We then take in that sensory information and convert it in our brains to neural impulses. This process is called transduction.

For each of our five senses, the exact same process occurs: sensory receptors take in some form of energy, say light energy, sound waves, or the chemical energy of odor molecules. These receptors then convert the energy from this stimulus into neural impulses, which are sent on to different parts of the brain, the primary olfaction area or the primary audition area, and so on.

Sensory Reduction

But keep in mind that not all sensory information is sent on for processing in the brain. Instead, the information we received from the environment is first analyzed and filtered in a process called sensory reduction. This filtering prevents our brain from being overwhelmed by all of the sensations we’re constantly exposed to: The feel of our socks rubbing against our feet, or the sound of blood rushing through our veins.

The field of psychophysics examines these links between the physical characteristics of stimuli and our psychological experience of them. Imagine you are in a crowded restaurant. Your attention is on the people you’re dining with and the food you’re eating.

You ignore many other sensations around you—the wait staff bringing people menus, the aroma of assorted dishes, the conversations people are having at nearby tables—unless they happen to be particularly intriguing.

This article comes directly from content in the video series Introduction to Psychology. Watch it now, on Wondrium.

Not Noticing a Baby’s Cries

So, what determines whether we can detect a particular stimulus of light, sound, smell, and so on? One factor is the amount of the stimulus present. The absolute threshold refers to the minimum amount of stimulation necessary to be able to consciously detect a particular stimulus—light, sound, pressure, taste, odor—50% of the time. 

Another type of threshold (a difference threshold) refers to the smallest physical difference between two stimuli that are consciously detectable 50% of the time. This threshold, often called the just noticeable difference, examines whether someone can distinguish between two similar stimuli. 

So, our ability to detect a given stimulus is based in part on the physics of what is loud enough to hear, large enough to see, and so on. But our ability to detect something in the environment is also influenced by psychological factors, including our motivation, expectations, and experiences. 

New parents may be particularly attuned to the slightest sound their baby makes during the course of the night, while more experienced parents may have become habituated not to notice such noise at all. Some people can walk into a room and immediately detect a lingering odor of cigarette smoke, whereas someone else may not notice it at all.

What Air Traffic Controllers and Wine Connoisseurs Have in Common

But there are also some careers where people learn to detect a particular stimulus amidst a sea of background noise. Air traffic controllers have to be able to detect and follow particular planes and ignore the other signals that appear on a radar screen. 

Radiologists have to be able to detect whether an image on a lung is a cancerous tumor or healthy tissue. Wine connoisseurs learn to detect subtle differences between very similar wines that most of us wouldn’t detect at all. These are all examples of trained forms of sensitization.

Similarly, dogs are often trained to provide valuable help in detecting drugs and explosives and assisting in search-and-rescue operations. Some fascinating research suggests that dogs can actually be trained to detect the smell of many types of cancers in humans, even in very low concentrations, before the cancer might be detected through traditional tests.

Common Questions about What Sensation Means in the Context of the Human Body

Q: What is the difference between sensation and perception?

Sensation refers to the process of receiving inputs from the environment through sensory receptors such as ears, and eyes, among other inputs. On the other hand, perception refers to the process of the brain making sense of the sensory information coming through, analyzing, and sorting it out.

Q: What is transduction?

After the first step of sensation, receiving the sensory input from the environment, our brain takes the sensory information and converts it into neural impulses. This process is referred to as transduction.

Q: What happens in the process known as sensory reduction?

The sensory input that we receive in the first step of sensation is not immediately sent to the brain to be analyzed and processed. Instead, the information is first filtered so that the brain isn’t overwhelmed by the sensory information that we’re exposed to on a constant basis. This process is called sensory reduction.

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