Intro to Sensation and Perception

What is the difference between sensation and perception, and how do they work? You’ll get to see how the mind handles and differentiates between multiple sensations in this introduction.

Imagine your phone rings. You take it out and see that it’s an unfamiliar number. You’re wary of telemarketers, but you’re also procrastinating doing homework, so you pick up the call anyway. You hear a voice say, ‘hello’; you perceive that the voice is your friend Robert’s. He explains that he’s calling from a friend’s phone because his is dead, and you make plans to see a movie. Even though you didn’t recognize Robert’s number, you heard his voice and recognized it as his. Hearing his voice was sensation; recognizing it was perception. Sensation is passively receiving information through sensory inputs, and perception is interpreting this information.

If you’ve ever been to kindergarten, you’ve probably heard of the five senses: seeing, hearing, smelling, touching and tasting. You probably didn’t learn about proprioception, which is just a fancy way of saying your ability to be aware of your body’s motions and position. All of these senses give us information (sensation) which our brains have to interpret (perception). The senses get their messages to the brain through a process called transduction, or transforming information from the eyes or ears, for example, into electrical impulses that the brain can understand.

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Though each sense works a little differently to do this, psychologists have developed principles to describe overarching ways in which the body deals with sensation and perception. Gustav Fechner, a psychologist in the nineteenth century, called the study of how external stimuli affect us psychophysics. He was interested in the point at which we become aware that we’re sensing something. There could be low music playing in the background at work, and you’d never notice it if you weren’t paying attention to it; if you were bored and the room were silent, you might hear the same volume of music playing as soon as it started.

Psychologist Gustav Fechner studied psychophysics

Psychologists talk mainly about two different kinds of threshold for sensation and perception: the absolute threshold and the difference threshold. The absolute threshold, also known as the detection threshold, refers to the weakest possible stimulus that a person can still perceive. Since perception at these low levels can be a little unreliable, it’s defined as the lowest intensity at which people perceive the stimulus 50% of the time. Those hearing tests you’d take in school are based on the idea of absolute threshold; they’re testing that your hearing is in the normal range by playing softer and softer beeps until you stop being able to hear them. These kinds of tests are known as signal detection analysis, and test your ability to distinguish real sounds from background noise. Your accuracy–your ability to hear real signals and correctly say when there aren’t signals–is known as your sensitivity.

Stimuli that are below your absolute threshold can still affect you. If you’ve heard of subliminal advertising, that’s what’s going on; images that flash by too quickly for us to notice can still influence what we think and feel. For a while, people thought that these subliminal messages could have a real dramatic effect on behavior; their use in marketing was extremely controversial. Traditional advertising tries to persuade you, but ultimately lets you work through the pros and cons and make an ultimate decision yourself. Theoretically, briefly flashing ‘DRINK COKE’ images could bypass our decision-making and give us an overwhelming desire to drink Coke. But most psychologists now believe that while subliminal messages do produce some effect on thinking, it’s fleeting at best and should not be much of a concern for advertising.

Ernst Weber
webers law

The second kind of threshold, the difference threshold, refers to our ability to detect a change in a stimulus’ intensity. This could be the loudness of a noise or the brightness of a light. The just noticeable difference refers to the smallest amount two stimuli can differ so that a person can still tell them apart 50% of the time. Ernst Weber developed a principle, called Weber’s Law, which states that the ‘just noticeable difference’ of a stimulus is proportional to the original intensity of the stimulus. This means that the same increase in strength of a stimulus may be noticeable if the original strength is low, but less noticeable if it’s high. If you’re trying to read by candlelight, and you add another candle to the table, you’re likely to notice a big difference in brightness. But if you’re reading using a light bulb and you add a candle’s light, you won’t notice the difference as much because the reading lamp is a much brighter base stimulus than a single candle. Though Weber’s Law does not hold true for every kind of stimulus (and therefore shouldn’t really be called a law) it’s accurate in a lot of situations, and also represents an important attempt to try to quantify something as seemingly subjective as a noticeable difference.

There are a few more concepts related to attention that affect our abilities to sense and perceive. Just because the sound of rainfall is above our absolute threshold for perception, we’re typically able to ignore it after a while. This is because of sensory adaptation; when we’re exposed for a long time to any given stimulus, we stop perceiving it. Our brains can then pay attention to stimuli that are changing, which are theoretically more important than those staying the same. We also apply selective attention when perceiving the world around us, choosing to focus on certain sensations over others. If you’re concentrating deeply on work, you might not even hear your coworkers’ conversation; but if it’s near the end of the day, you hear everything and want to jump in too.

To sum things up, general questions about sensation and perception are addressed by psychophysics, developed by psychologists Fechner and Weber. Fechner focused on the absolute threshold for perception, while Weber developed Weber’s Law to explain the difference threshold, or the just noticeable difference between one stimulus and another. Additionally, sensory adaptation and selective attention can affect which stimuli we notice, even if all are above our perception thresholds.


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