Sensation and Weber’s Law (Perception Series)

Kat Thomson
Lesson by Kat Thomson
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Sensation and Weber-Fechter Laws. This is the overview of entire psych/soc section. And this is the overview of 6A which is the first. So we're looking at these concepts in this lecture. In terms of sensory processing, there is a difference between sensation and perception.

You likely already know this and if you didn't you probably could guess the difference. But let's go over it anyway. So, a sensation is the stimulation of the actual sensory receptors on the body or in the body. And that results in neural impulse activity.

And it's triggered with or by something in the environment. Whereas perception is what happens at the level of the brain. So that's the filtering, prioritizing, and the subjective interpretations of what has been presented. And there are more than two ways actually that stimuli produce changes in the nervous system.

There are two that I think are important to highlight for the MCAT. One is what's often called Sensory Adaptation and I've also seen it as Habituation. Habituation is a little broader so I mean Habituation can mean all sorts of stuff. But Sensory Adaptation for sure, sometimes called Habituation, is when stimuli are perceived to be less strong once your senses adjust.

The sound of a loud lawn mower outside sounds really loud when it starts and over time it's almost kinda like you feel like you're blocking it out a little bit and part of it probably is that. But there's also this, your neurological and brain process that has to do with neurotransmitter changes and that's kind of a different language or a different set of lessons.

But anyway this happens, right? Also the smell of grass, yeah. I think we can all relate to that phenomenon of going outside and noticing, that, wows. That's really a strong smell of fresh grass, especially if it's maybe spring and you haven't smelled fresh grass in a while.

I mean, I live in California, so it's kinda year round, but I used to live in Idaho and Maine so anyway. One more example. Then there's sensitization which is just the opposite. So this is when a particular stimulus causes a stronger reaction then it once did.

And this is frequently seen in people who've experienced trauma or strong emotional experiences, such as a gunshot going off blocks away and the person is sensitized to that particular sound. And has a very strong, sometimes even what is called a startle response to the sound of the gunshot. There's also something called Cross Sensitization that can occur.

And this is when an acquired sensitivity to a sound, or anything really affecting the body like a drug can result in sensitivities to experiences the brain perceives as similar. And, yeah, so there are tons of examples of this in terms of pharmacology. And it can also just be in terms of sound. So, a sound that doesn't really sound that much like a gunshot but maybe it's kind of loud and concise like a gunshot.

And if you're already sensitized to guns, you might also be sensitized to other types of sound. That's very, very frequent among PTSD folks to the point where some PTSD people have difficulties with all loud noises or with noises that others might not perceive as loud at all. Something called the Absolute Detection Threshold, and that's just the lowest level of intensity at which a stimulus is detectable by an individual.

Below this, there is no sensation. This is a kinda fun chart. You might have seen it before. It's been reproduced many a times, it's an old one. And this is just kind of looking at what would be the absolute threshold for vision, candle flame 30 miles away.

It's kinda hard to believe, but I'm sure they did some sort of test on that, okay. Hearing tick of a watch 20 feet away. Taste 1 teaspoon of sugar in 2 gallons of water. Smell 1 drop of perfume in an apartment. Touch a bee's wing falling on your cheek from 1 centimeter above, okay. So I'm not sure exactly how scientific this is, right?

There are many different variables, we know nothing about this study. But it's kind of poetic and cute. Signal Detection Theory says that, first of all, it's extremely broad. It's used a lot now in psychology really I think almost as like a whole category of thought and study. So it's a theory, but it's really big.

Okay, multiple factors influence whether an individual will detect a stimulus, including the intensity of the stimulus. Any kind of competing stimuli in the environment, and also the unique traits and experiences of that individual. Now before signal detection, signal detection theory, there was Weber's Law.

So this is going back to the mid-1800s. And before giving you a definition, I'll just go through a little example. Question. Will you be able to perceive the difference in weight? You hold out your hand. I put a quarter in it.

I tell you to close your eyes, and then somehow I put something else in your hand without you detecting the movement or the sensation. So already there are some problems with this study, but if there was a way to do that basically you would detect the difference in weight. Or if I put one coin in your hand first and then put two that were smooshed together on your hand again, asked you, heavier, lighter or the same, you'd know it was heavier most likely.

However, if you have a 5 kg dumbbell and I put that same quarter on the dumbbell, you won't be able to detect the difference in weight. The definition, then, of Weber's Law is that there is a ratio relationship between the original intensity of something and the threshold at which humans can perceive a change in intensity. Now, it's often called the Just Noticeable Difference.

And is all dependent on how intense is the beginning object. This is the equation for it, not sure you would need to know it, but there it is and compared to a lot of the physics equations, this is like kind of like baby physics, right? So you'll be able just to recognize that I think. Let's say that your initial stimulus was 10 pounds and we're looking at weight.

The constant ratio for weight is, it's actually a little less than this, but let's just say it's 10%. If I put something in your hand or on your head or who knows what that was 12 pounds you would be able to detect that because that is larger than 10%. And there was a 100 pounds, I put something that was a 100 and, well, yeah, it could be, yeah, let's do 105 pounds.

Most likely, you might be able to, right? Cuz that's 5%, so you might be able to. But it's also possible that that would be under the just noticeable difference, so the level of detection. Here's another way of looking at it. And so this would be the background intensity, meaning what are we starting out with.

And then this would be the level if we're looking at 10%. Of an increase at which you would be able to perceive there was a difference. So once you get to 11, you would notice there was a difference. If you're at 100, 110. One thing about Weber's Law is that it was devised to apply to a variety of sense modalities so not just weight but auditory and visual, weight tends to be, it's just easier to measure.

There are just so many factors that go into sound and vision. So weight's a good one to go through with this set of examples. Now, it's called, though, sometimes, Weber-Fechner laws, there were two combined. Weber-Fechner Fechner was actually the one who coined Weber's Law. He was one of his students, that was in 1850.

And so although it was inspired by Weber, it was actually Fechner who wrote it up. And Fechner is also known for this term, ''psychophysics'' which is an MCAT topic, it's on that list I showed you at the beginning. He coined the specialty and it's also just kind of like a field of investigation. And it's an area in psychology, usually its like in neuropysch, or biopsych or cognitive psych, that investigates how stimuli affect sensations and perceptions.

And it was actually kind of side note sort of interesting I think, the psychophysics term was Inspired Freud, I've read in sources, to use his term psychoanalytic. So I don't know, maybe a little bit of a stretch, but I've heard that connection be argued for. And his work, Fechner's, was important in the eventual creation of the decibel by Bell in 1929.

Now Fechner had a bunch, well he had like one other really famous law and many, many, many other theories. But eventually he started to graph all of this in terms of logarithms. But the Weber Law is a very simple ratio and that's the one that's important for you to know. The just noticeable difference has been applied a lot in marketing to study Consumer Behavior.

So let's say you are in the business of, I don't know, I was gonna say frozen pizza but it looks like it's probably a hot pizza. You make pizzas, that's your job. And you and your company are trying to cut costs. So you think about, let's make it just a little bit smaller. Or let's make some of the ingredients just a little bit cheaper.

You want to make sure if you make those changes that you're making changes that are smaller than the just noticeable difference. Right, if you're trying to cheat, well, that wasn't nice, but if you are trying to not lose customers. Okay, however if you are advertising the latest and the greatest addition to your product, you want it to be a big enough change that people will appreciate the change.

You don't want to change a couple of ingredients and have nobody be able to detect the difference. So there are tons of theories on just noticeable difference in consumer behavior and I can absolutely imagine that coming up in an MCAT question. Let's do a question here. Okay which of the following is an example of sensory adaptation?

A, You used to wake up at night whenever a siren went off, but since you moved to the city, you don't notice them. Yeah, maybe. I mean, I don't know, we're talking about multiple days here and weeks. I don't know if that's the same thing as a lawnmower outside, but let's say maybe. B, It used to bother you that the person down the hall clears his throat several times an hour, but you reasoned he might have a health problem.

So it no longer bothers you. No. This is like conscious stuff. This is cognitive. This is all sorts of nice empathy. But, no. C, You ate too many Doritos as a kid, and now you can't stand the taste.

No. That's based on, that's based on memory. It's not about adaptation of the senses, it's more of a learning type situation rather than a sensory situation. So actually it is this, it's A. And that is one example. Of course when you're asleep you're not conscious.

This is something that your whole sensory system adapts to, when you're exposed to louder noises over time. Okay, so, good luck with your study, and I'll talk to you later.

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Psychology I (Foundations)