SAP - Building Blocks of Sensation and Perception Lesson

 

Building Blocks of Sensation and Perception

Have you ever been through a kids' haunted house? You know, the ones where you put your hand in a bowl of peeled grapes or cold spaghetti noodles and think it's a bowl full of eyeballs or guts? Have you ever watched a scary movie when your parents weren't home, and then suffered for the rest of the evening because every small sound scared you? If so, you've experienced the surprising interactions between sensation and perception.

Each of your senses receives information from the environment, converts it into neural signals in a process called transduction, and sends that information to your brain through your sensory neurons (remember neurons from the biopsychology unit?!). This is the process of sensation. When this sensory information reaches your brain, the thalamus sends the information to the correct part of the cerebral cortex for processing. It is then the brain's job to decide what that sensory information means, to organize and interpret it until it makes sense. This is the process of perception.

In the case of the bowls of grapes or noodles in the haunted house, why did you jump to an incorrect decision? It's because of a process called top-down processing, where you have some prior knowledge or assumptions about what we're supposed to be interpreting. You knew it should be scary, so you filled in the blank places so you could have a complete experience. And after you'd seen the scary movie, your brain was primed and ready to hear scary noises, so you made some assumptions about every noise you heard for the rest of the night. In both cases, and in most experiences as an experienced person, you didn't rely on just your sensory information because your brain already knew something about what to expect.

Top-down processing is the opposite of bottom-up processing, where we have no prior knowledge about a subject, so we use only sensory information to make a judgment.

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So the big question here is...HOW? How does the brain make sense of the information our senses send its way?

First of all, consider all the things our brain chooses not to notice every minute of the day. What if you spent all your time noticing the feeling of your socks encasing your feet, your eyelashes brushing your cheeks as you blink, your chest moving as you inhale and exhale, and the million other sensations that could assault your senses all the time? Thank goodness we have selective attention, which allows us to focus on only a tiny bit of the information we're experiencing every moment! While focusing our attention on one thing, we are effectively blind to other stimuli in our environment, a phenomenon called inattentional blindness. One famous experiment asked people to count the number of times players in a video passed a ball to each other. Half of viewers were so busy counting that they missed a man in a gorilla suit walking through the players! Do you ever wonder how much you miss because you're looking at your phone screen? It's probably a lot!

Selective attention tells us that we simply can't pay attention to all the stimuli around us all the time because our brains would be overloaded. But what about all the information that we can't pay attention to? Dogs can hear whistles that we can't hear. Rattlesnakes can see infrared light that shows them heat. Elephant trunks and feet can sense vibrations up to 10 miles away. Honeybees can sense the earth's magnetic field, ensuring that they're always headed in the right direction.

Animals whose senses differ from ours have different absolute thresholds. The absolute threshold is the point at which we can just barely notice a stimulus. Any more and we'd always be able to sense it; any less and we'd never be able to notice it. The absolute threshold is that magic point where a human is capable of noticing the stimuli 50% of the time. You may remember taking a hearing test at the doctor or with the school nurse. You were supposed to raise your hand when the noise passed the absolute threshold and you could just start to hear it.

Try this perception experiment for yourself - Good Luck!

Complete the basics of sensation activity below:

 

 

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