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HOMUNCULUS! It’s a big and weird word that you may or may not have heard before, but do you know what it means? In this episode of Crash Course Psychology, Hank gives us a deeper understanding of this weird model of human sensation.
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Transcript Provided by YouTube:
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Homunculus!
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If you’ve heard that word, it probably wasn’t in the context of psychology.
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A monster in Dungeons and Dragons, a song by They Might Be Giants, the bad guys in Fullmetal
00:08
Alchemist, a novel by James Blaylock.
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It’s Latin for ‘little man’ and in psychology, it refers to a kind of sensory map of the
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human body, a depiction of what we’d look like if each of our parts grew in proportion
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to how much we sense with them.
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Witness!
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Look at this dude.
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His ham hands could rip off a car door.
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I mean, if he could lift them, which he couldn’t.
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Is this what we’re supposed to look like on the inside?
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This freaky thing illustrates the weighted significance of our sensory receptors.
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His disproportional hands are monstrous, for example, because we primarily touch the world
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with our hands, not our elbows, so our hands are extremely sensitive.
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His mouth, meanwhile, is huge because we also have a ton of sensory receptors in our tongues
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and lips.
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It’s what we use for tasting food and for sucking face.
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As we continue our exploration of how we both sense and perceive the world, the Homunculus,
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while kind of freaky, is actually a pretty attractive model for understanding how our
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bodies interact with the environment.
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How we smell it with our outsized nose, taste it with our ridiculous Mick Jagger lips, and
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touch it with our enormous Donkey Kong hands.
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So join me, as we get to know the hideous little creature within you.
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[Intro]
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Last week we talked about the difference between sensation and perception: how sensation is
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the process by which our senses and brain receive information from the outer world,
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while perception is how we organize and interpret that information and give it meaning.
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Like, right now, my sense of hearing is letting me detect sounds, while my brain is processing
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and interpreting them, allowing me to identify and perceive the individual sounds and determine
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if they’re coming from the radio, or outside or right behind me.
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Sound moves in waves that vibrate through a medium, like air.
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And although they function differently that waves of electromagnetic radiation, including
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what we think of as light, sound waves also can vary in shape.
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Short waves have a high frequency and a high pitch, like a plucky violin.
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Long waves have a low frequency and pitch, like a mournful cello.
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Wave height, or amplitude, determine a sound’s loudness, which we typically measure in decibels.
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And just as light waves become electrical impulses that we register with our sight,
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so too do our ears turn vibrating air into signals that our brains can decipher.
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While the human ear might not be as elegant as the jackrabbit’s, or as wild as the long-eared
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bat’s, it’s actually a pretty incredible organ.
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Or, organs, since we have two of them, which helps give us directional stereophonic hearing.
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That’s the 3D type of hearing we couldn’t experience if we had just one big, freaky
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ear in the middle of our foreheads.
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Your outer ear, the part that you can see and pierce and tug on, collects sound waves
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and funnels through the ear canal and into the middle ear, where they cause your eardrum
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to vibrate.
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From there, sound vibrations are amplified by the so-called ‘ossicle bones’, which also
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happen to be the most awesomely named bones in your body: the stirrup, the hammer and
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the anvil.
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From here, those physical vibrations travel to the inner ear, where they bump into the
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snail-shaped cochlea, and its surrounding fluids get jostled around, causing some of
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your 16,000 tiny cochlear hair cells to bend.
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This motion triggers neighbouring nerve cells that convert that physical energy into electrical
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impulses zipping up the auditory nerve into the auditory cortex, where the brain is like
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‘Oh, songbirds!’, or ‘Elvis!’, or ‘Vengeance!’, or whatever.
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And you know what goes great with a little bit of rockabilly, or revenge?
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A nice meal.
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One of the greatest joys in life is enjoying flavors; whether you prefer casserole or caviar,
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we all get our tasting done in the same way, starting with our taste buds.
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Each of our thousands of taste buds contains a sort of pocket-like pore that contains fifty
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to a hundred hair-like taste receptor cells that read food molecules and report back to
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the brain.
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“That chip is salty, that lemon is sour.”
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Now, everybody used to think that our tongues just detected four distinct tastes: sweet,
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salty, sour and bitter.
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And you’ve probably seen the version of this bogus taste map, which incorrectly assigns
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certain tastes to certain parts of your tongue.
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But we now recognize a fifth flavour: the savoury, meaty, MSG-y taste, for which there
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is no English word, it’s known as ‘umami’.
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But taste is nothing without smell.
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Plug your nose, and a bite of cold bacon is just a mouthful of salt.
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This is a prime example of sensory interaction; the principle that one sense can influence
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another.
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I’ll get back to smell in just a bit, but I want to take a moment to talk about what
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happens when those sensory interactions get messy.
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Let us take a little questionnaire, shall we?
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Do certain words trigger a strong, specific taste in your mouth?
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Like, does the word ‘kitten’ taste like candy canes?
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Has hearing a sound ever made you see a color?
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Like does Prince’s voice singing Purple Rain actually cause the colour purple to flash
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before your eyes?
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Do you ever feel like you’re being touched when you smell something?
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Like does the smell of lilies give you the sensation of touching a cold, metal surface?
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Most of you said no to all of those questions, but at least one of you out there answered
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yes.
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And more likely than not, that person has synesthesia, a rare and fascinating neurological
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condition where two or more senses get wrapped together.
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This kind of sensory mix up is involuntary, and it’s experienced without forethought in
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a durable and consistent way.
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Like, the number seven is always going to taste like coffee, and it’s never going to
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switch to tomato juice.
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And we’re still not sure what causes this phenomenon.
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One idea suggests that the rogue development of new neural connections may override normal
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boundaries that typically separate the senses.
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Another theory suggests that all babies are born with synesthesia and experience mixed
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sense until the brain matures and creates separate sense channels, unless they don’t,
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in which case you grow up to be a synesthete.
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Yet another theory links the condition to wonky neurochemistry, in which the neurotransmitters
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associated with one function turn up way over in a different part of the brain.
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Just another example of how the mind is still extremely mysterious.
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So, back to the comparatively boring topic of smells that only smell… unlike our wave
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detecting senses of sight and hearing, out taste and smell are chemical senses.
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We differentiate the smells of spring lilacs, grilled cheese, and gasoline when airborne
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molecules travel up the nose and reach the five to ten million receptor cells at the
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top of each nasal cavity; and yes, that means when you smell poop, there’s poop particles
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in your nose.
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These receptors send information to the brain’s olfactory bulb, then zips it on to the primary
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smell cortex and parts of the limbic system responsible for emotion and memory.
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Unlike our five different taste receptors or two types of retinal receptors, we don’t
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have specifically differentiated smell receptors, rather, odour receptors come together in different
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combinations.
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So, just like pressing different keys on your keyboard can allow you to form tons of different
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words, so too can these distinct combinations of activated smell receptors communicate some
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ten thousand unique smells.
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But, how we feel about a smell, and our perception of it, is often tangled up in our experiences
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with that scent.
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If our beloved grandma baked gingerbread every time we visited, those memories may make you
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partial to the smell of gingerbread.
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Even if we can’t immediately name the odor, our brains are amazing at storing and recognizing
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old scents by their associations.
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Which is why you may suddenly feel happy when you walk into a bakery, even before you realize
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you’re thinking of your grandma.
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The emotional power of smell partly has to with how our sense circuitry connects to the
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brain’s limbic system, right next to our emotional registry, the amygdala, and our memory keeper,
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the hippocampus.
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That’s why scents can be so intimately tied with our feelings and memories.
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And how a whiff of Nag Champa can immediately transport to back to eating chips in your
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freshman dorm room.
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Smelling, hearing, tasting, seeing: all fantastic, but if there’s one thing that popular music
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taught us, besides a bunch of really terrible relationship advice, it’s that when it comes
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to our senses, we’re all about touching.
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We’ve got songs about magic touches and golden touches, invisible and human touches.
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Songs about touching ourselves, touching me, touching you, and even what you can’t touch.
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Touch is extremely important, especially during early development.
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Baby monkeys that are allowed to see, hear and smell, but not touch their mamas become
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extremely distraught.
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That’s just a mean experiment.
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Premature human babies gain weight faster if they’re held and massaged, and some studies
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indicated that children that didn’t receive enough physical attention as infants are at
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higher risk for emotional, behavioral, and social problems as they grow.
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Your sense of touch is actually a combination of four distinct skin sensations: pressure,
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warmth, cold, and pain.
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If you touch various spots of your skin with something soft like this anglerfish, you’ll
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feel that you sense different amounts of softness on different parts of your body… just put
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that up there…
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The same goes for a warm mug, or an ice cube, or a needle point.
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You’ll sense that some spots are more or less sensitive to each of the four distinct sensations.
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Other skin sensations, like tickles, itches, and the experience of wetness, are just variations
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on those four different sensations.
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Ultimately, your sense of touch joins forces with sensors in your bones, joints, and tendons
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to provide your personal kinesthesis: the way that body senses its own movement and
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positioning.
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You use your kinesthetic sense whenever you walk, dance, swim, or hula hoop.
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It’s what the cops are testing drunk people for when they ask them to touch their noses
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with their eyes closed.
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This sense allows you to detect changes in the position of your body without relying
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on other senses, which is why you can still cha-cha, backstroke, and hula hoop with your
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eyes closed and your ears plugged.
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The partner sense to your kinesthesis is your vestibular sense, which monitors your head’s
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position and your balance.
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This sense of equilibrium is ruled by the pretzel-shaped, semicircular canals and the
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fluid-filled vestibular sacs that connect those canals to the cochlea in your inner
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ear.
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So, if you spin around a bunch and suddenly stop, it’ll take a minute for that inner ear
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fluid to return to normal, which is what makes you feel dizzy.
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That moving fluid is actually fooling your brain into thinking your body is still spinning.
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It’s a good example of how even our normal functioning senses can fool us.
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Understanding exactly how we get fooled helps us understand how our sensual perception system
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works, which is exactly what we’re going to be talking about next time.
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For now, hopefully you realized that your homunculus is actually kinda beautiful, in
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its own way, because you learned how your sense of hearing, taste, smell, and touch
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work.
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And thanks for watching, especially to all our Subbable Subscribers, who make this whole
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channel possible.
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If you’d like to sponsor an episode of Crash Course: Psychology, get a copy of one of our
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Rorschach prints, and even be animated into an upcoming episode, just go to subbable.com/crashcourse.
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This episode was written by Kathleen Yale, edited by Blake de Pastino and myself, and
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our consultant in Dr. Ranjit Bhagwat.
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Our director and editor is Nicholas Jenkins.
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Michael Aranda is our sound designer, and our graphics team is Thought Café.
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This post was previously published on YouTube.
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Photo credit: Screenshot from video.
