- Good morning, afternoon, evening, night, whenever you're watching this. Welcome back to the Mr. Sinn channel. Today we're going to be going over unit 3, topic five. We're going to be talking about auditory sensation and perception. 

So over the past couple of videos, we've spent a lot of time talking about our vision. Now we are going to transition into our hearing. When we are talking about hearing and sound, we can see that sound travels in waves, similar to light. 

The frequency of sound is what will determine the pitch, which is the sound's highness or lowness. If the wave is shorter, the pitch will be higher. And if the wave is longer, the pitch will be lower. Another aspect of sound is amplitude. This is the strength of the sound wave. To measure this, you take the distance from the peak or the trough of the wave and measure from the equilibrium. Think of it like a baseline. One thing to remember is the amplitude is only the distance from the baseline to the lowest point of the sound wave, or the highest point, not the total distance of the wave. The larger the amplitude, the louder the sound. 

Now, sound waves are great and all, but where it gets interesting is when we talk about how we take the different sensory information and process it. Starting with the ear, we can see the ear can be broken down into three parts-- the outer, middle, and inner ear. The outer ear is what receives sound. And it guides it into the ear canal. The outer ear is made up of the pinna, which is the outer part of the ear. This is what you see when you're looking at the side of someone's head. It is made up of cartilage and directs the sound. 

Next is the auditory canal. This is the entrance to your ear. This tube funnels the sound into your ear. This canal sends the sound from the pinna to the eardrum. The eardrum, also called the tympanic membrane, is very sensitive. As the air in the auditory canal vibrates, that causes the eardrum to vibrate and transform the sound vibrations into mechanical vibrations of the bones of the middle ear. 

After the eardrum, we move into the middle ear. This part of the ear is made up of three tiny bones called the auditory ossicles. Moving from the eardrum to the first bone, we have the malleus, also called the hammer due to the bones shape. Then we have the incus, also known as the anvil, and lastly, the stapes, which is also known as the stirrup. 

All of these bones help amplify sound that's sent from the eardrum to the inner ear. One of the reasons why the sound needs to be amplified is because the inner ear contains a liquid. And it's more difficult to move vibrations through water compared to air. Sitting between the middle ear and the start of the inner ear is the oval window. This is an opening in the wall of the cochlea. And it's covered with a membrane that helps with the amplification of sound, sending waves into the inner ear. 

The inner ear is where the sound waves and vibrations get turned into electrical signals, which then go through the auditory nerve for your brain to process. The inner ear is also what helps you balance. It makes sure you know you're up from your down. 

The first structure of the inner ear is one we've already mentioned. And it's the cochlea. This looks like a snail. And like I already said, it's filled with a fluid. It has three canals, one of which is the scala media. The floor of the scala media has two very important structures that sit on it-- the organ of Corti and the basilar membrane. 

The organ of Corti contains the sensory receptors for hearing. The organ of Corti is sitting on the basilar membrane. When the vibrations come into the inner ear, the basilar membrane will vibrate in a wave-like ripple which leads to the movement of the stereocilia. These are tiny hairs that protrude from the hair cells of the organ of Corti along the basilar membrane. When the stereocilia starts to vibrate, this starts the process of converting the vibrations into electrical impulses to send them to the brain. 

So we've been talking about the basilar membrane and also the stereocilia. And I want to quickly talk about the idea that different parts of the basilar membrane and cilia are specific to different frequencies. This is known as the place theory. Certain hair cells respond to certain frequencies. Hair cells at the base of the cochlea can detect higher pitched sounds. Hair cells near the top of the cochlea can detect lower pitch sounds, with the hair cells at the very top, near the spiral, detecting the lowest pitch of sound. 

Now, the second part of the inner ear that we're going to talk about is the semicircular canals. These are located above the cochlea and are filled with fluid. These are essential for balance. When you tilt your head, the fluid shifts, causing the nerves to become stimulated, which sends signals to your brain about your movement and head position. 

Now we're going to shift gears just a little bit and talk about hearing loss. Over time, as we start to age, we can experience hearing loss. Now, that's not the only cause of hearing loss. You can also experience it due to damage done to the ear due to an over exposure to loud sounds or external events. 

Some people experience sensorineural hearing loss, which is when a person's clarity and loudness and the range of sounds are no longer able to be heard. This is because the cilia on the auditory nerve in both ears have been damaged, preventing the brain from getting all of the signals. Oftentimes, this is due to age, disease, or it could be due to external events. 

There's also conductive hearing loss. This happens when sound waves cannot move through the outer ear to the middle ear and lastly to the inner ear. This happens because something is blocking the outer ear or if damage was done to the ear, preventing sound from traveling through the auditory canal. 

One way in which hearing loss can be treated is by a cochlear implant. This is a device that converts sounds into electrical signals. These signals then help stimulate the auditory nerve and allow for the signals to be sent to the brain. Another medical device that is used to treat hearing loss is a hearing aid, which simply amplifies the sound. 

And just like that, another topic review video is complete. Now, you know the drill. Answer the questions on the screen to make sure you remember all this important information. Check your answers in the comments section below. And don't forget to hit that Subscribe button. Also if you need more help with AP Psychology, don't forget to check out my Ultimate Review Packet. You can find it in the description of this video. It's a great resource that will help you get an A in your class and a five on that national exam. As always, I'm Mr. Sinn. And until next time, I'll see you online. 

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