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117 Cards in this Set
- Front
- Back
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What is sound?
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Sound is a form of mechanical energy – essentially molecules pushing up against another. Sound involves pressure waves (changes in pressure), where molecules are either crowded together in high pressure or spread apart in low pressure.
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What are properties of a sound wave?
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1. Amplitude
2. Frequency 3. Timbre 4. Phase |
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Amplitude
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Amplitude is loudness/sound intensity measured in terms of dyne.
It is half the height of wavelength. |
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Dyne
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The unit of force needed to accelerate 1 gram/sec
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What is the quietest sound we can hear?
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0.0002 dynes/cm2
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Decible
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Decibel (Db) express how loud things are in terms of the quietest thing humans can hear. It equals 20 x log(sound in question/quietest sound we can hear).
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What are some examples of Db ratings?
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- 0 = threshold of hearing
- 10 = normal breathing - 20 = leaves rustling in a breeze - 70 = busy traffic (beginning of danger level) - 80 = vacuum cleaner (annoying) - 100 = subway train (prolonged exposure can cause hearing loss) - 140 = jet at takeoff (threshold of pain). |
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Frequency
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Frequency is measured in Hertz (Hz) in cycles/sex - how many waves hit per second. It is related to pitch (how high or low the sound is)
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What are the lowest and highest notes on a piano?
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The lowest note on a piano is 27.5Hz, highest note is 4000Hz
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Timbre
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Pure tones are equal to sine waves. Most sounds we hear in nature are not pure tones. Most of the tones we hear are complex, and a mixture of different frequencies
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Phase
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Phase is the angle of the sine wave.
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How does sound interact with objects?
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• Sound reflects off objects.
• This is the basis of echolocation that bats use. • Sounds can resonate, meaning they can cause the molecules in the object to move. Every substance has a resonance frequency. |
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How does sound interact with other sounds?
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Sounds can reinforce one another. You can take two sounds that are exactly the same pitch and put them together and you end up with one big loud sound. In this case you get twice the compression and twice the rarefaction.
Sounds can also cancel and you will get silence. It's the basis of active noise suppression. |
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What is an example of sound colliding with other sounds?
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Sound can alternate when you play two things that are slightly out of pitch, like 1000Hz and 1004Hz, the sound will alternately reinforce and cancel, it will sound ‘out of tune’
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Why does the ear amplify sound?
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The sound has to be amplified because it’s being transferred from air to fluid inside our ear and uses impedance matching. We lose 30Db of sound when it moves from air to fluid, so we have to make up those lost Db.
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What are the parts of the outer ear?
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1. Pinnae
2. Auditory canal 3. Eardrum |
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Pinnae
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The pinnae are the outer flaps of the ear. Their purpose is to gather sound.
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Everyone has the same shape to their pinnae T or F
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False:
Everyone has a unique form to their pinnae. |
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Why can some people wiggle their ears?
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When you can wiggle your ears that’s a vestige of evolution – how some animals can point their ear in the direction they want to hear sound from.
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What does the way sound is bounced in the pinnae effect?
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It effects your ability to know the location of a sound.
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Auditory canal
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The auditory canal separates the outside world from the inner workings of the ear. The distance of 2.5 cm allows the ear to vibrate in sympathy to certain kinds of frequencies and sounds and amplify the sound pressure.
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What are the two purposes of the auditory canal?
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Protection and sound amplification
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Eardrum
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The eardrum is a very thin membrane that vibrates sound. When you hear a sound the molecules push against each other and ultimately the ear drum which causes it to move. You need to have the eardrum moving to have the signal transfer further on.
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Plugged ear canal
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If the auditory canal is blocked no sound can get in. It can occur in especially small children who put things in their ear or when there's an excessive amount of earwax.
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Swimmer's ear
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When you go swimming water gets in your ear and you don't completely clear it and it stays there. Bacteria start growing in the warm water trapped in the auditory canal. This causes swelling, itching, pain and it is remedied with antibiotics.
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Broken eardrum
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When people get broken eardrums it’s usually because they’ve experienced a really loud sound as well sometimes things get poked in the ear or the person gets hit in the head. You may but a small hole in the eardrum. You don't hear very well and as it heals scar tissue will form, and it will never fully recover to be as good as it was before.
The condition will heal itself in a few weeks. |
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What is the most common way to get a broken eardrum?
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Using Q-tips
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What are parts of the middle ear?
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1. Ossicles
2. Eustachian tubes 3. Muscles of the Middle Ear |
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Ossicles
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The ossicles are three tiny bones - the smallest bones in the body. The eardrum rattles and causes the hammer to move, which hits the anvil and causes the stirrup to move. There is a domino effect. We are transferring the force from the eardrum towards the center of the inner ear.
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What are the three bones?
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1. The Hammer (Malleus)
2. The Anvil (Incus) 3. The Stirrup (Stapes) |
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How do we amplify sound?
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We can amplify sound using two principles. The first is that the ossicles take the force that’s on the entire eardrum and funnel it down into a tiny area. They concentrate the force on a small area at the end of the stirrup. Comparable to a stiletto. The second is that the ossicles amplify force by using leverage. You need a lot more force when moving in water and the ossicles help do that.
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Eustachian Tubes
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The Eustachian tubes connect your middle ear to your throat.
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Why are the eustachian tubes important?
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• It’s an important structure because it equalizes the air pressure on the middle ear and the outer ear. When you swallow the tube opens up and lets air in or out.
• You need to have air pressure the same as in the middle ear as the outer ear. |
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How can we equalize the air pressure?
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Swallow or yawn to open up the Eustachian tubes. If you don't you risk bursting your ear drum.
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Muscles of the Middle Ear
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The muscles contract in the event that you hear a really loud sound. They draw the stirrup away to prevent it from hitting the cochlea so hard and protect it.
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Acoustic reflex
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Protects the ear from low-pitched sounds, and reduces the intensity of the sound by as much as 30 decibels.
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These muscles prevent...
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You from hearing the sound of your own teeth grinding together as you're eating.
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They work best for low frequencies T or F
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True
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Otitis Media
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When there's a respiratory infection, bacteria sneak up the Eustachian tube and get into the middle ear. This produces an earache and bacteria produce fluid, which can burst the ear rums.
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Who are most at risk?
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Children because they have shorter Eustachian tubes
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Cholesteatoma
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You can have scar tissue begin to build up and interfere with your hearing. You may have to have surgery to get it removed.
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Otosclerosis
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This is a hereditary disorder causing abnormal bone growth in the middle ear as the stirrup gets fused which causes deafness. You can remove the stirrup and replace it with an artificial one.
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Conduction problems
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Conduction problems refer to people who can’t hear due to problems with their outer or inner ear. The problem is the sound isn't being conducted from one part to the next.
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What is the problem with hearing aids?
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The problem is they amplify ALL sound, which can get quite annoying. We have the ability to pick out meaningful sound, which doesn’t really happen with hearing aids.
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What are the parts of the inner ear?
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1. Semi-circular canals
2. Cochlea |
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How are the semi-circular canals and cochlea similar?
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Both of the semi-circular canals and cochlea work in similar ways – full of fluid, fluid swishes around and hair cells that wave back and forth. However, the two structures use this information in different ways.
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Semi-circular canals
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Semi-circular canals are involved in the sense of balance. In particular there are 3 of them picking up different kinds of motion.
One is involved in pitch (basically pitching over falling on your face), another one is sensitive to roll and the other is yaw. The inner ear uses the swishing of the fluids as cues to what kind of movement you’re doing. |
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Cochlea
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• The cochlea is a fluid filled chamber about the size of a bean.
• The stirrup pushes up against it transferring sound into the inner ear. • The cochlea is a tube with three parts wrapped up so it’s shaped like a seashell and doesn’t use much space. |
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Close-up on the Cochlea
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• The stirrup pushes up against the vestibular canal and causes movement in the fluid.
• Ultimately the fluid movement is transferred down other levels and when the stirrup pushes in at the oval window, there’s something in the bottom chamber (tympanic canal) that moves outwards that’s the round window. • There’s pressure put on the stirrup, which pushes in and causes the fluid to move. • Pressure is transferred downwards and the round window bulges out. • In the center of the cochlea there’s the cochlear duct (scala media) and it’s got all the fancy workings for hearing. • There’s two forms of fluid in the ear: perilymph and endolymph. |
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Perilymph
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Fluid in the vestibular and tympanic canals. Peri means on the outside, thus it’s on the outside channels. This fluid is watery.
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Endolymph
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Found in the middle canal, the cochlea duct. This fluid is bit on the slimy side with a lot of potassium ions (K+).
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Reissner's membrane
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A very thin membrane a couple of cells thick. Its thickness is useful because it has to transfer pressure from tympanic canals to the cochlear duct.
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Basiliar membrane
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When the fluid in the cochlear duct begins to move it causes the basiliar membrane to move up and down as well.
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Tectorial membrane
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The tectorial membrane is a big flap hanging out in the middle of the cochlear duct. When the fluid in the cochlear duct moves the flap flaps up and down as well. The flap is partly anchored in, so there are some hair cells.
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Inner Hair Cells
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• There are 3,000 inner hair cells per ear.
• They do pitch perception. • There are 40-60 cilia, which are essentially tiny hairs on the hairs. |
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Outer Hair Cells
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• Outer hair cells hook right into the tectorial membrane, anchoring it down.
• There are 12,000 per ear – arranged in three-five rows of w’s and v’s. • They also have cilia on them. • They control the way the basiliar membrane moves. While they don’t do pitch perception per say but they help the inner hair cells do they’re job. |
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Spiral ganglia
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The auditory system works like a screen door. When the screen door is open, potassium ions to come in which increases membrane potential. When the membrane potential becomes positive it results in the release of neurotransmitters to the spiral ganglia.
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Type 1 Spiral Ganglia
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• Large in diameter
• Myelinated. • It sends information farthest away in the brain and takes information from the inner hair cells. |
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What are type 1 spiral ganglia involved with?
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The majority of ganglion are involved in pitch perception
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Type 2 Spiral Ganglia
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• Type 2 is connected to outer hair cells.
• It’s smaller and unmyelinated. • They don’t have to send the information very far. • Involved in a feedback loop that controls what’s going on at the basilar membrane. • Send it to part of the brain that is quite nearby, and that part of the brain communicates back telling the hair cells what to do. |
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What are type 2 spiral ganglia involved with?
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The outer hairs cells are “helpers.” They don’t do pitch perception directly but they make it work better (i.e. by amplifying the wave).
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Frequency Theory (Rutherford)
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Frequency of action potentials correlates to the frequency of the sound (e.g. 100 Hz = 100 action potentials / second)
• If the note is higher, MORE action potentials / second (and vice versa) |
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What is the weak point for frequency theory?
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• The problem is we can hear sounds of up to 20 000 Hz, but there is no way a neuron can produce that many action potentials / second
• Therefore, the weak point of this theory is in explaining how we hear high notes. |
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What is a way around this problem?
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The volley principle
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Volley principle
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one way to help the neurons to keep up, they take turns firing. I.e. neuron 1 reacts to the first crest/ peak of the sound wave, neuron 2 reacts to the 2nd one, and neuron 3 reacts to the 3rd. The volley principle will not work, unless you have another principle: phase lock.
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Phase lock
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Every cell makes an agreement to fire at the same phase angle.
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With these modifications, the theory can explain up until about _____ Hz
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5000
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This theory is best at dealing with ____ frequency sounds
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Low
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Place Theory
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• When you hear a sound it creates waves in the fluid and causes the basilar membrane to move in a certain way.
• Toward the stapes end (the base) the basilar membrane is stiffer, and at the outer end it’s floppier. • As the wave progresses down the membrane - the highest point of the wave is near the base when the sound is low frequency, when the frequency is high, the highest point/ peak of the wave occurs father form the base. • At the peak of the wave the hair cells are maximally active. • In the cochlea, the cells that are responsible for high pitches are close to the stapes, the ones responsible for low are farther from the stapes. |
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What is a weak point for place theory?
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• Low frequency waves, on the other hand, have no clear peak - peak is spread over larger area and isolating the exact peak is much more difficult
• Low sounds are the weak point because the peak is difficult to find/define |
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Place theory deals very well with ____ frequencies
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High
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Neither approach can handle _____ sounds
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LOUD
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What does volume increase?
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The number of action potentials
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What does it mean to say a cell is "saturated"?
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If loudness is too large, cell can’t go any faster than 500 ap/sec (they have a maximum!), so there is a large area that is producing the same number of ap/sec and this creates ambiguity
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Atocaoustic Emissions
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• Strange design feature about our ears
• Sounds that your ears make • Your ears can make sounds up to 20 dB (about the intensity of rustling leaves) • The whole system can work backwards à if the fluid pushes back against the stapes, everything can go backwards and a sound is creates |
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Sensori-neural deafness
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ccurs because you’ve damaged the hair cells in the cochlea
• Can happen by listening to really loud sounds (esp. for an extended period of time) |
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What is the warning sign for sensori-neutral deafness?
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Tinnitus
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Tinnitus
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Ringing in the ears signalling there has been damage to the hair cells.
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The kind of sound most likely to create tinnitus are ___ sounds because it can damage ____ of sounds
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LOW
A LOT |
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Tend to see the effect of damage first in ____ frequencies
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High
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Presbycusis
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"Old" hearing
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Babies hear up to ___ Hz
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27 000
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Teens hear only about ____ Hz
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20 000
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By age 30, you can only hear about ____ Hz
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15 000
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By age 50, it's down to ____ Hz
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12 000
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By age 70, it's down to ____ Hz
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6 000
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How do you make people hear better?
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Lower the frequency
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Why does age cause hearing loss?
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The older you are, the more chance you have had to hear LOUD sounds
• Also, your circulation tends to decrease causing hair cells to die • Good diet and exercise will keep circulation up, and will keep your hearing better for longer |
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Meniere's disease
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Periodic deafness caused by too much fluid in the semi-circular canals. It affects the entire ear and can cause deafness for certain frequencies.
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How is Meniere's disease treated?
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Medications can be taken; special hearing aids can be programmed to amplify appropriate sounds.
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Effects of smoking
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Smoking can constrict and reduct blood flow (arteries) causing hair cells to die. Blood pressure is changeable and also causes hair cells to die. It can cause high frequency hearing loss and essentially ages your hears.
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Effects of viral infections
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Viral infections can kill hair cells, and the particular frequency it affects is random. The high pitched ringing sound is a sign your cells are being attacked.
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Effects of aspirin
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It makes it difficult for your ears to recover from loud sounds and deactivates the outer hair cells. It also influences the ability of the IHCs to work since they work as a team.
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Neural hearing loss
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Affects the spiral ganglion that exit the ear from the auditor nerve.
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Why does neural hearing loss occur?
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Usually because of a tumor on the nerve.
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Cochlear Nucleus
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• First stop from the ear
• Some of the information goes to the inferior colliculus • Some of it goes to the superior olivary nucleus |
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Superior olive
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• Some of the information to the inferior colliculus
• Some of it goes BACK to the cochlea • Superior olive is telling basilar membrane how to move • Feedback loop • Helps motile response • Helps control how the hair cells move |
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Inferior colliculus
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• Right under the superior colliculus
• This is why there is so much cross-modality, since structures are close together • Helps to determine the location/source of the sound • Sound localization - just like superior colliculus makes eyes move to the source of motion/light, etc. |
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Medial Geniculate Nucleus
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• LGN of the thalamus was for VISION (on the side)
• MGN is in the centre • All about sorting information and sending it from one place to the next • Affected by level of arousal • Blocks out a lot of things when you’re falling asleep • Emulating function of MGN when they lower sounds in a movie as someone is falling asleep |
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Auditory Cortex
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• A1 and A2 is just auditory cortex 1 and 2.
• A1 responds very well to pure tones and has a tonotopic map. • It has cells that are responsive to specific tones/ frequencies. • As you work outwards and in particular towards the Belt area (A2) you’ll find cells that are looking for complex and meaningful tones. • The “where” pathway travels up towards the parietal area, the “what” pathway travels in a ventral direction towards the frontal lobe. |
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We are more sensitive to some frequencies than other T or F
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True - Auditory canals resonate to certain frequencies (human speech frequencies, specifically) making them louder.
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When is frequency sensitivity highest?
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3500 Hz
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Auditory masking
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• A sound played in the presence of another sound may not sound as loud as it should
• The general principle is when one sound covers up another sound, the second sound has to be much louder to be heard • The more similar two sounds are (in terms of frequency), the more they will mask each other • Masking is always asymmetrical in that a low sound will mask a high sound BETTER than a high sound will mask a low sound |
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Men's voices are masked more easily than women's. T or F
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False - the opposite is true.
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Why are high sounds masked better than low sounds?
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The reason high sounds are masked better than low sounds is because the mask will cover up a higher proportion of the high sound wave.
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What are the effects of fatigue and adaptation?
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If you had an extremely loud sound at 3000 Hz, you are much less sensitive to the frequency for quite a while later (your sensitivity will increase and return to normal over time)
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What is the closest natural sound to a sine wave?
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The flute
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Combination of many frequencies can still be heard as ONE note. T or F
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True
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In a complex tone, the fundamental town is the ____ frequency
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Lowest
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Periodicity pitch
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Artificial removal of the fundamental, but you still hear it like it's there.
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Timbre
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Timbre reflects the specific mixtures of frequencies (and their relative intensities) you have in a tone.
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How do we know the location of a sound?
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1. Inter-aural time differences
2. Inter-aural intensity differences |
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Inter-aural time differences
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• If something is coming from the right, it will hit the right ear before it hits the left and vice versa.
• Brain compares when the sound hits the left side and the right side first. Ears are very attuned to noticing slight differences in timing (as tiny as 1/60th of 1 millisecond) • If it hits them at the same time it means its either ahead or behind. |
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Inter-aural time differences work better for ____ pitches.
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Low
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Inter-aural intensity differences
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• Differences in loudness.
• If a sound is coming from the left side its louder on the left side than the right. • If something is coming from straight ahead or straight behind it will be equal in loudness. |
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Inter-aural intensity differences work better for ___ frequencies
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High
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How can we tell how far away a noise is?
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When something is farther away we get less sound. People can tell how far away a sound is also based on it's richness.
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