The auditory system (lec. 6)

Question 1

Sound wave

Answer 1

Oscillating movement in the air caused by vibrations of objects
in the environment

Question 2

Outer ear

Answer 2

Collects and focuses sound waves
* Pinna
* Ear canal

Question 3

Middle ear

Answer 3

Transfers and amplifies sound vibrations from outside (air) to inside (fluid). The eardrum separates the outer and middle ears. Vibrations from the canal make the eardrum vibrate, which in turn agitates the ossicles (malleus, incus, stapes), which exist in a special kind of fluid.

Question 4

Hearing aids

Answer 4

Tools that help amplify sounds. They are meant to be put in the outer ear. There is a microphone facing outwards, an amplifier in the object itself, and a speaker facing inwards (towards the middle ear)

Question 5

Good vs. bad hearing in animals

Answer 5

• Animals with good hearing: dogs, bats, elephants, rabbits
• Animals with bad hearing: naked mole rats, salamanders, armadillos, octopi
  We can notice that the animals who hear well have visibly larger ears (large pinna)

Question 6

Inner ear

Answer 6

Converts sound vibrations
into neural signal (through transduction)
* Cochlea (with a tonotopic map: location based on frequency of sound)
* Basilar membrane (at the bottom of the cochlea, follows the spiral, contains hair cells that help transmit sensory info from the membrane into an electrical signal for the auditory nerve)
* Auditory nerve (goes from the ear to the thalamus and then the auditory cortex)

Question 7

Cochlear implants

Answer 7

Tools that deliver sound directly to the auditory nerve (in case of transduction deficiency from the basilar membrane). It is put in by a surgical process. Its goal is to bypass the whole outer, middle, and inner ears. There is a transmitter on the outside of the head and a receiver + stimulator on the inside. Electrodes are placed all along the basilar membrane into the cochlea so that it can directly stimulate the auditory nerve.

Question 8

Primary auditory cortex

Answer 8

Found deep into the temporal lobe. It also has a tonotopic representation. The sensory information from different parts of the basilar membrane goes directly to the part of the auditory cortex that responds to the frequency of that sound.

Question 9

Secondary (association) auditory cortex

Answer 9

More external/lateral in the temporal lobe than the primary auditory cortex. It has higher level functions, like processing what kind os sound/music/speech you’re listening to or what object is making the sound.

Question 10

Perceiving location

Answer 10

• Interaural time difference (sound arrives first at ipsilateral ear)
• Interaural level difference (head shadow reduces sound level at contralateral ear - so you hear the sound louder in the ear that is on the same side as the sound)

Question 11

Complex sound waves

Answer 11

You never hear singular sound waves. A complex sound wave is a combination of simple sound waves. The brain receives imput in form of complex waves and then separates them to analyze them, so that it can recognize the different auditory objects that emitted the different sounds.

Question 12

Fetal hearing

Answer 12

Hearing is one of the first senses that the fetus develops in the womb. Scientists have tested fetus hearing and found that they can actually react to what they are hearing. New research showed that babies in utero can learn a nursery rhyme by hearing their mom’s voice and remember it weeks after the mother has stopped speaking the rhyme. Even when they hear another voice reading the rhyme, their heart rate goes down (just as it did when their mother read it to them). Also, newborns recognize their mother’s voice, and even language, right away, because they have experience from their time in the womb.

Question 12

How does the brain know how to decipher complex sound waves?

Answer 12

The brain doesn’t know whether the sound wave is constructed from different sounds of different auditory object or if it only comes from one source that emits a complex sound. The brain uses different strategies (ex. previous knowledge of what a certain object sounds like, location of the auditory object, etc.) to break down an auditory scene into its different components.

Question 13

Misophonia

Answer 13

Disorder of decreased tolerance to specific sounds (ex. chewing, slurping, heartbeat, silverware…). These “triggers” are experienced as unpleasant or distressing and tend to evoke strong negative emotional, physiological, and behavioral responses that are not seen in most other people. The response can even be generated by thinking about the sound.

Question 13

Prevalence of misophonia in population

Answer 13

Around 10-20% of the population. Some people have more extreme responses to it: around 1/5 of people with misophonia suffer from suicidal thought.

Question 14

Misophonia reaction physiology and explanation (for rough, high-pitched sounds)

Answer 14

Heart rate increases, sweating, tingling, etc., often in reaction to rough, high-frequency sounds. Scientists think it might be due to a survival instinct. Maybe rough sounds like this might be a sign that we need to avoid certain circumstances. Or maybe if there’s a loud growl, we should, not go near that animal. High-pitched scream could also create some negative response in us.

Question 15

Non-evolutionary misophonia

Answer 15

Having the same bodily reaction, but for a sound that has nothing to do with the alarming sounds you could hear in nature (so not rough/high-pitched), ex. people chewing. There are individual differences in how we perceive that kind of sound. For example, the types of sounds that are present in ASMR videos calm some people but induce misophonia in others (they are often used as a prime example of misophonia).

Question 16

Most common sounds inducing misophonia

Answer 16

• Sounds from mouth + nose (chewing, slurping, sniffling…)
• Other human sounds (ex. typing on a keyboard, heels, clicking a pen…)
• Non-human sounds (water dripping, a clock ticking, etc.)
  People with misophonia experience more discomfort for all types of sounds, but in general, across the population, mouth + nose sounds are the ones that cause the most discomfort.

Question 17

Is misophonia a hearing disorder?

Answer 17

Probably not: most people with misophonia don’t react at the same intensity depending on the source of the sound (ex. they don’t like a human’s eating sound but they don’t mind a turtle’s). Studies showed anecdotally that people with misophonia don’t mind as much when it’s a baby or an animal making the sound, or themselves (but don’t like it when it’s another adult/child, ex. family, roommates, significant other, coworker…)

Question 18

Physiological markers of misophonia

Answer 18

People with misophonia sweat more to trigger sounds than control sounds (and so obviously sweat more than control participants to trigger sounds). Heart rate data shows the same thing. Brain imaging showed more activity in the insula in participants suffering from misophonia when hearing a trigger sound.

Question 19

McGurk effect

Answer 19

A perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound.

Question 20

Treating misophonia

Answer 20

Using the McGurk effect, scientists show an image of something that doesn’t typically emit a triggering sound, but use the audio of a triggering sound. The McGurk effect ensures that the patient doesn’t perceive the trigger as a trigger, but rather an independent sound that the neutral object is emitting, reducing the physical reaction.