CAN YOU HEAR ME NOW? Hearing. What to Expect/Objectives Describe what hearing is Describe the pressure waves that experiences as sound Describe.

CAN YOU HEAR ME NOW?

Hearing

What to Expect/Objectives

Describe what hearing is Describe the pressure waves that experiences

as sound Describe the 3 regions of the ear Outline the series of events that trigger the

electrical impulses sent to the brain Contrast place and frequency theories Explain how place and frequency theories help

us understand pitch perception Describe how we pinpoint sounds Contrast the 2 types of hearing loss and their

causes Describe how cochlear implants function Explain why deaf culture advocates object to

cochlear implants

Summary

What is hearing? We transduce air pressure waves into

neural messages that the brain interprets as sound

Hearing is highly adaptive – just like our other senses

Like sight, it relies on past experience for perception

Sound Waves

If you slam a book on the desk, the result is that stimulus energy becomes sound waves Molecules of air that bump into each other

Waves expand and compress Like waves in a pond when you toss a stone in

Ears detect the changes in air pressure Ears transform the vibrating air into nerve

impulses Brain then decodes those nerve impulses

as sound

Variations in Waves Strength = amplitude = loudness Frequency = pitch

Long waves have low frequency and therefore have low pitch

Decibels are the measuring unit for sound energy

Absolute threshold for hearing is zero decibels

Every 10 decibels is a 10- fold increase in sound

Normal conversation is 60 db, whisper is 20 db

Prolonged periods over 85 db can create hearing loss

The Ear

The ear converts sound waves into neural activity through a mechanical chain reaction

1. Outer ear channels the sound waves through the auditory canal to the eardrum Eardrum is a tight membrane that vibrates with the

waves 2. Middle ear then transmits the eardrum’s

vibrations through a piston made of 3 parts to the cochlea Hammer, anvil and stirrup = parts of piston Cochlea is a snail-shaped tube in the inner ear

3. Cochlea’s membrane vibrates moving fluid that is in the tube

4. Ripples in the basilar membrane which is lined hair cells

The Ear Continued

5. Hairs bend 6. Bending of hairs trigger impulses in

nearby nerve fibers 7. Nerve fibers converge to create the

auditory nerve 8. Message send through thalamus to

temporal lobe’s auditory cortex

Hairs!

Very sensitive Damage to them can result in hearing loss Cochlea has 16,000 of them Move them by as much as the width of an

atom and it will trigger a neural response Can be damaged easily Loudness is measured by the number of hair

cells that respond If a hair cell loses sensitivity to soft sounds, it

can still detect loud sounds Why someone with hearing loss can hear loud

sounds just the same as someone without hearing loss

Pitch!

Chirp or roar? There are 2 theories on how we hear pitch Place Theory

Helmholtz Different sound waves trigger different activity

in different places along the basilar membrane Brain recognizes pitch by knowing where on

the membrane the neural signal came from High frequencies=large vibrations=beginning

of membrane Low frequencies=vibrations=end of membrane

Pitch 2

Frequency Theory Brain can read pitch from the frequency of

neural impulses Example – if a sound have a frequency of

100 waves per second then those 100 waves per second travel up the auditory nerve, thus there are more neural impulses triggered and our brains know it is higher pitched.

Houston…We Have a Problem

Both theories have “holes” in them Place theory: Can’t explain low-pitched sounds

because the neural signals that are generated cannot be localized so neatly on the basilar membrane

Frequency Theory: Neurons cannot fire faster than 1000 times per second, so how can we hear sounds that we know are above 1000 waves per second (upper third of the piano keyboard).

So…. Place theory best explains how we hear high pitch Frequency theory best explains how we hear low

pitch Combination handles everything in between

Where Did That Sound Come From? The placement of our ears allows for

stereophonic (3D) hearing That is why our ears are where they are

and why we have 2 of them We are great at hearing things on either

side of us, but not directly above us, below us, ahead or behind.

There is parallel processing in hearing too

Hearing Loss

Ear is intricate and delicate, therefore it is “injury prone”

Conduction hearing loss – problem with mechanical system that gets waves to cochlea

Sensorineural hearing loss – damage to hair cell receptors or associated nerves

Once tissue is dead it remains dead Generally caused by heredity, aging and

exposure to loud noises Hearing aids can amplify sound Have found a way to generate new hair cells

in other animals – hope for humans.

Cochlear Implants

Bionic ear! Electronic device that translates sounds into

electrical signals Wired to the cochlear nerves Conveys the info to the brain This is a hotly debated treatment Object to using the devices on children that

became deaf before they learned to speak They argue that it is not a disability and

therefore people should not be labeled as disabled

Sensory Compensation

When you lose one sense, the others tend to compensate and become stronger/more efficient and effective

If an area of your brain is supposed to be used for hearing is not used for hearing then your brain will use it for something else

So…by giving hearing back it will lessen sensory compensation