Hearing

The Stimulus Input:Sound Waves

The stimulus energy that comes from sound is in the form of sound waves.

A sound wave’s wavelength is the distance between peaks. Frequency is the number of wavelengths completed in a given period of time. A wave’s amplitude is the height from the bottom to the top of the peaks.

● Short wavelengths mean high frequency(high-pitched sounds)

● Long wavelengths mean low frequency(low-pitched sounds)

● Great amplitude(loud sounds)

● Small amplitude(soft sounds)

small amplitudelarge amplitude

low-pitched sound

high-pitched sound

Decibels are the measuring unit for sound energy. The absolute threshold for hearing is set at zero.

*every 10 decibels equals a tenfold increase in sound

The Ear

In order to hear, sound waves are funneled through the outer ear, into the middle ear, cochlea, and inner ear and then converted into neural activity.

The Mechanism of HearingOuter Ear

● Sound waves are channeled through the auditory canal to the eardrum. The eardrum vibrates with the waves.

Middle Ear● The vibrations from the eardrum are transferred to a piston made up of three bones: the

hammer, anvil, and stirrup.

Inner Ear● The vibrations from the piston are transferred to the cochlea. ● The cochlea’s membrane (also called the round or oval window) vibrates, causing the liquid

inside the cochlea to move.● Movement of the liquid inside the cochlea bend the hair cells located inside the basilar

membrane. This triggers the auditory nerve.● The auditory nerve then sends the message of sound to the thalamus where the signal is

passed on to the auditory cortex where the sound is translated into something that can be understood.

How Do We Perceive Pitch?Place theory (Hermann von Helmholtz) states that we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane.● explains how we hear high pitched sound● does NOT explain how we hear low pitched sounds

Frequency theory says that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, enabling us to sense pitch.● explains how we can hear low pitched sounds● does NOT explain how we can sense sounds with frequencies above 1000

waves per secondVolley principle says that neural cells can alternate firing so that they can achieve a combined frequency above 1000 times per second

How Do We Locate Sounds?With one ear on each side of our head, humans are able to have stereophonic or three-dimensional hearing. Since we hear different sound messages with each ear, it becomes easier to determine where a sound is coming from.

The right ear picks up more intense sound and receives the sound slightly sooner than the left ear.For example, you would hear a car that honks on your right first and it would sound more intense than if one honked on your left side.

Hearing Loss and Deaf Culture

There are two different types of hearing loss:● Conduction Hearing Loss- hearing loss caused by damage to the

mechanical system that conducts sound to the cochlea● Sensorineural Hearing Loss (nerve deafness)- hearing loss caused by

damage to the cochlea’s receptor cells or to the auditory nerves

Once they are damaged, the tissues within the ear cannot be repaired although hearing may be enhanced by hearing aids.

Cochlear ImplantsCurrently, the only way for people with nerve deafness to regain their hearing is with a cochlear implant.A cochlear implant is a device that converts sound into electrical signals