What are the functions of hearing?

Signaling events we cannot see and Facilitation of communication

What is sound and its definition?

travelling pressure wave that is sound. Travels through the air at 340 meters per sec and through water at 1,500 meters per sec

change in compression of air molecules is a sine wave ~ (compression that is moving)

definition of sound: 

Physical definition:  sound is pressure changes in the air or other medium. 

Perceptual definition: sound is the experience we have when we hear

What is amplitude and how is sound measured and what is the advantage of this?

Amplitude is the height of a sine wave

Sound pressure is discussed in terms of decibels (dB) 

dB = 20 x log ^p/_po 

P = sound pressure

 Po = standard pressure (20) 

 If p = 20 (micro pascals) then dB = 0 

Note log1 = 0, log10 = 1, log100 = 2 etc

 If p = 200 200/20=10 log10=1 20*1=20 therefore , dB = 20  SPL

If sound pressure = 2,000 what is dB equal to? 

dB = 20 x log 2,000/20 

dB = 20 x log100 (log 100 = 2) 

dB = 40 SPL (sound pressure level)   

the advantage of using dB

compression of  a scale that covers a huge range, to a more manageable range.

What is Fourier analysis and synthesis and what is involved them?

Fourier Synthesis is adding together frequencies to create a complex tone.  

Fourier analysis – the process of decomposing a complex tone into its component frequencies/harmonics 

Fundamental frequency - lowest frequency present a.k.a the first harmonic.  

Harmonic - frequencies which are multiples of the fundamental frequency 

Fourier spectrum - plot showing sinewave components of a sound

How is sound quality effected?

Through periodicity pitch. This is when the Removal of the first harmonic results in a sound with the same perceived pitch, but with a different timbre.  The brain fills in the missing fundamental frequency

difference in timbre is due to  Different harmonics and Differences in the attack and decay (build up and fall off of a tone).   Modifying the attack and decay makes it difficult to identify which instrument in being played.   

What is the audible hearing range for humans and how is this graphed?

Range is between about 20Hz and 20,000 Hz

audibility curve plots the range of frequencies an observer can hear and what intensity is required to just detect them.

Equal loudness curves show how loud a tone of a particular frequency has to be to match a standard tone of a given frequency and loudness.

Audiograms the same as the audibility curve, but inverted   Used by clinicians to interpret hearing loss eg. Presbycusis

Name and state the function, regions and structures of the ear

Outter, Middle and inner reigons

The outer ear Consists primarily of the Pinna, and auditory canal 

channels sound to the other parts of the ear through the auditory canal which intensify some sounds via resonance. resonant frequency determined by the length of the canal.  is between 2,000 and 5,000 Hz (frequency of human voice)

middle ear comprised of the ossicles (malleus, Incus & Stapes)

Role is to enhance the sound pressure before passing it on to the inner ear.  Through concentrating force and leverage 

Leverage Principle: by using leverage it is possible for a very small force to move a big object. 

Inner ear consists of the cochlea

Sound pressure is transduced into electrical energy inside the organ of the corti

Hair cells in the organ of corti are the receptor cells for sound pressure and transduction Bending of hair cells open ion channels which creates the transduction into electrical energy

Close and open based on direction of bending. Very little movement necessary

Cochlear implants is a practical application of what? How was this found and what evidence is there for it?

Place coding founded by Von Bekesy and is the  primary means of coding frequency is

Found that different frequencies stimulate different locations along the basilar membrane because . The base is narrower and stiffer than the apex and therefor resonates better with higher frequencies

evidence for Place coding is  Tonotopic Maps on the Cochlea - an orderly progression of sensitivity from high to low. Hair cells and auditory nerves are also tuned to specific frequencies and Each nerve fiber has a preferred frequency (or characteristic frequency)

what is phase locking?

Phase locking:   a group of auditory nerve fibers fires so that the frequency of the waveform is coded by the ensemble - the output of any one fibre is ambiguous

What types of hearing loss is there and how to they occur?

Two types of hearing loss Conductive hearing loss and Sensorineural hearing loss

Conductive hearing loss

Blockage of sound from the receptor cells

Sensorineural hearing loss

Damage to hair cells

Damage to the auditory nerve or brain

Most common type is prebycusis

Presbycusis  is most common form of hearing loss (Sensorineural)  caused by exposure to damaging noises or drugs