Audition: Hearing ( Exam 3 )

Sound

air pressures variations over time
- high to low pressure
- speed ~ 760 mph (light = 670,000,000 mph)

thunder and lightning

a loud crashing noise heard after lightning
- a great example of the properties of sound and light

Frequency

cycles per second
- measure: Hertz (Hz)
- pitch
- humans: 20 to 20,000

Amplitude

pressure wave height
- loudness
- measure: decibels (dB)

Ear Structures

outer ear, middle ear, inner ear

Outer Ear

- directs sound into the ear for processing
- Pinna (auricle)
External Auditory Canal

external auditory canal

The ear canal; leads to the tympanic membrane.

tympanic membrane (eardrum)

vibrates in response to sound waves
- seals middle ear

Microtia

abnormally small pinna

Anotia

absence of pinna

aural atresia

congenital absence of the external auditory canal

Auricular Hematoma (Cauliflower Ear)

a compress or shearing injury that causes subcutaneous bleeding. to prevent wear protective head gear. most common in wrestling

Middle Ear

- amplification of sound (for air to fluid shift)
- 3 Ossicle bones
- Eustachian Tube
- Muscles

ossicles of middle ear

malleus (hammer; attached to eardrum)
incus (anvil)
stapes (stirrup; attached to oval window)

Eustachian tube

A narrow tube between the middle ear and the throat that serves to equalize pressure on both sides of the eardrum
- maintains balance of air pressure in middle ear
- outer and middle ear must have same pressure for optimal hearing
- drainage system for infections

Muscles of the middle ear

tensor tympani and stapedius

tensor tympani

the muscle attached to the malleus; tensing the tensor tympani decreases vibration

stapedius

the muscle attached to the stapes; tensing the stapedius decreases vibration

otosclerosis

hardening of the bony tissue of the middle ear
- stapes can no longer move
- lose ability to hear low frequencies
- Treatment: Hearing aid, stapes replacement (stapedectomy)

Hearing Aids

- amplify sound
- newer, digital aids are programmable
- adaptable to individual's needs (e.g, particular frequencies in need of boost)
- effective for those with cochlear function

Inner Ear

- fluid-filled
- Structure: Cochlea ("snail")
a. oval window
b. round window
c. Basilar Membrane

oval window

the membrane that separates the middle ear from the inner ear (end of cochlea)

round window

other end of cochlea, moves opposite the oval window

basilar membrane

- surface moves in a wave-like fashion
- near oval window it is narrow and more rigid
- becomes wider and more flexible farther into cochlea
- structure determines location/max. frequency relationship

Organ of Corti

Center part of the cochlea, containing hair cells, canals, and membranes
- site of transduction
- hair cells contact tectorial membrane
- causes depolarization of cell, and signal
- peak of wave= strongest signal, information about sound

presbycusis

age-related hearing loss
- damage to hair cells in Organ of Corti
- damage begins closer to oval window (high frequencies lost)

tinnitus

ringing or buzzing in the ears
- signal from cochlea without external stimulus
- "phantom sounds"
- not well understood (cause, treatment)

Cochlear Implant

- for those with no cochlear function
- external sound processor and transmitter (attached to side of head)
- internal receiver and electronic "cochlea"
- must learn to interpret these "sounds"
- not like typical hearing

Newborn Screening Test

- for congenital hearing loss

Otoacoustic Emissions Test (OAEs)

-measure sound coming out of the ear; reflecting off internal structures

Auditory pathway to the brain

Cochlea output = auditory nerve
- 3 (pre-thalamus) nuclei
1. cochlear nucleus
2. Superior Olivary Complex
3. Inferior Colliculus
4. must processing occurs at these basic levels (much more so than in vision)
c) Medial Geniculate Nucleus (of thalamus)
d) projected to Primary Auditory Cortex (in temporal lobe)

superior olivary complex

a structure in the brain stem (one on each side of the brain); a stop on the ascending auditory pathway receiving signals from both cochlear nuclei

Inferior Colliculus

a midbrain nucleus in the auditory pathway
(eye movement)

medial geniculate nucleus (MGN)

the part of the thalamus that relays auditory signals to the temporal cortex and receives input from the auditory cortex

Cortical Processing

1. areas in brain respond differentially to particular frequencies
2. similar to basilar membrane mapping
b) most frequency information is place coded
c) low frequencies are partially temporally coded (phase locking; cells working as groups)

tonotopic mapping

The coding of frequency to a specific place along the basilar membrane

phase locking

Firing of auditory neurons in synchrony with the phase of an auditory stimulus.

sound localization

determining the location of the source of sound
- similar to depth perception
- monaural cues vs. binaural cues

Monaural cues (one ear)

Pinna-based
- particular shape of pinna determines frequency analysis
- sounds from different locations = different patterns
- most effective for sound elevation changes

binaural cues

cues sound location that requires both ears
- Interaural Time Difference (ITD; left/right primarily)
- Interaural Intensity Difference (IID; best for high frequencies)

interaural time difference (ITD)

the difference in arrival time of the same sound at the two ears

Interaural Intensity Difference (IID)

the difference between signal intensity levels at each ear

Echolocation

produce sound and code echoes of sound off objects

Echolocation in bats

1. uniquely shaped, movable pinnae
2. mammalian auditory system (similar structurally to humans)
3. sounds produced from vocal tract (e.g., larynx, tongue; 20,000+ Hz)
4. Echolocation behaviors
a. head movements to sample environment
b. pulse frequency varies (e.g., speeds up when nearing target)

used to guide movement, identify obstacles, and find food

Can humans echolocate?

1. evidence that some people can learn to echolocate
2. most common in those who are blind
3. limited range (~2 feet)
4. likely plasticity based (e.g., early blind most likely to develop ability)