Biological - Eyes and Ears Flashcards
What are the functions of hearing?
Hearing involves constructing a
model of the world:
– What objects do the sounds correspond to?
– Where are they?
– What do they mean?
▪ In noisy environment, many sounds overlap in time
– The brain needs to use
incoming sensory input and prior knowledge about sounds to understand them.
Describe the outer and middle ear.
▪ The outer ear (= pinna)
– captures the sound and amplifies it by funneling it into the smaller auditory canal
▪ The middle ear
– the eardrum collects the vibrations
* we can detect sound when the eardrum vibrates as little as the diameter of the hydrogen atom (Wilska 1935)
– the eardrum transmits the vibration
to the ossicles (3 small bones:
hammer, anvil & stirrup) transferring
vibration to the cochlea.
Describe the inner ear.
- Hearing - > cochlea -> translates
pressure to bioelectrical activity
and sends to upper structures in
the nervous system - Body balance -> vestibular
system: With each rotation, with the movement of endolymph, the hair cells undergo either depolarization or hyperpolarization, depending on
whether the endolymph moves them toward or away. - semicircular canals – detect
rotations - otolith organ – detects
acceleration. Hair cells in the utricle
& ear stones.
Describe the auditory pathway.
1) Sound in ear, auditory nerve sends information to same side as ear.
2) The first relay: ipsilateral (same side as ear) cochlear
nuclei in the brain stem, which receive input from the auditory nerve; some decoding of the signal duration, intensity and frequency occurs here.
3) The second relay in the brain stem - in the superior olivary nucleus (pons). The majority (but not all!) of the auditory fibres are contralateral.
4) The third relay takes place in the
inferior colliculus of the midbrain.
5) A final relay, before the cortex,
occurs in the thalamus (medial
geniculate body).
6) Projection from the thalamus to
the auditory cortex.
Define intensity, loudness, frequency, pitch.
Intensity: how much air fluctuation (compression/rarefaction) the sound creates, i.e., the energy in the sound. (amplitude).
Sound intensity is measured in decibels. Logarithmic scale.
Loudness is a subjective value which correlates with the objective intensity.
Frequency: number of air compression/rarefaction cycles
per second that the object creates.
A perceptual correlate of frequency (no one-to one
correspondence): pitch
The Place code (discovered by Georg von Békésy)
– Different places along the cochlea respond to different sound
frequencies because of differences in stiffness/elasticity of the
cochlear membrane (the outside edge is 100 stiffer then the central
end) – ‘tonotopic organisation’
– Each frequency has its designated path from the cochlea to the brain. Tonotopic organisation in the primary auditory cortex.
Describe the dichotic listening task.
Dichotic listening - a behavioural method to evaluate ear/
hemisphere dominance for speech.
Different syllables presented simultaneously, each to a different ear.
The ear contralateral to brain hemisphere dominant for speech gives more responses.
Brain lateralisation for auditory processing.
Right ear dominance for speech recognition – more connections
to the left brain hemisphere.
Speech - left hemisphere
music - right hemisphere
Both the sex and the handedness of the listener is related to
laterality.
Male participants show more asymmetry in performance of tasks
related to language and speech processing than their female
counterparts.
Right handedness – 95% language – Left hemisphere
Left handedness – 70 % language – Left hemisphere
prosodic aspects of
speech (production and
understanding) right hemisphere.
What is conductive hearing loss?
▪ Results from damage to the eardrum or ossicles in the
middle ear → failure to transmit sound waves to the (intact)
cochlea.
▪ Corrected by medication, surgery or by sound amplification
from hearing aids, or by using bone conduction.
How do bone conductivity hearing aids work?
▪ The sound is used to
vibrate the mastoid bone → the cochlea receives the vibrations, turns
them into the electric signals &
passes to the auditory nerve.
What is sensorineural hearing loss?
▪ Damage to (part of) the cochlea/hair cells in the inner ear.
▪ Congenital, result of a disease or repeated exposure to loud
noises.
▪ Corrected by cochlear implants, a surgically implanted electronic device which receives a sound signal via a microphone and conducts
is via thin wires to directly stimulate the auditory nerve.
