Task 7: Auditory system Flashcards
Sound stimulus (physical)
movements of vibrations of object cause pressure changes in air, water or any other elastic medium that surrounds objects
Sound perception
experience when we hear
Sound wave
pattern of alternating high pressure (condensation) and low-pressure (refraction) regions in the air
A sine wave’s or a pure tone’s vibration can be described by its
frequency and amplitude
Frequency
- number of cycles per second that pressure changes repeat
- associated to pitch (higher frequency = higher pitch)
- Hz
Amplitude
- difference in pressure between high and low-peak of sound wave
- associated with the quality of sound = loudness
- dB
Complex tones
sounds produced by instruments or people speaking that have a more complex sine wave’s pattern
A complex tone is made up of
a number oh harmonics and fundamental frequencies added together = Fourier analysis
Fundamental
first harmonic
Fundamental frequency
- lowest frequency component
- repetition rate
Perceptual aspects of sound
- threshold
- loudness
- pitch
- timbre
High threshold
large sound pressure changed required
Low threshold
little sound pressure change required
Loudness
- intensity of a sound
- depends on amplitude and frequency
Audibility curve
threshold of hearing
- we cannot perceive sounds lower the audibility curve
Threshold for feeling
- upper curve
- sound that are higher than the upper curve provoke pain
Equal loudness curve
same perception of loudness at different frequencies
Pitch
- linked to fundamental frequency
- high or low label
Tone height
perceptual experience of increasing pitch that accompanies increases in tone’s fundamental frequency
Notes with the same tone have
the same tone chroma
Effect of missing fundamental
pitch remains the same even if fundamental or other harmonics are removed, therefore pitch depends on the repetition rate and not on the fundamental frequency
Timbre
tones that have the same loudness, pitch and duration but still sound different
Steady-state harmonic structure states that
- same fundamental => same pitch
- different amount of harmonics => different timbre
Structure of the ear
- outer year
- middle year
- inner year
Outer ear
- pinae = determine location of sounds
- auditory canal = protects middle year, enhances the intensities of some sounds by resonance and reinforces sound frequency
- tympanic membrane = set sound waves into vibrations
Middle ear
- fluid medium => transmission of sound vibration from air to middle ear is difficult, therefore
1 - ossicle increase pressure
2- ossicle is hinged to create lever action
Ossicles
responsible for amplification of sound (maleus, incus and stapes)
Inner ear
vibration of oval window => vibration of fluid inside the cochlea
Cochlea
- main structure of inner ear
- contains Organ of Corti
- scala vestibuli =upper half of cochlea
- scala tympani = lower half of cochlea
- cochlear partition separated the s. vestibuli and s. tympani
Apex of the Cochlea is
the basilar membrane => movement of basilar membrane exerts force on cilia agains tectorial membrane
Organ of Corti
- sits on the basilar membrane
- contains hair cells and cilia
Hair cells are the
receptors for hearing
Tectorial membrane
Area that arches over the hair cells
Cilia
top of hair cells
Hair cells
Vibration from the basilar membrane and tectorial membrane bends the:
- inner hair calls
- outer hair cells => tallest row of cilia on outer hair cells
Vibrations of liquids inside cochlea re translated into waves in the
basilar membrane => up and down motion of the basilar membrane
Up and down motion of the basilar membrane results in
- Organ of Corgi - up and down vibration
2. Tectorial membrane - back and forth vibration
Transduction
movement of hair cells => transmitter release => action potential
Back and forth bending of the cilia triggers
sequence of chemical reactions
- movement to right => tip links stretch = increase in pressure => release of neurotransmitters
- movement to the left => tip link slacken => firing stoped
Tonotopy in Cochlea
- hair cells are activated at different frequencies and places along cochlea
- higher frequency = base of cochlea
- lower frequency = apex
Characteristic frequency
frequency to which a particularly auditory nerve fibre is most sensitive
Auditory masking
- perception of one sound is affected by the presence of another sound
- effect of masking is stronger from low to high
Temporal code
a frequency is code by the timing of neural firing
Coding of frequency
- by place (tonotopy at the level of neurons)
- by time (level of auditory nerves) => phase locking
Phase locking or volley principle
each neuron fires at a distinct point an not on every point => provide temporal code
Each neuron gives an optimal response to
a preffered stimulus and a less strong response to stimuli that deviate from the preferred one
Primary central auditory pathway
Cochlear nucleus -> Superior olivary nucleus (converge inout from both ears) -> inferior colliculus -> medial geniculate nucleus -> primary auditory cortex
Primary auditory cortex
- responsible for processing acoustic information
- consists of A1, belt and parabelt area (complex sounds)
Hearing loss
elevation of sound thresholds
Types of hearing loss
Conductive
Sensorineural
Hidden
Conductive hearing loss
- impairment to amplify sound
- lost ability of middle-ear bones to convey vibrations from tympanic membrane to oval window
Sensorineural hearing loss
- damage in cochlea and hair cell (prebyscusis)
- hearing loss at high frequencies
Hidden hearing loss
harder to hear sounds when there is background noise
Treating hearing loss
- Cochlear implant
- Auditory brainstem implant
Cochlear implant
- stimulates the auditory nerve
- amplifies sound
Auditory brainstem implant
- micro electrode that stimulates brainstem
- no auditory nerve lesions
Doubling sound pressure leads to
doubled perceived loudness
