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Perception 4
Audition - Coggle Diagram
Perception 4
Audition
Functions of
Hearing
- auditory perception is the ability to identify and localise the sound signals in the environment.
- functions of hearing:
- detection and identification of signals in the environment
- speech perception
- music perception
- sound localisation
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Auditory
Physiology
- the transduction of sound wave energy into the nerve impulses occurs in the inner ear which is filled with fluid that is much denser than air.
- pressure changes in air transmit poorly into the denser medium so the sound stimulus needs to be amplified for better transmission to the fluid.
- the amplification is accomplished by the accessory structures in the outer and middle ear.
outer ear
- sound waves are funnelled into the ear
- resonate in the auditory canal (the site of amplification)
- waves make the eardrum move/vibrate
middle ear
- eardrum vibration affects the bones in the middle ear (ossicles)
- eaves amplified again by ossicles
- the stirrup vibrates against the oval window membrane between the middle and inner ear
inner ear
- stirrup vibration of the oval window membrane affects fluid in the cochlea
- the movement of the cochlear fluid stimulates the auditory receptors (hair cells) which transduce mechanical into neural energy
sensory code for pitch perception
- two ways in which pitch information can be encoded
- which hair cells are stimulated: specific groups of hair cells are sensitive to a specific frequency and, in turn, activate a specific set of auditory nerve fibres.
- "place code" for pitch perception > tonotopic organisation > tuning of different parts of the cochlea to different frequencies.
- hair cells are sensitive to different auditory frequencies and are orderly arranged along the basilar membrane.
- the information about the particular frequency of an incoming sound wave is coded by the place in the cochlear with the maximal response.
- how auditory nerve fibres are firing: rate (or pattern) of the firing of nerve impulses to specific auditory frequencies.
- frequency matching theory:
- information about the particular frequency of an incoming sound wave is coded by matching the frequency of neural firing
- one potential problem for this theory is that no neurons can fire faster than 1000Hz (but we have a sensitivity of 1000-5000Hz)
- the volley principle (population coding): an idea stating that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire every period.
hearing and ageing
- hearing loss: a natural consequence of ageing or due to damage or disease;
- young people: range of 20-20,000 Hz
- by college: range of 20-15,000 Hz
- hearing aids: earliest devices were horns; today, electronic aids.
- primary auditory cortex:
- tonotopic organisation: systematic progression in frequency preference across the cortical surface.
- seen in the primary auditory cortex as well as the cochlear
- over-representation of frequencies in the middle of the audible spectrum
- sensitive to voices
- secondary auditory areas > specialisation areas
- broca's area and wernicke's area
- damage leads to an inability to produce and/or understand language
Sound
Localisation
what and where streams for hearing
- what (or ventral stream): located in the temporal lobe, responsible for identifying sounds
- where (or dorsal stream): located in the parietal and frontal lobes, is responsible for locating sounds
auditory localisation
- refers to the ability to determine where in space a sound originates.
interaural timing differences
- a sound wave coming from the side will hit the nearer ear first, creating a time lag between the two ears.
- perception of the sound's location depends on the sound that reaches the ear first.
- does not apply if the sound source is directly above, to the front, or behind, because both ears will hear it at the same time.
the precedence effect + indirect sound and echo suppression
- the psychoacoustic phenomenon whereby an acoustic signal that arrives first at the ears suppresses the ability to hear any other signals, including echos and reverberation of that signal that arrives up to about 40ms after the initial signal
- provided that the delayed signals are not significantly louder than the initial signal.
- a signal arriving after a delay of 40-50ms is heard as an echo.
- direct sound: the sound reaching the ears directly
- indirect sound: the sound reaching the ear after being reflected by different objects or surfaces.
- cones of confusion: there are multiple locations on each side of the head which produce identical Interaural Time Differences and Interaural Loudness Differences.
spectral cues from the filtering properties of the pinna
- to disambiguate the cones of confusion, we make use of the filtering properties of the pinna
interaural intensity differences
- for certain directions of the sound source, the head creates acoustic shadow, reducing the sound intensity on once side.
- if the sound is in front of you, both ears will hear it at the same intensity, but if it's on your right side, your right ear will hear it at a higher intensity than your left.
- the intensity differences can be substantial for high-frequency sounds but are negligible for low frequencies, whose wavelenghts are on order of the width of the head.