Auditory sensation and perception

• transduction

  process where characteristics of a stimulus are converted nerve impulses
• Frank zappa definition for sound

  sound bounced around a medium and some of it bounces onto your ear- what you end up earing
• sounds consists of

  sounds waves- pressure waves travelling through any medium that will allow their conduction
• frequency

  number of sound waves, or cycles that occur per second
• amplitude

  vertical size of sound waves
• hertz

  technical measure of cycles per second
• decibels

  measure of physical pressures that occur on the eardrum
• human can detect frequencies from

  20 to 20,000 Hz
• Pinnae

  visible part of ear outside the head
• Pinnae function

  to collect and help localise where sounds are coming from- sounds hitting pinnae are; funnelled, amplified and directed into the auditory canal
• auditory transduction

  sounds waves travel to the eardrum- eardrum vibrates- middle ear houses three bones, there role is impedance matching
• three bones in middle ear

  hammer, anvil and stirrup (ossicles). role: impedance matching
• impedance

  effectively relates to how much a given medium impedes sound waves
• impedance of air and inner ear

  very low- so bones are there to protect inner ear from damage
• ossicles

  match the impedance of the air to the cochlea
• inner ear contains

  cochlea, coiled, fluid filled tube
• organ of Corti

  rests on basilar membrane: contains thousand of tiny hair cells that are the actual sound receptors
• pressure crated at oval window by middle ear bones set cochlea in motion

  fluid waves vibrate basilar membrane

  hair cells in organ of Corti bend- motion causes hair cells to fire
• hair cells firing

  triggers release of neurotransmitters; nerve impulses are sent to the brain, specifically the auditory cortex
• auditory system

  transforms wave amplitude and frequency into nerve impulses
• intensity

  high amplitude sound wavs cause hair cells to bend more; releases more neurotransmitter substance which causes auditory nerves to fire more frequently
• Frequency theory of pitch perception

  nerve impulses sent to the brain match the frequency of the sound wave; only works up to 1000Hz
• Place theory of pitch perception

  specific point in cochlea where fluid wave peaks and most strongly bend the hair cells- serves as a frequency coding clue- allows us to hear pitches above 1000Hz
• Sound Localization

  nervous system uses time and intensity differences of sounds arriving at the two ears to locate them:

  sound perceived first and loudest by closest ear

  ability to localise sounds is very sensitive

  pinnae and elevation
• conductive hearing loss

  problems with mechanical system that transmits sound waves to the cochlea

  can be helped with hearing aids
• Sensio neural hearing loss

  caused by damaged receptors in the inner ear or damage to auditory nerve

  does not respond to hearing aids

  caused by aging, disease and loud sounds
• sensory prosthetics

  device; provide input that can, to some extent, substitute for what cannot be supplied by the persons sensory receptors

  based on idea we hear with our brains, not our ears
• cochlear implants

  replace hair cells that are damaged in cochlea with electrical input

  behind ear- receive signals and translate into electrical signals

  those signals sent to the cochlea

  electrodes implanted inside cochlea take in electrical signals and breakdown frequencies- information then goes straight to brain

  can hear but muffled- takes brain time to adjust