Hearing

The Ear

Outer Ear

• Pinna: captures sound and channels it into ear canal
• Ear Canal: “carries” sound towards inside of ear
• Ear Drum: vibrates at the same frequency of the sound

Middle Ear

• Ossicles
  • 3 bones: Hammer (Malleus), Anvil (Incus), Stirrup (Stapes)
  • In contact with the eardrum → vibrate at the same frequency as the eardrum

Inner Ear

• Cochlea: fluid-filled coiled tube
  • Oval window (membrane) makes contact with stirrup → vibrates with the same frequency
  • Basilar membrane ripples with the same frequency as sound
  • Hair cells sway with same frequency as sound
    • Synapses with neurons that form the auditory nerve
    • Goes to thalamus then temporal nerves

Hearing

• Stimulus: sound waves
• Pitch: frequency
  • related to wavelength
  • Hertz (Hz): cycles per second
  • Shorter wavelength → higher frequency, higher pitch

  Frequency Theory

• Basilar membrane in cochlea vibrates at the same frequency as sound → hair cells transmits information that brain interprets

  Place Theory

• Different parts of the basilar membrane vibrate for different frequencies
  • Intensity (volume): amplitude
• Low amplitude → low volume
• Decibels

Hearing Loss

Conduction Hearing Loss

• Outer, middle ear
  • Eardrums, ossicles, etc.

Sensorineural Hearing Loss

• Hair cells
• Auditory nerve
• Congenital or acquired (due to loud noises, old age, etc.)

Binaural cues

• Allow sound localization
• Sound arrives at two ears at different times → each ear “hears” a different volume → used by brain to localize the sound