2017-04-09 06:35:59

Prelude

Today's Topics

  • Auditory processing

Auditory processing

  • Goals
    • What's out there
    • Where is it?
  • Sound
    • What is it?
  • How the brain processes sound

What is sound?

  • Sound = pressure waves
  • Vary in frequency, amplitude
  • Requires a physical medium
  • Works in the dark, over long distances, out of sight lines

Alien

Detecting sound

Outer ear

  • Pinnae
    • Filter sound
    • Channel sound
  • Ear canal
    • Resonates to frequencies in speech

Length, diameter determine resonant frequency

Middle ear

Middle ear

  • Tympanic membrane
  • Ossicles
    • Malleus ('hammer')
    • Incus ('anvil')
    • Stapes ('stirrup')
  • Middle Ear Muscles
    • Stapedius & tensor tympani

Where are we

Function of ossicles, stapedius

  • Ossicles amplify
    • Air thinner than cochlear fluid
  • Muscles dampen
    • Acoustic reflex when sound intense or speaker vocalizes

Inner ear

Inner ear

  • Oval window
  • Cochlea
    • Organ of Corti
  • Round window

Organ of Corti

Organ of Corti

  • Basilar membrane
  • Tectorial membrane
  • Hair cells
  • Cochlear fluid/endolymph

Hair cells

  • Inner hair cells
    • Transduce pressure waves
  • Outer hair cells
    • “Fine tune” transduction
    • Alter stiffness of basilar/tectorial membranes

Otoacoustic emissions (OAE)

  • Sounds made by the ear
    • Reflect integrity of hair cells
  • Age of detection critical for early therapy

Standing waves

Cochlear movement

CNS projections

CNS projections

  • Auditory nerve (8th/XIII cranial)
  • Cochlear nuclei
  • Superior olivary nucleus
    • L & R ear inputs mix
  • Inferior colliculus

CNS projections

CNS projections

  • Thalamus
    • Medial geniculate nucleus (MGN)
  • Temporal lobe
    • Auditory Cortex (AI)

Coding frequency

  • Frequency ~ pitch
  • Mixture of frequencies ~ timbre (TAHMber)
  • Place code
    • Place on basilar membrane that vibrates most strongly

Place code

Place code ~ xylophone

Tonotopy

Tonotopy in auditory cortex

Timbre

Perceiving location

Perceiving location

  • Interaural (between the ears) time/phase differences
    • Low frequencies
  • Interaural intensity differences
    • High frequencies

How do we perceive sound elevation?

Next time…

  • Vision