space and sound

• Vibration of air molecules causes neighbouring air molecules to vibrate (ripple effect)
• Pure tones are described by 2 aspects of sound: frequency and amplitude
• Frequency


  The rate of air pressure modulation; number of cycles in a second; related to pitch: high or low
• Amplitude


  Changes in sound pressure level; related to loudness

  
• Transduction


  1. Air pushes on eardrum (or tympanic membrane)

  2. Connected to 3 little bones (maleus, incus, stapes), which act as amplifier, increasing pressure on cochlea

  3. Shake cochlea
• Cochlea

  • Fluid filled membrane with hair cells inside
  • If fluid moves, certain hair cells bash against tectorial membrane (solid cell layer in center of cochlea)
  • Bending of hair cells causes action potential
• Frequency coding in cochlea

  • Different frequencies of air pressure hit different hair cells depending on their location
  • High frequencies hit at the beginning
  • Low frequencies hit at the end or apex
• Organ of Corti


  Where hair cells are hit
• Cochlear implant


  Stimulates auditory nerve where the hair cell would have been (because hair cells don't regenerate)

  
• Audition wears out with old age because it's a mechanical system
• Many animals have much better auditory systems than humans
• Moles

  • Good hearing with low frequencies because that's the sound that travels underground
• Dolphins

  • Good for high frequencies because the sounds they make when they communicate
• Auditory streams

  Complex sounds made up of several different frequencies from several different sources (leading to auditory gestalts)
• Stream segregation


  1. Spectral separation

  2. Temporal separation

  3. Temporal onsets and offsets

  4. Spatial separation

  5. Temporal modulations --> changes in loudness and pitch
• Stream groupingSimilarity: pitch

  • Similarity: pitch
  • Proximity: timing --> frequencies that are closer together are grouped together (we presume they come from the same object)
  • Temporal proximity --> sounds closer in time typically come from same object
  • Good continuation --> when loud sound is played over another sound, we presume it goes on behind the louder one (filling gaps)
  • Common fate: timbre --> progression (onset and offset) of sound
• We can only attend to one stream at a time