space and sound

• Physiology


  The study of the normal function of living organisms and their component parts
• Physical stimulus


  A stimulus that is physical in nature, such as sound or light
• Stimulus for sound


  1. Vibration of air molecules

  2. Cause neighbouring air molecules to vibrate (ripple effect)

  3. Entire experience of music, speech etc. is just vibration of air molecules
• Pure tones


  Described by 2 aspects of sound: frequency and amplitude
• Frequency


  The rate of air pressure modulation, number of cycles in a second
• Pitch


  Related to the frequency of sound
• Amplitude


  Changes in sound pressure level
• Loudness


  Related to the amplitude of sound
• 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

  1. Different frequencies of air pressure bash different hair cells depending on their location

  2. Different areas code for pure tone (sine wave)

  3. High frequencies activate beginning (don't hit hair cells at the end)

  4. Low frequencies activate end (hit hair cells at the end)

  
• 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

  
• Stream segregation


  1. Spectral separation

  2. Temporal separation

  3. Temporal onsets and offsets

  4. Spatial separation

  5. Temporal modulations
• Stream grouping


  • Similarity: pitch
  • Proximity: timing
  • Good continuation
  • Common fate: timbre
• We can only attend to one stream at a time (hear different song every time if you pay attention to a different stream)