final exam

• Auditory brain


  • Neural signals from cochlea carry information about sound to the brain via auditory nerve
  • Signals processed and combined with other senses as they travel via ascending pathways from brain stem to auditory areas in cerebral cortex
  • Feedback signals from brain travel back to cochlea via descending pathways

  
• Key brain structures


  • Cochlear nucleus
  • Inferior colliculus
  • Medial geniculate body
  • Superior olivary complex
• Descending pathways


  1. From auditory cortex to subcortical auditory structures and ears

  2. Involved in attention - block task-relevant signals

  
• Auditory cortex


  • Part of cerebral cortex, tucked into lateral sulcus on temporal lobe
  • Consists of auditory core region, belt, and parabelt
  • Tonotopic organization continues in primary auditory cortex (A1)

  
• Tonotopic map


  Arrangement of neurons within auditory brain regions such that characteristic frequencies gradually shift from lower to higher

  
• Frequency tuning of neurons

  • Can be broad or narrow
  • Narrowly tuned neurons only respond to narrow band around characteristic frequency
  • Broadly tuned neurons respond to wider band as amplitude increases

  
• "What" and "Where" pathways

  • "What" pathway specialized for representing identity of sound sources, extends from core to belt/parabelt and anterior temporal cortex
  • "Where" pathway specialized for representing location of sound sources, extends from core to posterior auditory cortex and posterior parietal cortex

  
• Auditory system uses comparison of sound at two ears to localize sound sources, unlike vision which uses retinotopic representation

  
• Azimuth


  Location of sound source in side-to-side dimension in horizontal plane

  
• Elevation


  Location of sound source in up-down dimension in median plane

  
• Distance


  How far sound source is from centre of head in any direction

  
• Minimum audible angle


  Minimum angular separation between reference and different sound source that yields 75% correct judgments about relative horizontal positions

  
• Acoustic shadow


  • Area on other side of head from sound source where loudness is reduced due to partial blocking by head
  • Has greater effect on high-frequency sounds

  
• Interaural level differences (ILDs)


  Difference in sound level of same sound at two ears

  
• Interaural time differences (ITDs)


  Difference in arrival time of same sound at two ears

  
• Cone of confusion


  Hypothetical cone-shaped surface in auditory space where multiple sources have same ILD and ITD
• Head motion disambiguates azimuth by changing ILDs and ITDs
• Fusion


  • Their locations are confusable because they have highly similar ILD and ITD
• Pinnae (outer ear)


  Reduces the cone of confusion
• Spectral shape


  The sound changes depending on the direction of the source

  
• As soon as you turn your head one side or the other or tilt it to the left or right

  The ILD and ITD of the sound changes in a way that instantly disambiguates the azimuth of the source

  
• A sound source located directly in front of the listener


  Produces the same ILD and ITD as a source directly behind the listener

  
• If the listener rotates his head to the left

  The ILDs and ITDs will change in a way that depends on the true location of the sound source

  
• Virtual Barbershop


  1. D hearing can be created much like 3D- movies/stereoscopes can simulate 3D vision
• Binaural recording


  Simulates ITDs and ILDs
• ASMR


  Autonomous Sensory Meridian Response - Soft tingling sensation often occurs to sounds of whispering or other soft noises
• ASMR is a relatively new field of study
• ASMR may involve activation of insular cortex - Monitoring internal states/pain
• Sakurai et al., (2023) increased insula activity
• Relative intensity


  The largest cue to distance
• The sound localization cues - ILD, ITD, and the spectral shape cue provide little information about distance

  
• If the listener knows the sound level of the source

  The perceived loudness can be used to judge at least whether the source is relatively near or far

  
• The amplitude of a sound decreases in proportion to the square of the distance to the source

  
• Air absorbs high frequency sounds more than low frequency sounds
• Relative amount of direct vs reverberant energy

  Sounds bounce (reverberate) off surfaces, this energy takes longer to arrive than direct energy, differences are perceptually cancelled
• Echoes in situations where are many hard surfaces to reflect sound waves

  An important cue for distance

  
• Spectral shape cue


  A pinna-induced modification in a sound's frequency spectrum; provides information about the elevation of the sound source

  
• Loudness cue


  As a sound source approaches a listener, the loudness increases, and as the source recedes from the listener, the loudness decreases

  
• Doppler Effect


  The frequency of a sound emitted by a moving sound source is higher in front of the sound source than behind it, the frequency rapidly decreases as the sound source passes the listener

  
• Auditory scene


  All the sound entering the ears during the current interval of time