3A. Hearing the World

• How do optical illusions demonstrate the difference between sensation and perception?

  They show that sensory information received by the brain is not always the same as what we perceive.
• What must happen to sensory signals before they can travel through the nervous system?

  They must be received by specific receptors and converted to nerve impulses.
• What role does previous experience and attention play in the perception process?

  They combine with sensory information to create a precept that informs understanding and behavioral response.
• What type of waves are sounds classified as?

  Longitudinal waves
• What does amplitude refer to in sound waves?

  It refers to the size of the fluctuations in the wave, with larger amplitude associated with louder sound.
• What is the range of sound intensity that humans can hear?

  0-140 dB
• What does frequency indicate in sound waves?

  It indicates the time in which the cycle repeats, with quicker repeats indicating a higher pitch.
• What is the range of frequencies that humans can hear?

  20 Hz to 20 kHz
• How is the ear structurally divided?

  The ear is divided into the outer ear, middle ear, and inner ear.
• What are the components of the outer ear?

  The outer ear includes the pinna, auricle, and external auditory canal.
• What separates the outer ear from the middle ear cavity?

  The tympanic membrane
• What is the function of the middle ear?

  The middle ear amplifies pressure created by sound waves to prevent loss as it enters the fluid-filled cochlea.
• What is acoustic impedance in relation to the middle ear?

  It is the function that amplifies pressure to prevent sound waves from bouncing back in the cochlea.
• What is the role of the stapes in the ear?

  The stapes is attached to the entrance of the cochlea and helps transmit sound waves into the inner ear.
• How does the outer ear assist in sound localization?

  It funnels sound inwards and helps localize sound in the vertical plane through the moveable pinna in some animals.
• What protective features does the outer ear have?

  It has water-resistant wax that is antibacterial and antifungal, and hairs that stop small particles from entering.
• What happens to sound waves as they enter the cochlea?

  Sound waves enter through the oval window via the ossicles, causing vibrations that travel through the cochlear fluids.
• What are the three main chambers of the cochlea?

  The scala tympani, scala media, and scala vestibule.
• Where are the inner hair cells located in the cochlea?

  They are located in the organ of Corti, which is on top of the basilar membrane in the scala tympani.
• What is the function of stereocilia in auditory transduction?

  Stereocilia are hair-like projections that help transduce sound waves into electrical signals.
• What is the tallest stereocilia called?

  Kinocilium
• How do stereocilia connect to each other?

  They are connected by tip links.
• What happens when stereocilia are disturbed by a sound wave?

  The mechanically-gated potassium channels open, allowing potassium to enter the cell.
• What is a receptor potential?

  A receptor potential is a change in the membrane potential within a sensory receptor caused by the influx of potassium.
• What triggers the release of glutamate in auditory transduction?

  The influx of calcium ions following depolarization of the cell.
• What is the role of the auditory nerve in the auditory pathway?

  The auditory nerve is the post-synaptic cell where glutamate binds to AMPA receptors, producing an action potential.
• What happens to the information encoded in the cochlea?

  It is turned into an electrical signal and transmitted to the primary auditory complex through the auditory pathway.
• What are the steps in the auditory pathway from the cochlea to the brain?

  1. Signal sent from cochlea to cochlear nuclear complex.
  2. Signal sent to the superior olivary complex for sound localization.
  3. Signal reaches the inferior colliculus in the midbrain.
  4. Signal arrives at the medial geniculate nucleus in the thalamus.
  5. Finally, it reaches the primary auditory cortex.
• What information do we use to determine 'what' and 'where' a sound is?

  We use information about frequency and intensity to determine 'what' a sound is, and distance and direction to determine 'where' it is.
• What are the two theories of frequency coding in the cochlea?

  1. Place theory:

  • Specific hair cells respond to specific frequencies.
  • High frequencies at the basal end, low frequencies at the apical end.

  1. Temporal or rate code:

  • Hair cells oscillate to the frequency of the incoming sound.
  • Action potentials in the auditory nerve map onto the frequency of the sound.
• How does intensity coding occur in the cochlea?

  Intensity coding occurs through the firing of the auditory nerve and the number of neurons firing in response to sound amplitude.
• What are the methods of location coding in humans?

  • Vertical location coding is done by the pinna.
  • Horizontal location coding is done by the super olivary complex using:
  • Interaural intensity differences.
  • Interaural time delays.
  • Other intensity cues.
• What are the two streams of information processed beyond the auditory cortex?

  1. Posterodorsal stream: processes 'where' information.
  2. Anteroventral stream: processes 'what' information.