Chapter 6

• What is the role of the human sense of taste?


  It alerts us to the bitterness of poisons.
• Why do our olfactory systems not respond to certain gases?


  They are unresponsive to gases that we don’t need to detect.
• What is the focus of Chapter 6?

  • How our sensory systems process biologically useful information.
• Under optimum conditions, how sensitive is human hearing?


  It can detect sounds that vibrate the eardrum by less than one-tenth the diameter of an atom.
• What is the smallest difference in sound that humans can detect?


  Humans can detect a difference as little as 1/30 the interval between two piano notes.
• How do we use hearing to extract useful information?

  • Hearing footsteps indicates someone is nearby.
  • Hearing breathing suggests proximity to a person or animal.
  • Recognizing a familiar voice reassures us.
• What are sound waves?


  • Periodic compressions of air, water, or other media.
  • Vary in amplitude and frequency.
• What does amplitude refer to in sound waves?


  Amplitude refers to the intensity of a sound wave.
• How does amplitude affect our perception of sound?


  Sounds with greater amplitude seem louder.
• What is the frequency of a sound wave?


  Frequency is the number of compressions per second, measured in hertz (Hz).
• How do higher frequency sounds differ from lower frequency sounds?


  Higher frequency sounds have more compressions per second and are perceived as higher-pitched.
• What is pitch in relation to sound?

  Pitch is the perception of how high or low a sound is, related to frequency.
• What is the typical hearing range for adult humans?


  Most adults hear sounds starting at about 15 to 20 Hz and ranging up to almost 20,000 Hz.
• Why do children hear higher frequencies than adults?

  Because the ability to perceive high frequencies decreases with age and exposure to loud noises.
• How do hearing abilities differ between larger and smaller animals?


  Larger animals like elephants hear best at lower pitches, while smaller animals like mice hear higher pitches.
• What does timbre refer to in sound?


  Timbre refers to the tone quality or tone complexity of a sound.
• How can you differentiate between a piano and a violin playing the same note?


  The difference is due to timbre, which makes different sounds unique despite having the same pitch and loudness.
• What are the main structures of the ear and their functions?

  • Outer Ear: Includes the pinna, which captures sound waves.
  • Middle Ear: Contains the tympanic membrane and three tiny bones (hammer, anvil, stirrup) that transmit vibrations.
  • Inner Ear: Contains the cochlea, which converts vibrations into electrical signals.
• What is the function of the pinna in the outer ear?


  The pinna helps to capture sound waves and direct them into the auditory canal.
• What connects the tympanic membrane to the oval window in the middle ear?


  The tympanic membrane connects to three tiny bones: hammer, anvil, and stirrup.
• How do vibrations of the tympanic membrane affect sound waves?


  The vibrations amplify into more forceful vibrations of the smaller stirrup, converting sound waves into waves of greater pressure.
• What happens when the stirrup vibrates the oval window?


  It sets into motion the fluid in the cochlea.
• What are hair cells in the cochlea responsible for?


  Hair cells convert movements into electrical signals that the brain interprets as sound.
• What is the process of sound wave transmission in the ear?

  1. Sound waves strike the tympanic membrane.
  2. Vibrations are transmitted through the hammer, anvil, and stirrup.
  3. Vibrations convert into stronger vibrations in the cochlea.
  4. Hair cells in the cochlea displace and send signals to the brain.
• How does pitch perception work?


  It depends on the ability to differentiate among sounds of different frequencies.
• What are the three theories of pitch perception?

  1. Place Theory: Different frequencies activate hair cells at specific locations.
  2. Frequency Theory: The entire basilar membrane vibrates in synchrony with sound.
  3. Volley Principle: Auditory nerve produces volleys of impulses for sounds up to about 4000 Hz.
• What is the downfall of Place Theory?


  Various parts of the basilar membrane are bound together too tightly for any part to resonate like a piano string.
• What is the downfall of Frequency Theory?


  The maximum firing rate of a neuron is about 1000 Hz, which is far short of the highest frequencies we hear.
• How does the Volley Principle work?


  The auditory nerve produces volleys of impulses for sounds up to about 4000 per second.
• How do soft and strong sounds affect neuron activation?


  Soft sounds activate fewer neurons, while stronger sounds activate more neurons.
• How do high-frequency sounds affect hair cells in the cochlea?


  High-frequency sounds excite hair cells near the base of the cochlea.
• How do low-frequency sounds affect hair cells in the cochlea?


  Low-frequency sounds excite hair cells farther along the membrane.
• How do we perceive low-frequency sounds?


  At low frequencies, the basilar membrane vibrates in synchrony with the sound waves.
• How do we perceive middle-frequency sounds?


  At intermediate frequencies, different axons fire for different waves, creating a volley of axons for each wave.
• How do we perceive high-frequency sounds?


  At high frequencies, the sound causes maximum vibration for the hair cells at one location along the basilar membrane.
• What is the organization of the auditory cortex?


  • Anterior temporal cortex: Identifies sounds.
  • Posterior temporal and parietal cortex: Locates sounds.
  • Organized similarly to the visual cortex.
• What happens to auditory information in the midbrain?


  Information from the auditory system crosses over, allowing each hemisphere to receive input from the opposite ear.
• What is the primary auditory cortex (area A1) responsible for?


  It is essential for processing auditory information and is located in the superior temporal cortex.
• How does damage to the primary auditory cortex affect hearing?


  It does not cause deafness but affects speech and music processing.
• What is a tonotopic map in the auditory cortex?


  It is a map where cells responsive to similar frequencies group together.