17.6 Hearing

Sound perception is a fascinating interplay of physics and biology. Our ears and brain work together to interpret sound waves, allowing us to distinguish pitch, loudness, and timbre. These qualities help us navigate our auditory world, from enjoying music to locating danger.

The ear's intricate structure transforms sound waves into neural signals. From the outer ear to the cochlea, each part plays a crucial role in processing sound. This complex system enables us to locate sounds in space and interpret complex auditory information.

Sound Perception

Key terms in sound perception

Top images from around the web for Key terms in sound perception

• 

  Frequency, Wavelength, and Pitch ‹ OpenCurriculum View original

  Is this image relevant?

• 

  Sensory Perception · Anatomy and Physiology View original

  Is this image relevant?

• 

  Hearing | Physics View original

  Is this image relevant?

• 

  Frequency, Wavelength, and Pitch ‹ OpenCurriculum View original

  Is this image relevant?

• 

  Sensory Perception · Anatomy and Physiology View original

  Is this image relevant?

1 of 3

Top images from around the web for Key terms in sound perception

• 

  Frequency, Wavelength, and Pitch ‹ OpenCurriculum View original

  Is this image relevant?

• 

  Sensory Perception · Anatomy and Physiology View original

  Is this image relevant?

• 

  Hearing | Physics View original

  Is this image relevant?

• 

  Frequency, Wavelength, and Pitch ‹ OpenCurriculum View original

  Is this image relevant?

• 

  Sensory Perception · Anatomy and Physiology View original

  Is this image relevant?

1 of 3

• Pitch
  • Perception of a sound's frequency
  • Higher frequency sounds perceived as higher pitch (flute, whistle)
  • Lower frequency sounds perceived as lower pitch (bass drum, tuba)
• Loudness
  • Perception of a sound's intensity or volume
  • Depends on both sound intensity and frequency
  • Louder sounds have higher intensity (jet engine vs whisper)
• Timbre
  • Characteristic quality distinguishing sounds of same pitch and loudness
  • Determined by specific mix of frequencies present (frequency spectrum)
  • Allows differentiation of instruments playing same note (guitar vs piano)
• Frequency
  • Number of wave cycles per second, measured in Hertz (Hz)
  • Human hearing range approximately 20 Hz to 20,000 Hz
  • Higher frequencies have shorter wavelengths (treble)
  • Lower frequencies have longer wavelengths (bass)

Effects of intensity and frequency

• Sound intensity
  • Measured in decibels (dB), a logarithmic scale
  • Each 10 dB increase represents tenfold increase in intensity
  • Higher intensity sounds generally perceived as louder (rock concert vs conversation)
• Frequency effects on loudness
  • Human ears most sensitive to frequencies between 2,000 and 5,000 Hz
  • Sounds in this range perceived louder than equal intensity at other frequencies
  • Equal-loudness contours (Fletcher-Munson curves) illustrate this relationship
• Loudness perception
  • Subjective measure of sound perception, influenced by intensity and frequency
  • Measured in phons, with 1 phon equal to 1 dB at 1,000 Hz
  • Doubling perceived loudness requires ~10 dB increase at most frequencies

Ear Structure and Function

Inner ear structure and function

• Outer ear
  • Pinna (visible part) and ear canal collect and direct sound waves (acoustic waves) toward middle ear
• Middle ear
  • Tympanic membrane (eardrum) and three small bones (ossicles): malleus, incus, stapes
  • Converts sound waves into mechanical vibrations and amplifies them
• Inner ear
  • Cochlea
    • Fluid-filled, snail-shaped structure contains basilar membrane and hair cells
  • Basilar membrane
    • Vibrates in response to mechanical vibrations from middle ear
    • Different frequencies cause maximum vibration at different locations (high frequencies at base, low at apex)
  • Hair cells
    • Attached to basilar membrane, bend in response to its vibration
    • Bending triggers neurotransmitter release, generating neural signals
  • Auditory nerve carries neural signals from hair cells to brain for processing and interpretation

Sound Localization and Processing

• Binaural hearing: Use of both ears to determine sound direction and distance
• Sound localization: Brain's ability to determine the origin of a sound in space
  • Relies on differences in timing and intensity between ears
• Auditory cortex: Region of the brain responsible for processing and interpreting auditory information
  • Analyzes complex sound features like pitch, timbre, and spatial location