Key Questions
How can sound be described physically and perceptually?
What factors contribute to the timbre of a sound?
What does the equal loudness curve represent?
What are the structures and functions of the outer, middle, and inner ears?
What are the receptors for audition, and how does transduction occur?
What are the pathways for audition?
How do different theories explain pitch perception?
What are the symptoms and treatments for tinnitus? How can hearing loss be prevented?
Sound: Waves in the air produced by a vibrating object, detected by the auditory system.
Distal stimulus: The vibrating object.
Proximal stimulus: Pattern of energy at the eardrum.
Phase: Point along the wave, measured in degrees (no direct perceptual counterpart).
Amplitude: Displacement of wave from peak to trough.
Range of audible amplitudes: threshold = 0.0002 dynes/cm², maximum = 200 dynes/cm²; difference of 1000×.
Decibels (dB) used for large amplitude ranges: dB = 20 log (p /p0) where p = sound pressure level, p0 = threshold SPL (20 µPa).
Frequency: Number of sound wave cycles per second; measured in Hertz (Hz).
Formula: Hz = # of cycles/time (s).
Loudness: Perceptual experience of sound intensity (not "volume"). Associated with amplitude & sound pressure.
To measure: compare to a standard sound (1000 Hz pure tone at 40 dB = 1 sone of loudness).
Doubling loudness: increase dB by ~10 dB (e.g., 60 dB is twice as loud as 50 dB).
Pitch: Quality of a sound; allows sounds to be ordered on a musical scale.
Range: 20 - 20,000 Hz.
Affected by intensity:
High-frequency sounds seem higher pitched as intensity increases.
Low-frequency sounds seem lower pitched as intensity increases.
Duration effects: sound < 10 ms long is heard as a “click.”
Sound waves: pressure variations in air due to surface vibration.
Waves may cause compression (high pressure) and rarefaction (low pressure).
Cycle: Time between two consecutive high peaks.
Sound energy weakens across time and space.
Speed of sound varies; e.g., travels faster in water vs. air.
Pure tones: Sound waves where pressure changes follow a sine wave format; most sounds are complex waves.
Waveform: Represents different frequencies heard at a particular pitch.
High amplitude = loud (high intensity).
Chromatic Scale: One note is an octave above another when its frequency is double. Subdivided into 12 intervals equally spaced logarithmically.
Fourier Analysis: Analyzes musical notes; lowest frequency in spectrum is fundamental.
Harmonics: Frequencies that are integer multiples of the fundamental.
Timbre: Character of sound; differences in sound quality for different instruments playing the same note.
Each frequency has a different threshold.
Equal Loudness Curve: Describes absolute threshold for hearing different frequencies; auditory response area ranges from threshold to pain.
Phase Cancellation: Sound waves out of phase can cancel each other out (e.g., noise-canceling headphones).
Pinna: External “ear” channels sound waves into the external auditory meatus, amplifying frequencies between 2000 to 5000 Hz.
Tympanic Membrane (Eardrum): Vibrates in response to sound waves, transmits sound to middle ear structures.
Ossicles: Malleus, incus, stapes (amplify sound).
Concentrate vibrations from the larger eardrum to the oval window.
Eustachian Tube: Equalizes pressure between middle ear and environmental pressure.
Cochlea: Coiled structure with three fluid-filled chambers; responsible for sound transduction.
Hair Cells: Located in the Organ of Corti; transduce mechanical vibrations into neural signals.
Transduction Steps: Vibration of eardrum causes movement through ossicles to the oval window and cochlear partition, creating shear forces that bend hair cell cilia.
Auditory Pathways: Axons of spiral ganglion converge to form auditory nerve; superior olives send feedback to outer hair cells.
Place Code: Specific neurons encode different frequencies; activated hair cells indicate perceived pitches.
Frequency Theory: Entire basilar membrane vibrates synchronously with sound frequency.
Volleys: Neurons fire alternately to encode higher frequencies.
Definition: Ringing sound in ears without external stimulus affecting 13 million North Americans.
Commonly caused by loud sounds, certain drugs, and ear infections.
Treatments: No cure, but therapies like tinnitus maskers may help.
Noise-Induced Hearing Loss (NIHL): Significant increase in auditory disorders; chronic exposure leads to irreversible damage.
Prevention: Limit exposure to loud noises, use hearing protection, be aware of occupational risks.
Ch 10
Key Questions
How can sound be described physically and perceptually?
What factors contribute to the timbre of a sound?
What does the equal loudness curve represent?
What are the structures and functions of the outer, middle, and inner ears?
What are the receptors for audition, and how does transduction occur?
What are the pathways for audition?
How do different theories explain pitch perception?
What are the symptoms and treatments for tinnitus? How can hearing loss be prevented?
Sound: Waves in the air produced by a vibrating object, detected by the auditory system.
Distal stimulus: The vibrating object.
Proximal stimulus: Pattern of energy at the eardrum.
Phase: Point along the wave, measured in degrees (no direct perceptual counterpart).
Amplitude: Displacement of wave from peak to trough.
Range of audible amplitudes: threshold = 0.0002 dynes/cm², maximum = 200 dynes/cm²; difference of 1000×.
Decibels (dB) used for large amplitude ranges: dB = 20 log (p /p0) where p = sound pressure level, p0 = threshold SPL (20 µPa).
Frequency: Number of sound wave cycles per second; measured in Hertz (Hz).
Formula: Hz = # of cycles/time (s).
Loudness: Perceptual experience of sound intensity (not "volume"). Associated with amplitude & sound pressure.
To measure: compare to a standard sound (1000 Hz pure tone at 40 dB = 1 sone of loudness).
Doubling loudness: increase dB by ~10 dB (e.g., 60 dB is twice as loud as 50 dB).
Pitch: Quality of a sound; allows sounds to be ordered on a musical scale.
Range: 20 - 20,000 Hz.
Affected by intensity:
High-frequency sounds seem higher pitched as intensity increases.
Low-frequency sounds seem lower pitched as intensity increases.
Duration effects: sound < 10 ms long is heard as a “click.”
Sound waves: pressure variations in air due to surface vibration.
Waves may cause compression (high pressure) and rarefaction (low pressure).
Cycle: Time between two consecutive high peaks.
Sound energy weakens across time and space.
Speed of sound varies; e.g., travels faster in water vs. air.
Pure tones: Sound waves where pressure changes follow a sine wave format; most sounds are complex waves.
Waveform: Represents different frequencies heard at a particular pitch.
High amplitude = loud (high intensity).
Chromatic Scale: One note is an octave above another when its frequency is double. Subdivided into 12 intervals equally spaced logarithmically.
Fourier Analysis: Analyzes musical notes; lowest frequency in spectrum is fundamental.
Harmonics: Frequencies that are integer multiples of the fundamental.
Timbre: Character of sound; differences in sound quality for different instruments playing the same note.
Each frequency has a different threshold.
Equal Loudness Curve: Describes absolute threshold for hearing different frequencies; auditory response area ranges from threshold to pain.
Phase Cancellation: Sound waves out of phase can cancel each other out (e.g., noise-canceling headphones).
Pinna: External “ear” channels sound waves into the external auditory meatus, amplifying frequencies between 2000 to 5000 Hz.
Tympanic Membrane (Eardrum): Vibrates in response to sound waves, transmits sound to middle ear structures.
Ossicles: Malleus, incus, stapes (amplify sound).
Concentrate vibrations from the larger eardrum to the oval window.
Eustachian Tube: Equalizes pressure between middle ear and environmental pressure.
Cochlea: Coiled structure with three fluid-filled chambers; responsible for sound transduction.
Hair Cells: Located in the Organ of Corti; transduce mechanical vibrations into neural signals.
Transduction Steps: Vibration of eardrum causes movement through ossicles to the oval window and cochlear partition, creating shear forces that bend hair cell cilia.
Auditory Pathways: Axons of spiral ganglion converge to form auditory nerve; superior olives send feedback to outer hair cells.
Place Code: Specific neurons encode different frequencies; activated hair cells indicate perceived pitches.
Frequency Theory: Entire basilar membrane vibrates synchronously with sound frequency.
Volleys: Neurons fire alternately to encode higher frequencies.
Definition: Ringing sound in ears without external stimulus affecting 13 million North Americans.
Commonly caused by loud sounds, certain drugs, and ear infections.
Treatments: No cure, but therapies like tinnitus maskers may help.
Noise-Induced Hearing Loss (NIHL): Significant increase in auditory disorders; chronic exposure leads to irreversible damage.
Prevention: Limit exposure to loud noises, use hearing protection, be aware of occupational risks.