17.6 Hearing
3 min read•june 18, 2024
Sound perception is a fascinating interplay of physics and biology. Our ears and brain work together to interpret sound waves, allowing us to distinguish , , and . 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 , 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
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- 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)
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- Perception of a sound's intensity or volume
- Depends on both sound intensity and frequency
- Louder sounds have higher intensity (jet engine vs whisper)
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- Characteristic quality distinguishing sounds of same pitch and loudness
- Determined by specific mix of frequencies present ()
- Allows differentiation of instruments playing same note (guitar vs piano)
- Frequency
- Number of wave cycles per second, measured in Hertz (Hz)
- Human 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 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
- (visible part) and ear canal collect and direct sound waves (acoustic waves) toward middle ear
- Middle ear
- (eardrum) and three small bones (): , ,
- Converts sound waves into mechanical vibrations and amplifies them
- Inner ear
- Cochlea
- Fluid-filled, snail-shaped structure contains and
- 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
- carries neural signals from hair cells to brain for processing and interpretation
- Cochlea
Sound Localization and Processing
- : Use of both ears to determine sound direction and distance
- : Brain's ability to determine the origin of a sound in space
- Relies on differences in timing and intensity between ears
- : Region of the brain responsible for processing and interpreting auditory information
- Analyzes complex sound features like pitch, timbre, and spatial location
Key Terms to Review (27)
Acoustic Wave: An acoustic wave is a mechanical disturbance that propagates through a medium, such as air, water, or a solid material, by the vibration of particles within that medium. These waves carry energy and can be used for various applications, including hearing, sonar, and ultrasound imaging.
Auditory Cortex: The auditory cortex is the part of the cerebral cortex that processes and interprets auditory information received from the ears. It plays a crucial role in our ability to perceive and understand sound, music, and speech.
Auditory Nerve: The auditory nerve, also known as the eighth cranial nerve, is a crucial component of the auditory system responsible for transmitting sound information from the inner ear to the brain. It plays a vital role in the process of hearing, enabling us to perceive and interpret the sounds around us.
Basilar Membrane: The basilar membrane is a key structural component of the inner ear, specifically within the cochlea. It plays a crucial role in the process of hearing by acting as a frequency analyzer, allowing the brain to perceive different sound frequencies.
Binaural Hearing: Binaural hearing is the ability to perceive sound using both ears, which allows the brain to locate the direction and distance of sound sources. This process is crucial for spatial awareness and understanding the auditory environment.
Cochlea: The cochlea is a spiral-shaped, fluid-filled structure located in the inner ear that plays a crucial role in the process of hearing. It is responsible for converting sound waves into electrical signals that can be interpreted by the brain.
Decibel: The decibel (dB) is a logarithmic unit used to measure the intensity or level of various quantities, including sound, electricity, and radio signals. It is a relative measure that compares the magnitude of a quantity to a reference value, often the threshold of human hearing or a standard power level.
Frequency Spectrum: The frequency spectrum refers to the range of all possible frequencies that can be observed or measured in a given context. It is a fundamental concept in the study of wave phenomena, including sound waves, electromagnetic waves, and other types of oscillations.
Hair Cells: Hair cells are sensory receptors found in the inner ear that are responsible for the transduction of sound vibrations into electrical signals, enabling the perception of hearing. These specialized cells play a crucial role in the auditory system by converting mechanical stimuli into neural impulses that are then interpreted by the brain.
Hearing: Hearing is the process by which sound waves are converted into electrical signals and interpreted by the brain. It involves the interaction of physical, physiological, and neurological processes.
Incus: The incus, also known as the anvil, is one of the three small bones in the middle ear that are responsible for transmitting sound vibrations from the eardrum to the inner ear. It is the second bone in the ossicular chain, connecting the malleus (hammer) to the stapes (stirrup).
Loudness: Loudness is the perception of the strength or intensity of a sound. It is influenced by both the amplitude of the sound wave and the sensitivity of the human ear.
Loudness: Loudness is a subjective perception of the intensity or volume of a sound. It is a measure of how strong or soft a sound appears to the human ear and brain, and it is influenced by various factors such as sound intensity and frequency.
Malleus: The malleus is one of the three small bones in the middle ear that transmit sound vibrations from the eardrum (tympanic membrane) to the inner ear. It is the largest and most lateral of the three ossicles (the other two being the incus and stapes).
Notes: Notes are sound waves with a specific frequency and pitch. They are fundamental in the study of acoustics and auditory perception.
Ossicles: The ossicles are a set of three small bones located in the middle ear that play a crucial role in the hearing process. These bones, known as the malleus, incus, and stapes, transmit sound vibrations from the eardrum to the inner ear, enabling the conversion of sound waves into electrical signals that can be interpreted by the brain.
Phon: A phon is a unit of perceived loudness level for pure tones. It is numerically equal to the sound pressure level in decibels (dB) of a 1 kHz tone that is perceived as equally loud.
Phon: A phon is a unit of perceived loudness, used to measure the subjective intensity of a sound as perceived by the human ear. It is closely related to the concept of sound pressure level, which is an objective measure of the physical intensity of a sound wave.
Pinna: The pinna is the visible, outer part of the ear that helps to funnel sound waves into the ear canal. It is the first part of the auditory system that plays a crucial role in the process of hearing.
Pitch: Pitch is the perceived frequency of a sound, determining how high or low it sounds. It is directly related to the frequency of the sound wave.
Pitch: Pitch is the perceived highness or lowness of a sound, determined by the frequency of the sound waves. It is a fundamental characteristic of sound that plays a crucial role in various aspects of acoustics, including sound perception, musical composition, and the Doppler effect.
Sound Localization: Sound localization is the ability of the auditory system to determine the location of a sound source in the environment. It involves the brain's processing of various cues, such as the differences in time and intensity of a sound reaching the two ears, to determine the direction and distance of the sound.
Stapes: The stapes is the smallest and innermost of the three ossicles (small bones) in the middle ear. It plays a crucial role in the transmission of sound vibrations from the tympanic membrane to the oval window, which leads to the inner ear.
Timbre: Timbre is the quality or color of a sound that distinguishes it from other sounds of the same pitch and volume. It is determined by the complex waveform produced by the source.
Timbre: Timbre, also known as tone color or quality, is the characteristic sound of a particular musical instrument or voice. It is the attribute of a sound that allows us to distinguish between different sound sources, even when they are playing the same pitch at the same volume.
Tympanic Membrane: The tympanic membrane, also known as the eardrum, is a thin, flexible tissue that separates the outer ear from the middle ear. It plays a crucial role in the process of hearing by transmitting sound vibrations from the external environment to the middle ear bones, allowing the conversion of sound waves into electrical signals that can be interpreted by the brain.
Ultrasound: Ultrasound is sound waves with frequencies above the upper limit of human hearing, typically above 20 kHz. It is used in medical imaging and industrial applications.