Auditory System Flashcards
What are sound waves in simple terms?
Air molecules that undergo displacement and compression by changing pressure
What are three physical attributes of sound waves?
Frequency, amplitude and complexity
What is frequency and pitch perception?
The rate at which sound waves vibrate, measured as cycles per second or hertz.
What is amplitude and perception of loudness (how is it measured)?
Intensity of sound measured in decibles (dB).
What is complexity and timbre (perception of sound quality) and their relation to each other?
A sound’s complexity is a mixture of frequencies. Complexity determines timbre.
What is this sound wave?
Low frequency (low-pitch)
What is this sound wave?
High frequency (high-pitch)
What is this sound wave?
High amplitude (loud sound)
What is this sound wave?
Low amplitude (soft sound)
What is this sound wave?
Simple (pure tone)
What is this sound wave?
Complex (mix of frequencies)
How are differences in frequency heard?
Differences in pitch (think piano)
What is the lowest frequency a healthy adult human can hear?
20Hz
What is the highest frequency a healthy adult human can hear?
20000Hz
What is true about animals and their communication in relation to frequency?
Many animals communicate with sound, with species-specific sounds that their auditory systems have evolved to hear.
True or false: Very low frequencies tend to travel well in water.
True
True or false: High frequency sounds can act like sonar.
True
What is the term for the intensity of a sound, measured in dB?
Amplitude.
What sound wave corresponds with our perception of loudness?
Amplitude
If you hit a tuning fork lightly, it resonates at a certain frequency (tone). If you hit the same fork harder, it produces the same tone, but you transfer more energy into the vibrations. This is an example of what?
Amplitude
What is the amplitude of typical speech sounds?
40dB
What is true about sound perception of frequency and amplitude together?
You can perceive more than one sound at a time because each sound wave’s frequency stimulates different neurons in our auditory system.
Give an example of low frequency, low amplitude.
Low pitch and soft volume (faucet dripping)
Give an example of low frequency, high amplitude.
Low pitch and loud volume (lawnmower)
Give an example of high frequency, low amplitude.
High pitch and soft volume (bird whistle)
Give an example of high frequency, high amplitude.
High pitch and high volume (fire alarm)
What are pure tones?
Sounds with a single frequency
What are complex tones?
Sounds with a mixture of frequencies and amplitudes combined and overlayed
How do sound waves allow humans to distinguish between voices?
Different timbre, or “uniqueness”
Where are auditory stimuli routed in the brain?
Routed through the brainstem (various structures) then on to the auditory cortex (A1)
What is the auditory system designed to do?
Decode frequency, amplitude, and complexity to analyze sounds for meaning and location
What is true about the evolution of sound-processing capabilities in humans over time?
Associated with the expansion of the temporal lobes.
What are 3 main regions of the human ear?
Outer ear, middle ear, inner ear.
What is the main purpose of the outer ear?
Processing sound waves
What are the 3 main structures of the outer ear?
Pinna, external ear canal, eardrum
What is the Pinna and its function in hearing?
A funnel-like external structure that catches sound waves in the surrounding environment and deflects them into the ear canal
What is the external ear canal and its function in hearing?
Responsible for narrowing and amplifying sound waves, and directing them to the tympanic membrane (eardrum)
What is the tympanic membrane?
The eardrum
What is the eardrum and its role in hearing?
Structure that vibrates in response to sound waves.
What is found to the inner side of the eardrum?
The middle ear
What is the middle ear?
An air filled chamber that contains ossicles
What are ossicles?
The three smallest bones in our bodies that attach the eardrum to the oval window.
What are the 3 ossicles?
Hammer, Anvil, Stirrup (also referred to as Malleus, Incus, Stapes)
What is the oval window?
An opening in the casing of the cochlea
How does the inner ear process sound waves after vibrating the eardrum?
When sound waves vibrate the eardrum, the vibrations are transmitted to the ossicles who then amplify them and convey them through the oval window to the cochlea.
What is the cochlea?
Coiled structure in the inner ear; filled with cochlear fluid and auditory receptor cells
What is the organ of Corti?
Auditory cells & the cells that support the auditory receptor cells
What are the 3 composing elements of the organ of Corti?
Basilar membrane, Outer and inner hair cells, Tectorial membrane
What is the basilar membrane?
Receptor surface in the cochlea; converts sound waves to neural activity
What are the outer and inner ear hair cells?
Sensory neurons in the cochlea that are tipped by cilia. They are embedded in the basilar and tectorial membranes
What is the Tectorial membrane?
Membrane overlying hair cells
How does the inner ear process sound waves after passing through the cochlear fluid?
The waves travelling through the fluid bend the basilar and tectorial membranes which stimulates the cilia at the tips of the hair cells.
What does this image show?
A cross-section of the cochlea and the organ of Corti
How does the ear work to convert sound saves into neural impulses?
Frequencies cause all parts of the basilar membrane to bend
What did Helmholtz suggest about sound waves and the basilar membrane?
Sound waves of different frequencies cause different parts of the basilar membrane to bend
How was Helmholtz wrong about the way the basilar membrane bends?
All frequencies cause all parts of the basilar membrane to bend
What did Békésy suggest about the responsiveness of the basilar membrane to frequencies of sound?
High frequencies = maximum displacement at the base.
Low frequencies= maximum displacement at the apex.
What is the maximal Hz sensitivity of the base of the basilar membrane?
20000 Hz
What is the maximal Hz sensitivity of the apex of the basilar membrane?
100 Hz
How does the basilar membrane vary in thickness along its length?
Narrow and thick at its base
Wide and thin at its apex
How do differences in thickness of the basilar membrane help code sound?
Differences in dimension help code for very small differences in frequency.
What is the pathway to the auditory cortex?
Cochlear nucleus –> olivary complex –> trapezoid body –> inferior colliculus –> medial geniculate nucleus –> auditory cortex
What are the two pathways of auditory stimuli?
Ventral and dorsal
Ventral pathway projects to the primary auditory cortex (A1)
Dorsal region projects to the auditory regions adjacent to A1.
What is the role of the the ventral auditory pathway?
“What” pathway –> where is that noise coming from
Where is the primary auditory cortex (A1)?
The primary auditory cortex, A1, lies within Heschl’s gyrus, surrounded by secondary cortical areas, A2.
What is the role of Wernicke’s area?
Speech comprehension and analysis –> left hemisphere dominance
What is the role of Heschl’s gyrus?
Analyzing music
What is the role of the insular lobe?
Related to language, taste perception and social cognition.
What is Tonotopic representation?
Structural organization for processing sound waves from lower (apex) to higher (base) frequencies –> reproduced in the cochlear nucleus and is maintained throughout the auditory pathways and into A1.
How do cochlear implants work?
Implanted surgically in the inner ear to convert sound waves to neural activity –> redirects sound to proper place on the basilar membrane ** only works to replace structures BEFORE the basilar membrane
What are the two mechanisms for locating sound?
Interaural time difference (ITD) and Interaural intensity diffrerence (IID)
Explain how Interaural time differences are processed
Neurons compute differences in arrival time in each ear, carried out in the olivary complex
Explain how Interaural intensity differences are processed
Neurons in the brainstem compute the difference in a sound wave’s relative loudness on the left and right side –> detected by lateral part of olivary complex and trapezoid body
How do owls detect sound from location?
ITD
True or false: Language functions are partly localized
True
What is the anterior speech area in the frontal lobe that functions with the motor cortex to produce the movements needed for speaking?
Broca’s area
What is the posterior speech area at the rear of the temporal lobe that regulates language comprehension?
Wernicke’s area
90-95% of aphasia cases are the result of damage to which cerebral hemisphere?
Left cerebral hemisphere
What is aphasia?
Disturbed language processing caused by brain dysfunction
What is nonfluent aphasia (Broca’s aphasia, expressive aphasia)?
A person continues to comprehend speech but has to labor to produce it – short, hesitant phrases with errors and omission of function words
What is fluent aphasia (Wernicke’s aphasia, receptive aphasia)?
Impairments in language reception– severe disturbance in comprehension… Word production is intact.
What causes fluent aphasia?
Damage to the posterior temporal/parietal regions
What is the arcuate fasciculus?
Area of connection between Broca’s and Wernicke’s areas/.
Where is music processing?
Right hemisphere with some left hemisphere influence (music production).
