Chapter 7: Hearing Flashcards
amplitude
volume/intensity of a sound
frequency
number of wave cycles per second
how can amplitude be objectively measured?
in decibles
what is the perceptual dimension of amplitude?
loudness
how can frequency be objectively measured?
in hertz
what is the perceptual dimension of frequency?
pitch
what is the perceptual dimension of complexity?
timbre
what is timbre?
the perception/identity of the sound (ex. different voices, instruments, etc.)
what is a pure tone?
a single sine wave, which is not typically experienced in life as it has to be manufactured
what are complex tones?
many sine waves which we experience on a daily basis
what did Joseph Fourier do?
measured the individual components of complex tones to try to decipher them.
created the Fourier Analysis
what did Fourier discover?
sound waves follow natural laws; they are predictable.
what can you see using the Fourier analysis?
you can see the individual sine waves that make up the complex wave form.
The Fourier analysis can accurately determine the other waves because they are whole multiples of the fundamental frequency (first harmonic)
what allows for distinction of different sounds (specifically different instruments)?
the intensity of the harmonics (timbre)
Ossicles
smallest bones in the body
work as a set of gears to transmit sounds
tympanic membrane (eardrum)
vibrates in response to a sound wave
semicircular canals
involved in the vestibular system (balance)
cochlea (inner ear)
where the receptors are located and where sound waves are transformed into neural signals
eustachian tube
where the ears get plugged
what are the three ossicles called?
malleus, incus, stapes
what is the function of the malleus?
vibrates in response to the vibrations it receives from the tympanic membrane
what is the function of the stapes?
pounds against the cochlea
why is it important that the ossicles are made of bone?
the cochlea is filled with fluid, so force is needed in order to transmit a sound wave from air into a fluid
what is contained within the cochlea?
the basilar membrane
how is the basilar membrane tuned to different frequencies?
a narrow, thick base is tuned for high frequencies
a wide, thin apex is tuned for low frequencies
layers of inner hair cells vs outer hair cells
there are 3 layers of outer hair cells and only 1 layer of inner hair cells, and inner hair cells send the main signals to the brain, allowing you to hear
how do cilia function?
cilia move in response to movement of the basilar membrane and rub against the tectorial membrane to create an action potential in the hair cell
what is housed in the organ of corti?
the receptors for sound
how many outer hair cells are in the ear of a healthy person? how many inner hair cells?
12 thousand outer hair cells
3500 inner hair cells
what is the purpose of outer hair cells?
increases sensitivity to sound and helps amplify sound
what happens if the inner hair cells fail to function properly?
deafness
type I nerve fibres
thick, well myelinated fibres that receive signals from inner hair cells
type II nerve fibres
thin, not well myelinated fibres that receive signals from outer hair cells
what is the place code?
the actual place on the basilar membrane that responds to certain frequencies
temporal code (phase locking)
fires in synchronicity with sound
at what frequency does it become difficult to discriminate between sounds?
4000+ Hz
what do pitch neurons do?
respond to the structure of the sound and clean up the signal so that it can be perceived easily
conductive hearing problems
a result of problems conducting sound waves in the ear, usually from having water in the ear, a change in pressure, etc. Can be fixed
sensorineural hearing problems
results from neural signals not getting to the brain
what is the purpose of a cochlear implant?
re-establishes hearing, but not in a normal sense. allows for speech
how does a cochlear implant work?
micro-electrodes are implanted along the basilar membrane, allowing for generation of electrical signals that are sent down auditory nerve fibres
what type of sound is at the level of your ears?
azimuth
where is the location of sound sources processed?
in the brainstem
interaural time difference (ITD)
sound comes in one ear earlier than it does in the other ear (by micro-seconds), allowing the brain to locate where sound is coming from. most extreme when coming directly from one side of the head
interaural level difference (ILD)
head is blocking the sound so that the sound is less loud in the other ear. becomes less distinct the more directly in front the sound is. not applicable below 500Hz
what do spectral shape cues allow for?
allow you to detect whether a sound is coming from above or below
what do the folds and grooves of the pinna do?
affect how sound moves around in the auditory canal. makes a different sound signature when coming from above vs below
what is processed in the medial superior olives?
interaural time difference
what is processed in the lateral superior olives?
interaural level difference
what is the function of the inferior colliculus?
integrates information from the two olives
what does a lesion in the inferior colliculus result in?
an inability to locate where sound is coming from
where is Broca’s area located?
on the border of the temporal and frontal lobes
what is Broca’s area involved in?
speech production
what happens if there is damage to Broca’s area?
difficulty producing speech; very halting speech
where is Wernicke’s area located?
posterior temporal lobe
what is Wernicke’s area involved in?
language comprehension
what happens if there is damage to Wernicke’s area?
word salad: words spoken don’t make sense
what is the right hemisphere of the brain involved in when it comes to language?
prosody and processing rhythm, music, etc
what happens to language if there is damage to the right hemisphere?
can still comprehend and produce language, but may speak in a monotone
