Good Vibrations Flashcards
How are sounds created?
Sounds are created when when objects vibrate. The vibrations of an object (sound source) causes molecules in the object’s surrounding medium (air, water, or any other elastic medium that can transmit vibrations) to vibrate as well, causing pressure changes in the medium. These patterns of pressure changes are called sound waves.
Amplitude/intensity
the magnitude of the pressure change of a sound wave (the difference between the highest pressure and the lowest pressure of the wave). Measured in decibel. Amplitude is perceived as loudness: the more intense a sound wave, the louder it will sound.
Frequency
the number of times per second that a pattern of pressure change repeats. Measured in hertz (Hz). Frequency is perceived as pitch.
Pure tone
a pressure change pattern that can be described with a sine wave.
Fourier analysis
Any sound (even non-pure tones) can be described as a combination of sine waves by a procedure called Fourier analysis.
Harmonic spectrum
the spectrum of a complex sound in which each frequency component is at integer multiples of the lowest frequency
Fundamental frequency
the lowest frequency in a harmonic spectrum
Human hearing range
20 to 20000 Hz, 0 to 120 dB
Audibility threshold
the lowest sound pressure level that can be reliably detected across the frequency range of human hearing
Equal-loudness curves
a graph plotting sound intensity against the frequency for which a listener perceives constant loudness. Equal-amplitude sounds can be perceived as softer or louder than each other, depending on the frequencies of the sound waves.
Temporal integration
the perception of loudness depends on the summation of energy over a brief period of time. The reason why loudness depends on duration of exposure
Pitch
the perceptural quality that we describe as “high” or “low” - the property of the auditory system in terms of which sounds may be ordered on a musical scale extending from low to high.
Timbre
a psychological sensation by which a listener can judge that 2 sounds with the same loudness and pitch are different
Pinna
the funnel-like part of the ear that sticks out of the head. Sounds are first collected from the environment by the pinnae.
Ear canal
Sound waves are funneled by the pinna into and through the ear canal, which extends ~25 mm into the head. main purpose of the ear canal is to protect the tympanic membrane (eardrum), which is located at its inner end, from damage.
ossicles
the middle ear consists of 3 tiny bones - the ossicles, which amplify sound waves: malleus, incus, stapes
tympanic membrane
a thin sheet of skin that moves in/out in response to the pressure changes of sound waves. also the border between the outer ear and the middle ear.
malleus (hammer)
connected to the tympanic membrane on one side and to the second ossicle
incus (anvil)
connected to the malleus and to the third ossicle
stapes (stirrup)
the third ossicle which transmits the vibrations of sound waves to the oval window
oval window
membrane that forms the border between the middle ear and the inner ear. pressure on the oval window is magnified 18 times relative to the pressure on the tympanic membrane. this amplification is important for our ability to hear faint sounds, because the inner ear is made up of a collection of fluid-filled chambers (and liquid takes more energy to move than air).
middle-ear muscles
2 muscles, attached to the ossicles, that perform the acoustic reflex, which protects the ear from intense sounds
tensor tympani
attached to the malleus. their main role is to tense when sounds are very loud. this way they restrict movement of the ossicles and thus suppress pressure changes that might be large enough to damage the delicate structures in the inner ear.
stapedius
attached to the stapes. their main role is to tense when sounds are very loud. this way they restrict movement of the ossicles and thus suppress pressure changes that might be large enough to damage the delicate structures in the inner ear.
cochlea
a snaillike structure (main structure of the inner ear)
scola vestibuli
a channel in the upper half of the uncoiled cochlea
scala tympani
a channel in lower half of the uncoiled cochlea
cochlear partition
separates scala vestibuli and scala tympani. it extends from the base of the cochlea (near the stapes) until its apex at the far end. it contains structurs that transform the vibrations inside the cochlea into electricity.
organ of corti
a structure in the cochlear partition, which contains hair cells - the receptors for hearing. The human ear contains 1 row of inner hair cells and 3 rows of outer hair cells.
basilar membrane
the structure on which the organ of Corti is located
stereocilia
small processes at the tips of hair cells, which bend in response to pressure changes. the stereocilia of the tallest row of outer hair cells are embedded in the tectorial membrane - a structure attached to the organ of Corti. The other stereocilia are not.
oval window
the back & forth motion of the oval window transmits vibrations to the liquid inside the cochlea, which sets the basilar membrane into motion. this results in:
1. The organ of Corti being set into an up-and-down vibration
2. The tectorial membrane moving back and forth
auditory nerve
a collection of neurons that convey information from hair cells in the cochlea to the brain stem and back
place code
different places on the cochlea are tuned to different sound frequencies. higher frequencies cause the largest displacements closer to the oval window, near the base of the cochlea. lower frequencies cause the largest displacements farther away, closer to the apex
tonotopic map
the map of the cochlea that shows which part vibrate the most in response to which frequencies
cochlear amplifier
a mechanism through which the cochlea can actively sharpen its tuning to a specific frequency. Most of the auditory nerve fibers that synapse with the outer hair cells are efferent. They play a role in determining what kind of information is sent on to the brain by the afferent fibers
neural frequency tuning curve (NTFC)
a curve that represents the sensitivity of a neuron to different sound frequencies. It is constructed by presenting tones of different frequencies and measuring the sound level necessary to cause the neuron to increase its firing rate.
characteristic frequency
the frequency to which the neuron is most sensitive (has the lowest sound level threshold)
two-tone suppression
when a second tone of a slightly different frequency is added, the rate of firing of an auditory nerve fiber in response to a first tone is decreased
rate saturation
the point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate
rate-intensity function
a function representing the firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities
low-spontaneous fiber
an AN fiber that has a low rate (<10 spike/s) of spontaneous firing. They require higher intensity to start firing, but retain their selectivity over a broader range of intensities
high-spontaneous fiber
an AN fiber that has a high rate (>30 spike/s) of sponaneous firing. they are very sensitive to low levels of sound, but quickly reach saturation
mid-spontaneous fiber
an AN fiber that has a medium rate (10-30 spike/s) of spontaneous firing
phase locking
auditory nerve fibers fire at one distinct point the cycle of a sound wave at a given frequency. This results from the alternating bursts of electrical signals at the stereocilia, which are synchronized with the pressure changes
temporal coding
the firing pattern of an AN fiber carries a code for the sound wave frequency (e.g. an AN fiber firing an action potential 100 times per second means that it is responding to a sound wave that includes a frequency component of 100 Hz)
Volley principle
a hypothesis that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire on every period
Cranial nerve VII (vestibulocochlear nerve)
carries the auditory nerve and the nerve fibers of the vestibular system
cochlear nucleus
AN fibers synapse in the cochlear nucleus in the brain stem, which contains many specialized neurons, for example: neurons sensitive to onsets of sounds of particular frequencies; neurons sensitive to the coincidence of onsets across many frequencies
superior olive
some of the neurons from the cochlear nucleus project to the superior olive (another brain stem nucleus). here signals from the left and right ears first meet, which makes the superior olive important for localizing sounds
inferior colliculus
neurons from the cochlear nucleus and superior olive project to the inferior colliculus. most of the input to each inferior colliculus comes from the contralateral ear
medial geniculate nucleus (MGN)
a thalamic nucleus to which the auditory pathway continues from the inferior colliculi. Just like the LGN, the MGN has many more input connections (efferent) from the cortex than output connections (afferent) to the cortex
tonotopic organization
all structures of the auditory system show organization based on frequency
primary auditory cortex (A1)
the auditory pathway continues here after the MGN
belt area
neurons in A1 project to the surrounding belt area of the cortex
parabelt area
neurons from the belt project to neurons in the adjacent parabelt area
anterior auditory cortex
contains area most responsive to pitch
conductive hearing loss
occurs when the ossicles lose (or are impaired in) their ability to freely convey vibrations from the tympanic membrane to the oval window
otosclerosis
a type of conductive hearing loss caused by abnormal growth of the ossicles
sensorineural hearing loss
the most common and serious form of hearing loss caused by defects in the cochlea or auditory nerve
metabolic losses
caused by changes in the fluid environment of the cochlea that decrease the activity of hair cells
sensory losses
caused by injury to hair cells due to drugs or excessive exposure to noise
presbycusis
a sensorineural hearing loss caused by hair cell damage resulting from noise exposure, hair-cell-damaging drugs and age-related degeneration
hidden hearing loss
some people might have normal sensitivity to low-intensity sounds but have damaged auditory nerve fibers, as indicated by being unable to hear speech in noisy environments
cochlear implants/prosthetics
electronic cochlear-like implants with electrodes along their length, used for providing basic hearing to deaf people
