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Describe the two basic qualities of sound: frequency and amplitude.

-Frequency (for sound) is the number of times per second that a pattern of pressure change repeats. Frequency is perceived as pitch.
-Amplitude (or intensity) The magnitude of displacement (increase or decrease) of a sound pressure wave.


How is amplitude associated with loudness?

Amplitude is perceived as loudness.


What is a sine wave and why is it important in studying auditory perception?

A sine wave is a waveform for which variation as function of time is a sine function. It is important to studying auditory perception because it is a pure tone, and the shape of sound waves.


Describe the concept of timbre

Timbre is the psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies


How is Sound Created

Sound is created by motions and vibrations of objects in the environment. The nature of these motions is determined by forces impinging on the objects and their resonance characteristics.


What are the roles of the ear canal?

The ear canal's length and shape enhance sound frequencies between about 2000 and 6000 HZ, but the main purpose is to protect the tympanic membrane.


Describe the three tiny bones in the middle ear.

The three tiny bones in the ear (or the ossicles) are the malleus, incus and stapes. The malleus receives vibrations from the tympanic membrane and is attached to the incus. The incus connects the malleus to the stapes. The stapes presses against the oval window of the cochlea.

The ossicles amplify sound in two ways. 1.) their joints are hinged in such a way that the work like levers: a modest amount of energy becomes larger on the other. This lever action increases the amount of pressure change by about a third. 2.)They also increase the energy transmitted to the inner ear by concentrating energy fro a larger to a smaller surface area: the tympanic membrane, which moves the malleus about 18 times as large as the oval window, moved by the stapes.


Why can't the acoustic reflex help protect the ear from abrupt loud sounds, such as gun fire?

The acoustic reflex (controlled by the tensor tympani and the stapedius) follows the onset of loud sounds by 1/5 of a second. It is not fast enough to muffle sounds as fast as a gun firing.


What is the function of the cochlea?

The cochlea translates the information carried by sound waves into neural signals. The tiny coiled structure allows vibrations pushed and pulled through the oval window to create waves o pressure changes to flow through the fluid of the vestibular canal. The displacement travels from the base of the cochlea, to its apex, to be interpreted by the organ of Corti.


Describe how the release of neurotransmitters results from the deflection of stereocilia.

Deflection of a hair cell's stereocilia causes a change in voltage potential that initiate the release of neurotransmitters, which in turn encourages firing by auditory nerve fibers that have dendritic synapes on hair cells.

When a sterocilium deflects the tip link pulls on a larger stereocilium in a way that opens an ion pore somewhat like opening a small gate for a short period of time. This action permits K+ ions to flow rapidly into the hair cell, causing rapid depolarization. This depolarization leads to a rapid influx of Ca2+ (calcium ions) and initiation of the release of neurotransmitters from the base of the hair cell to stimulate dendrite of the auditory nerve.


How is place code related to tuning?

Different parts of the cochlea relate to different frequencies in the cochlea. This tuning is known as “place code” for sound frequency. It is caused by the way the structure of the basilar membrane changes along the length of the cochlea. The cochlea as a whole narrows from base to apex, but the basilar membrane actually widens toward the apex. In addition, the basilar membrane is thick at the base and becomes thinner as it widens. As a result, the cochlea separates frequencies along its length like an acoustic prism. Higher frequencies bend the narrower, stiffer regions of the basilar membrane more, and the lower frequencies cause greater displacements in the wider, more flexible regions near the apex.


How are inner hair cells different from outer hair cells?

Over 90% of the afferent fibers in the auditory nerve-- fibers that information to the brain--synapse on the 3500 inner hair cells (10-30 auditory nerve fibers listen to one inner hair cell).
The outer hair cells serve a more mechanical role. Most of the nerve fibers that synapse with the outer hair celss are efferent fibers, conveying information FROM the brain. When these efferent fibers become active, outer hair cells that are connected to these fibers become longer and this makes the nearby cochlear partition stiffer that other parts, making the cochlea more sensitive and more sharply tuned to particular frequency.


What is the threshold tuning curve?

The threshold tuning curve is a graph plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response.


What happens during two-tone suppression?

There is a decrease in the firing rate of one auditory nerve fiber due to one tone, when a second tone is presented at the same time.The suppression effect appears to be caused by mechanical changes to the basilar membrane.


What does an isointensity curve show us?

An isointensity curve is a map plotting the firing rate of an auditory nerve fiber against varying frequencies at a steady intensity.


What is rate saturation?

Rate saturation is the point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate.


Why does phase locking occur?

Phase locking (firing of a single neuron at one distinct point in the cycle of a sound wave at a given frequency) may occur because AN fibers fire when the sterocilia of hair cells move in one directions but do not fire when the sterocilia move in the other direction. This carries a temporal code for the sound wave frequency.


Describe the volley principle.

The volley principle is the idea that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in a period of a sound wave, but does not fire fire on every period. Multiple AN fibers together can provide a temporal for frequency if different neurons each fire at different period of the sine wave.


What kind of organization exists in the primary auditory cortex (A1)?

Tonotopic organization. Neurons from A1 project to the surrounding belt area of cortex, and neurons from this belt synapse with neurons in the adjacent parabelt area. Just about any sound will cause activation in some part of A1. Processing proceeds from simpler to more complex stimuli as we move farther along the auditory pathway.


What is psychoacoustics?

Psychoacoustics is the study of the psychological correlates of the physical dimensions of acoustics; a branch of psychophysics.


What is the audibility threshold?

the audibility threshold is the lowest sound pressure level that can be reliably detected at a given frequency


What is white noise and when is it used?

White noise is noise consisting of all audible frequencies in equal amounts. White noise in hearing is analogous to white light in vision, for which all wave lengths are present.


Describe two kinds of hearing loss.

Otitis media-inflammation of the middle ear, commonly in children as a result of infection
Otosclerosis-Abnormal growth of the middle-ear bones that causes hearing loss.


acoustic reflex

A reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles.


afferent fiber

A neuron that carries sensory information to the central nervous system.


amplitude or intensity

The magnitude of displacement (increase or decrease) of a sound pressure wave. Amplitude is perceived as loudness.


auditory nerve fiber

A collection of neurons that convey information from hair cells in the cochlea to (afferent) and from (efferent) the brain stem.


basilar membrane

A plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea.


belt area

A region of cortex, directly adjacent to the primary auditory cortex (A1), with inputs from A1, where neurons respond to more complex characteristics of sounds.


characteristic frequency (CF)

The frequency to which a particular auditory nerve fiber is most sensitive.