Hearing: Physiology and Psychoacoustics

Flashcards covering the physiology of hearing, psychoacoustics, and types of hearing loss based on the lecture notes.

Function of Hearing

Helps you stay aware of your surroundings and identify & recognize objects based on the sounds they produce.

Sound

Created when objects vibrate, causing molecules in the surrounding medium to vibrate and creating pressure changes.

Amplitude or Intensity

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

Loudness

The psychological aspect of sound related to perceived intensity (amplitude).

Frequency

For sound, the number of times per second that a pattern of pressure change repeats, perceived as pitch.

Pitch

The psychological aspect of sound related mainly to the perceived frequency. Low frequencies correspond to low pitches, high frequencies to high pitches.

Timbre

The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar.

Decibels (dB)

Unit of measure for the physical intensity of sound (sound pressure level).

Hertz (Hz)

Unit of measure for frequency, where 1 Hz equals 1 cycle per second. Humans hear from 20-20,000 Hz.

Sine Wave (Pure Tone)

A simple sound waveform for which variation as a function of time is a sine function, not common in everyday sounds.

Fourier Analysis

A mathematical technique that decomposes a complex function into simpler, constituent sine and cosine waves.

Harmonic Spectrum

The spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency.

Fundamental Frequency

The lowest-frequency component of a complex periodic sound, typically caused by a simple vibrating source.

Spectrogram

A pattern for sound analysis that provides a three-dimensional display, plotting time on the horizontal axis, frequency on the vertical axis, and intensity in color or gray scale.

Outer Ear

Consists of the pinna and ear canal, which collect sounds and funnel them to the eardrum, enhancing certain frequencies.

Tympanic Membrane (Eardrum)

Vibrates in response to sound, moving the malleus; the border between the outer and middle ear.

Ossicles

Three tiny bones (malleus, incus, stapes) in the middle ear that amplify sound waves and transfer their energy to the cochlea via the oval window.

Acoustic Reflex

Muscles that tense when sounds are loud, muffling pressure changes to protect the inner ear.

Inner Ear

The region where fine changes in sound pressure are transduced into neural signals.

Cochlea

A spiral structure of the inner ear containing the organ of Corti, filled with watery fluids in three parallel canals.

Vestibular Canal (Scala Vestibuli)

The canal closest to ossicles, extending from the oval window to the helicotrema, through which pressure waves move first.

Tympanic Canal (Scala Tympani)

Extends from the helicotrema to the round window at the base of the cochlea.

Middle Canal (Scala Media)

Sandwiched between the vestibular and tympanic canals, containing the cochlear partition and endolymph.

Basilar Membrane

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

Organ of Corti

A structure on the basilar membrane of the cochlea, composed of hair cells and dendrites of auditory nerve fibers, where mechanical movements are translated into neural signals.

Hair Cells

Cells in the organ of Corti that support the stereocilia, which transduce mechanical movement in the cochlea into neural activity.

Stereocilia

Tips of hair cells that, when flexed, initiate the release of neurotransmitters.

Tectorial Membrane

A gelatinous flap connected at one end that rests on top of hair cells, interacting with stereocilia during sound transmission.

Inner Hair Cells

Convey almost all information about sound waves to the brain (using afferent fibers).

Outer Hair Cells

Receive information from the brain (using efferent fibers) and are involved in a feedback system that influences inner hair cell sensitivity and tuning.

Auditory Transduction

The process by which changes in sound pressure are translated into neural signals, occurring in the inner ear, specifically the organ of Corti.

Place Coding

Responses of individual auditory nerve (AN) fibers to different frequencies are related to their place along the basilar membrane of the cochlear partition.

Characteristic Frequency (CF)

The frequency to which a particular auditory nerve fiber is most sensitive; its response is clearest when sounds are faint.

Two-Tone Suppression

A decrease in the response (firing rate) of one auditory nerve fiber to one tone when a second tone is presented at the same time, especially if the second tone is lower in Hz.

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.

Temporal Code for Sound Frequency

Information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of the sound.

Phase Locking

Firing of a single neuron at one distinct point in the period (cycle) of a sound wave at a given frequency.

Volley Principle

An idea stating 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.

Tonotopic Organization

An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency, maintained from the cochlea through primary auditory cortex (A1).

Cochlear Nucleus

The first brainstem nucleus where afferent auditory nerve fibers synapse.

Superior Olive

A brainstem nucleus where inputs from both ears can converge early in the auditory pathway.

Inferior Colliculus

A midbrain nucleus in the auditory pathway.

Medial Geniculate Nucleus

Part of the thalamus that relays auditory signals and receives input from the auditory cortex.

Primary Auditory Cortex (A1)

The first area within the temporal lobes that processes acoustic information.

Psychoacoustics

Branch of psychophysics that studies the psychological correlates of the physical dimensions of acoustics to understand how the auditory system operates.

Audibility Threshold

The lowest sound pressure level that can be reliably detected at a given frequency.

Equal-Loudness Curve

A graph plotting sound pressure level against frequency for which a listener perceives constant loudness.

Temporal Integration

The process by which a sound at a constant level is perceived as being louder when it is of greater duration (occurs over 100 to ~200ms).

Masking

Using a second sound, frequently noise, to make the detection of another sound more difficult.

White Noise

Noise consisting of all audible frequencies in equal amounts.

Critical Bandwidth

The range of frequencies conveyed within a channel in the auditory system, beyond which a target sound is no longer perceivable amidst noise.

Conductive Hearing Loss

Hearing loss caused by problems with the bones of the middle ear, such as otosclerosis (abnormal growth of middle ear bones).

Sensorineural Hearing Loss

The most common and serious auditory impairment, due to defects in the cochlea or auditory nerve, often from damaged hair cells or metabolic issues.

Temporary Threshold Shift

Swelling of hair cells, resulting in muffled sounds, which can be temporary unless exposure to loud noises is repeated.

Tinnitus

A 'ringing in your ears' sensation, often caused by extended exposure to loud sounds.

Hidden Hearing Loss

Damage to hearing from a loss of synapses between auditory nerve fibers and hair cells, resulting in less connectivity for information transfer in the auditory cortex, despite intact sensation.

Presbycusis

Age-related hearing loss.

Cochlear Implant

A device with miniature electrodes threaded through the cochlea, used to restore hearing in sensorineural hearing loss by directly activating electrodes at appropriate positions along the implant.