Auditory System Flashcards

Flashcards for Auditory System - from the Ears to the Brain

Sound wave

A wave of pressure changes that occurs in the air due to a vibrating source.

Medium (for sound)

Sound requires a medium to propagate.

Compression (sound wave)

Region of increased pressure in a sound wave.

Rarefaction (sound wave)

Region of decreased pressure in a sound wave.

Speed of sound in air

Approximately 344 m/s.

Pure tones

The simplest sounds, usually synthetic and look like a sine wave.

Amplitude

Physical measurement of sound intensity, related to loudness.

Micropascals (µPa)

Physical units for measuring sound intensity/amplitude.

Decibels (dB)

Logarithmic scale used to measure sound intensity.

Loudness

Perceived dimension of sound intensity.

Frequency

Physical measurement of cycles per second, measured in Hertz (Hz), related to pitch.

Pitch

Perceived dimension related to the frequency of a sound.

Hertz (Hz)

Cycles per second; unit of frequency.

Audible range (young adults)

20 - 20,000 Hz.

Infrasound

Frequencies below the human audible range.

Ultrasound

Frequencies above the human audible range.

Complex waveform

Most real-world sounds are complex.

Fundamental frequency

The lowest frequency of a complex waveform; generally dictates perceived pitch.

Harmonics

The higher frequencies of a complex sound (multiples of the fundamental); contribute to timbre.

Timbre

Difference in sound quality between two sounds with the same pitch and loudness.

Noise cancellation

Can be passively blocked (earplugs) or actively cancelled applying phase-reversal of same sound.

Pinna

External portion of the ear; funnels sound into the auditory canal.

Auditory canal (ear canal)

Funnels sound to the tympanic membrane.

Resonance in auditory canal

Amplifies sounds between 2,000 - 5,000 Hz.

Tympanic membrane (eardrum)

Airtight, elastic diaphragm that vibrates when hit by sound.

Eustachian tube

Thin tube connecting the middle ear to the pharynx to adjust air pressure in the middle ear.

Ossicles

Three tiny bones (malleus, incus, stapes) in the middle ear that transmit sound energy from tympanic membrane to inner ear.

Amplification in middle ear

Tympanic membrane and ossicles amplify sound by 20-30 dB.

Cochlea

Fluid-filled, snail-shaped structure in the temporal bone.

Oval window

Sound received via movement of stapes on oval window.

Vestibular and tympanic canals

Continuous with each other in the cochlea.

Cochlear duct

Middle canal in the cochlea where sensory transduction occurs.

Round window

Relieves pressure when exerted on oval window.

Organ of Corti

Auditory sensory organ located inside the cochlear duct.

Basilar membrane

Vibrates in response to incoming pressure waves; the Organ of Corti sits atop of it.

Tectorial membrane

Covers the hair cells in the Organ of Corti.

Base of basilar membrane

Thick, narrow, and stiff; responds to high frequencies.

Apex of basilar membrane

Thin, wide, and floppy; responds to low frequencies.

Characteristic frequency

The frequency that produces optimal vibration at different locations along the basilar membrane.

Outer hair cells

Three rows that indirectly influence sensory transduction.

Inner hair cells

Single row that performs sensory transduction.

Auditory nerve cells

Bipolar neurons with cell bodies in the spiral ganglion; their axons form the auditory/cochlear nerve.

Stereocilia

Hair-like structures on hair cells that bend (deflect) with basilar membrane movement.

Depolarization of hair cell

Occurs when mechanical ion channels open due to stereocilia bending.

Neurotransmitters in auditory system

Released by hair cells to excite auditory nerve fibers.

Spiral ganglion

Location of auditory nerve fiber cell bodies.

Place code

Frequency of sound is indicated by which auditory nerve fibers are firing.

Temporal code

Frequency of sound is indicated by the timing of auditory nerve fiber action potentials.

Tuning curve

Describes the responsiveness of an auditory nerve fiber to different frequencies.

Volley principle

Multiple nerve fibers fire for certain sound wave peaks, together representing the true frequency.

Place code frequency range

Works best for high frequencies (> 5,000 Hz).

Temporal code frequency range

Works best for low frequencies (< 500 Hz).

Population coding (amplitude)

Louder sounds will stimulate nerve fibers across characteristic frequencies and some auditory nerve fibers will be more sensitive than others.

Cochlear amplifier

A positive feedback loop that amplifies the traveling wave in the cochlea through the action of outer hair cells.

Audibility curve

Represents human sensitivity to sound across the audible spectrum.

dB HL

Decibels Hearing Level

Audiogram

A clinical graph expressing hearing thresholds across the tested frequencies.

Conductive hearing loss

Hearing loss resulting from damage to the outer or middle ear.

Sensorineural hearing loss

Hearing loss resulting from damage to the cochlea, auditory nerve, or primary auditory cortex.

Cochlear nucleus

Axons of the auditory nerve synapse in the cochlear nucleus of the brainstem.

Tonotopic organization

Organization of auditory areas by frequency, seen in many parts of the auditory nervous system.

Medial geniculate nucleus

Auditory nucleus of the thalamus.

Primary auditory cortex (A1)

Located on Heschl's gyrus in the temporal lobe; receives input from the thalamus.

Auditory core region

Sits on Heschl's gyrus, consisting of primary auditory cortex (area A1)

Belt and parabelt

Higher-order auditory cortex surrounding the core region; respond preferentially to complex sounds.

Dorsal auditory pathway

"Where" pathway; extends from core to posterior auditory cortex and then to posterior parietal cortex.

Ventral auditory pathway

"What" pathway; extends from core to belt and parabelt, and then to anterior temporal cortex and prefrontal cortex.

Azimuth

Horizontal angle from midline of head.

Elevation

Vertical angle from level of ears.

Distance (auditory)

Measured from center of the head.

Monaural cues

Cues for auditory distance and elevation.

Echoes

Useful distance cue.

Precedence effect

The first arriving sound usually dominate sound localization.

Doppler effect

Moving sound sources compress waves in front, spread out waves behind.

Spectral shape cue

Pinna-induced change of sound’s frequency spectrum.

Binaural cues

Require both ears for accurate sound localization.

Interaural level difference (ILD)

Lateralized sounds are louder in proximal ear.

Acoustic shadow

Head's acoustic shadow reduces intensity of sound in the far ear.

Interaural time difference (ITD)

Sound waves hit the two ears at slightly different times.

Auditory scene

All of the sounds that occur at a given time.

Auditory stream segregation

The process of separating an auditory mixture into distinct streams.

Auditory stream

Frequencies emitted over time by one sound source or related sound sources

Spectral segregation

A collection of grouping rules related to the use of frequency to group sounds together.

Harmonic coherence

Frequencies are grouped if they are harmonics.

Temporal segregation

Sounds that are linked in time are grouped together while sounds that are uncorrelated are not.

Temporal synchrony

Frequencies that begin, end, or change at the same time are grouped together.

Temporal proximity

Sequential sounds that are closer together in time are more likely to be grouped together.

Spatial segregation

Frequencies are grouped if they come from the same location.

Echolocation

The use of emitted sounds to get the position and the localization of an object.

Binaural Hearing

Hearing that uses both ears.

Monoaural localization

Using only one ear to localize the sound.

Vestibular canal

One of the canals in cochlea

Tympanic canal

One of the canals in the cochlea

Sound intensity

Related to amplitude

A1

Primary auditory cortex

High frequencies

Interaural level difference works best for high frequencies.

Low frequencies

Interaural timing difference works best for low frequencies

Mammalian Ears Advantages

Imbue better hearing

Auditory perception

Act of hearing

Brainstem

Axons of the auditory nerve synapse in the cochlear nucleus of the brainstem.