Lecture 7: Hearing, Auditory Processing, and Vestibular Balance

What does the auditory system detect?

Miniscule air movements and processes them into a rich perceptual world.

What is the role of the vestibular system?

It detects head movement and is responsible for the sense of balance.

Where is the vestibular sensory organ located?

Within the inner ear alongside the auditory organ.

Why did the auditory system evolve?

It provides useful information about environmental objects and events, enhancing survival and reproductive success.

What are acoustic cues?

Sounds made incidentally as animals move through their environment.

What are acoustic signals?

Sounds evolved specifically to convey information and influence the behavior of receivers.

How do acoustic signals function in social groups?

They broadcast individual identity and are vital for recognition in social animals.

What unique calls do vervet monkeys use?

'Leopard' calls for climbing trees and 'eagle' calls for hiding in bushes.

What is echolocation?

A process where animals produce vocalizations to detect environmental obstacles and prey.

How do sound waves interact with objects?

Acoustic waves travel slower and have longer wavelengths than visible light waves.

What is the function of the tympanic membrane?

It vibrates in response to minute air pressure variations in the ear canal.

What mechanical advantage do the middle ear ossicles provide?

They facilitate impedance matching to transfer airborne vibrations into cochlear fluid.

What are the three compartments of the cochlea?

Scala vestibuli, scala tympani, and scala media.

What is tonotopy?

Frequency-to-position mapping along the basilar membrane representing spatial dimensions.

What is the role of inner hair cells?

They convert mechanical acoustic energy into neural electrochemical signals.

What do outer hair cells do?

They function as active mechanical amplifiers for low-intensity sounds.

What is the significance of prestin in outer hair cells?

It drives electromotive shape changes, enabling rapid cellular movements.

What is conductive hearing loss?

Hearing loss resulting from acoustic transmission deficits, such as eardrum damage.

What is sensorineural hearing loss?

Hearing loss involving hair cell or auditory nerve damage, which is irreversible in mammals.

What is the approximate prevalence of hearing loss in people aged 12 and older in the U.S.?

It affects one in eight people.

What happens to outer hair cells when overstimulated?

They become vulnerable to damage, impairing frequency selection and speech intelligibility.

What is the role of the basilar membrane?

It separates complex sounds into component frequencies along a logarithmic map.

What are periodic sounds?

Sounds that compress and rarefy air at specific frequencies described by sinusoids.

What distinguishes aperiodic sounds from periodic sounds?

Aperiodic sounds lack repeating patterns and contain random fluctuations perceived as noise.

How do acoustic waves propagate?

Through air molecule compression and rarefaction, creating ripples.

What is the significance of vocal tract filtering?

It alters speech resonance to produce distinct vowel sounds.

What is the range of human audible frequencies?

20 to 20,000 Hz.

What is the relationship between sound wavelengths and object size?

Acoustic waves exhibit diffraction around objects similar in size to their wavelength.

What type of hearing loss is caused by damage to hair cells or the auditory nerve?

Sensorineural hearing loss

What can excessive noise exposure cause in the auditory system?

Severe shearing forces on basilar and tectorial membranes

What is tinnitus?

Phantom sound perception resulting from central neural overcompensation

How does the auditory system determine sound source location?

By using head-centered spatial coordinates

What does azimuth represent in sound localization?

The horizontal angle to the left or right of the head midline

What does elevation represent in sound localization?

The vertical angle above or below the horizontal plane

Where is spatial localization acuity highest?

Directly in front of the head along the horizontal axis

What role do bilateral ear placements play in sound localization?

They provide slightly different acoustic inputs to calculate source location

What do interaural level differences arise from?

The head casting an acoustic shadow

What is the speed of sound at sea level?

343 m/s

What is the primary brainstem structure processing azimuthal location?

The superior olivary complex

What do medial superior olive (MSO) and lateral superior olive (LSO) compare?

MSO compares timing, while LSO compares levels

What is perceived as loudness along a geometric logarithmic decibel scale?

Acoustic amplitude

How is sound frequency perceived?

As pitch, where doubling frequency produces a one-octave interval

What do otolith organs detect?

Linear acceleration and gravity orientation

What are the three semicircular canals responsible for?

Sensing angular acceleration

What is the function of the vestibulo-ocular reflex (VOR)?

To maintain stable visual gaze during head rotation

What do cerebellar Purkinje cells modulate?

VOR reflex gain based on target distance and visual cues

What is the role of the vestibular labyrinth?

To sense dynamic acceleration forces and static gravitational forces

What is the function of the crista ampullaris in the semicircular canals?

To sense angular acceleration by bending hair cell stereocilia

What do spectral notches created by auricle ridges indicate?

Sound source elevation

What is the significance of interaural time delays?

They serve as primary spatial localization cues for low-frequency sounds

What do multi-peak neurons in the auditory cortex integrate?

Input across multiple harmonic frequencies

What do ascending projections from vestibular nuclei control?

Postural balance and gaze maintenance during head rotation

What is the role of otoconia in the otolith organs?

To provide weight in the gelatinous matrix for detecting orientation

What is the effect of velocity changes on the vestibular system?

They produce dynamic forces of acceleration proportional to net force

What is the primary function of the auditory cortex?

To store short-term and long-term acoustic memories