Chapter 10

Question 1

Sound waves

Answer 1

Mechanical displacement of molecules caused by changing pressure → waves of pressure changes in air molecules are sound waves

Question 2

Visualizing a sound wave

Answer 2

Air molecule density is plotted against time at a single point relative to the tuning forks right prong

Cycle: complete peak/valley → change from min/max air pressure to next min/max max air level, respectively

Resulting cyclical waves sine waves → every sound signal can be decomposed into waves

Question 3

Frequency and pitch perception

Answer 3

The rate at which sound waves vibrate is measured as cycles per second, or hertz (Hz)→the number of cycles that a wave completes in a given amount of time

Low frequency → low pitched sound

High frequency → high pitched sound

Each note in a musical scale has a different frequency

Question 4

Amplitude and perception of loudness

Answer 4

Intensity of sound is usually measured in decibels (dB)

High amplitude → loud sound

Low amplitude → soft sound

The magnitude of change in air molecule density

Normal human speech → 40 dB

Question 5

Complexity and timbre (perception of sound quality)

Answer 5

Most sounds are a mixture of frequencies

A sounds complexity determines its timbre, allowing us to distinguish → for example: a trombone from a violin playing the same note

Simple → pure tone

Complex → mix of frequencies (most waves)

Question 6

Hearing ranges among animals

Answer 6

Humans → 20 - 20,000 Hz

Whales and dolphins and dogs → 0 - 100,000 Hz

Rodents, bats, Birds, etc. → much less variation

Question 7

Breaking down complex tones

Answer 7

A number of pure tones give rise to complex waves which results in complex sound (think like colour theory)

Fundamental frequency → the rate at which the complex waveform pattern repeats (at regular intervals)

Overtones → set of higher-frequency sound waves that vibrate at whole-number multiples of the fundamental frequency

Periodicity → the fundamental frequency repeats at regular intervals: sounds that are aperiodic, or random, we call noise

Question 8

Perception of sound → basic

Answer 8

Auditory system converts the physical properties of sound wave energy to electrochemical activity → through transcluction so CNS can interpret →then processed by neurons in auditory system

Mechanical → electrochemical

Question 9

Properties of language and music as sounds

Answer 9

Left temporal lobe analyzes speech for meaning

Right temporal lobe analyzes musical sounds for meaning

Non speech and nonmusical noise produced at a rate of about 5 segments per second is perceived as a buzz → normal speed of speech is on the order of 8 to 10 segments per second (up to 30)

Segmentation: implicit mechanism that helps us know when a word begins and ends→ essential for understanding accents etc.

Question 10

Properties of language

Answer 10

Experience with a language helps with rapid speech

We hear variations of a sound as if they were identical → allows us to understand accents

The auditory system has a mechanism for categorizing sounds as the same despite small differences in pronunciation
→ makes learning foreign languages later in life more difficult because we are hardwired to understand language in a certain way

Question 11

Properties of music

Answer 11

Loudness, or amplitude, of a sound wave: subjective → what is loud to some is only moderately loud to others

Pitch: position of each tone on a musical scale; frequency of the sound wave → any pure note is perceived as the same regardless of the instrument

Quality: The timbre of a sound, regardless of pitch → you can distinguish between a trumpet and a piano sound » quality of these sounds differs

Question 12

Functional anatomy of the auditory system

Answer 12

The ear collects sound waves from the surrounding air

Converts mechanical energy to electrochemical neural energy

Routed through the brainstem to the auditory cortex

Auditory system is structured to decode frequency, amplitude, and complexity → some mechanism must locate sound waves in space

Neural systems for sound production and analysis must be closely related

Question 13

Anatomy of human ear

Answer 13

Outer ear → Pinna and ear canal

Middle ear → eardrum and malleus, incus, stapes (ossicles)

Inner ear → semicircular canals, cochlea, and auditory nerve

Question 14

Pinna

Answer 14

Funnel-like external structure designed to catch sound waves in the environment and deflect them into the ear canal

Question 15

External ear canal

Answer 15

Amplifies sound waves and directs them to the eardrum, which vibrates in accordance with the frequency of the sound wave

Question 16

Middle ear → ossicles

Answer 16

Air filled chamber that comprises the ossicles

Bones in the middle ear
↳ Hammer (malleus)
↳ Anvil (incus)
↳ Stirrup (stapes)

Connects the eardrum to the oval window of the cochlea, located in the inner ear

Question 17

Inner ear → cochlea

Answer 17

Fluid-filled structure that contains the auditory receptor cells

Organ of Corti: receptor hair cells and the cells that support these

Question 18

Inner ear → basilar membrane

Answer 18

Receptor surface in the cochlea that transduces sound waves to neural activity → scratches hair cells to produce reaction

Question 19

Inner ear → hair cells + tectorial membrane

Answer 19

Hair cells → specialized neurons in the cochlea tipped by cilia

Tectorial membrane → membrane overlying hair cells

Sound waves bend basilar membrane → cilia fire

Question 20

Basilar membrane → transducing sound waves into neural impulses

Answer 20

Sound waves produce a travelling wave that moves all along the basilar membrane → all parts of basilar membrane bend in response to incoming waves of any frequency

Basilar membrane is maximally responsive to frequencies mapped as the cochlea uncoils
↳high frequencies caused maximum displacement near the base of the membrane
↳ low frequencies caused maximum displacement near the membranes apex

Base → 20,000 Hz Apex → 100 Hz

When wave travels down basilar membrane, hair cells at the point of peak displacement are stimulated → maximal neural response in those cells

After incoming signal composed of many frequencies causes several points along the basilar membrane to vibrate → excites hair cells at all these points

Question 21

Auditory receptors

Answer 21

Transduction of sound waves to neural activity takes place in the hair cells

3500 inner hair cells (auditory receptors) → fixed #
12,000 outer hair cells (alter stiffness of tectorial membrane)

Movement of the basilar membrane stimulates the hair cells via bending and shearing action → causes AP and neural activity

Movement of cilia on hair cells changes membrane potential and alters neurotransmitter release

Question 22

Outer hair cells

Answer 22

Outer hair cells function by sharpening the cochlea’s resolving power, contracting or relaxing and thereby changing tectorial membrane stiffness → cilia attached to tectorial membrane

Outer hair cells amplify sound waves, providing an energy source that enhances cochlear sensitivity and frequency selectivity → creating mechanical changes in cochlea and cochlear fluid

Question 23

Inner hair cells

Answer 23

Animals with no inner hair cells are effectively deaf→ can only perceive very loud, low frequency sounds

Inner hair cells act as auditory receptors

Embedded in the basilar membrane (the organ of Corti) are tipped by cilia
↳movements of the basilar and tectorial membranes displace the cilia, leading to changes in the inner hair cells membrane potentials

Neurons in the auditory nerve have a baseline rate of firing
↳ rate is changed by neurotransmitters released by inner hair cell

No stimulation → still working at a baseline

Question 24

Movement of cilia

Answer 24

Movement of cilia in one direction depolarizes the cell, causing calcium influx and release of neurotransmitter → stimulates cells that form the auditory nerve » nerve impulses increase

Movement of cilia towards the opposite direction hyperpolarizes the cell, resulting in less neurotransmitter release → activity in auditory neurons decreases

Question 25

Pathways to the auditory cortex → LONG

Answer 25

Inner hair cells synapse on bipolar cells that form the auditory nerve (part of the 8th cranial nerve, which governs nearing and balance) → all connects to brainstem
↳ cochlear nerve axons enter the brainstem at the level of the medulla and synapse in the cochlear nucleus

The cochlear nucleus projects to the superior olive (a nucleus in the olivary complex) and the trapezoid body
↳ projections from the cochlear nucleus connect with cells on BOTH hemispheres of the brain » mixes input from the 2 ears for single sound perception

The cochlear nucleus and the superior olive send projections to the inferior colliculus in the dorsal midbrain

The inferior colliculus goes to the medial geniculate nucleus (thalamus)
↳ ventral region of the medial geniculate nucleus projects to the primary auditory cortex, area A1
↳ dorsal region projects to the auditory cortical regions adjacent to area A1

Analogous to the visual system are two distinct pathways in the auditory system

One identifies objects by their sound characteristics (temporal lobe/ventral stream → WHAT)

Other directs movements by the sounds heard (posterior parietal lobe/dorsal stream → HOW)

Question 26

Auditory cortex

Answer 26

Primary auditory cortex, A1, lies within heschl’s gurus, surrounded by secondary cortical areas A2 → secondary cortex behind heschls gurus is called Planum Temporale

The cortex of the left planum forms a speech zone: Wernicke’s area

The cortex of the larger, right hemisphere heschls gyrus has a special role in analyzing music

Right handed → Heschl is larger in left hemisphere

Question 27

Lateralization

Answer 27

Process whereby functions become localized primarily on one side of the brain

Analysis of speech takes place largely in the left hemisphere (Broca’s and Wernicke’s area)

Analysis of musical sounds takes place largely in the right hemisphere

Question 28

Insula → language and taste

Answer 28

Located within the lateral fissure; multifunctional cortical tissue containing regions related to language, to the perception of taste, and to the neural structures underlying social cognition

Injury to the insula can produce disturbances of both language and taste

Question 29

Left-handed people and audition

Answer 29

About 70% are similar to right-handers → having language in the left hemisphere

In remaining 30% speech is represented either in right hemisphere or bilaterally

Does not change perception of sound and music

Unsure of what drives difference

Question 30

Neural activity and hearing → hearing pitch

Answer 30

Hair cells in the cochlea code frequency as a function of their location on the basilar membrane → largest level of displacement

The tonotopic representation of the basilar membrane is reproduced in the cochlear nucleus

This systematic representation is maintained throughout the auditory pathways and into the primary auditory cortex

Similar tonotopic maps can be constructed for each level of the auditory system

Question 31

Tonotopic representation

Answer 31

Structural organization for processing of sound waves from lower to higher frequencies → matches mapping found in cochlea

Question 32

Tonotopic representation of A1

Answer 32

Low Frequency (corresponds to apex of cochlea) → High Frequency (corresponds to base of cochlea)

Question 33

Detecting loudness

Answer 33

The greater the amplitude of the incoming sound waves, the higher the firing rate of bipolar cells in the cochlea

More intense sound waves trigger more intense movements of the basilar membrane

Causes more shearing action of the hair cells

Leads to more neurotransmitter release onto bipolar cells

Question 34

Detecting location

Answer 34

Estimate location of a sound both by taking cues derived from one ear and by comparing cues received at both ears
↳each cochlear nerve synapses on both sides of the brain to locate each sound source

Neurons in the brainstem compute the difference in a sound waves arrival time at each ear → the interaural time difference (ITD)

Another mechanism for source detection is relative loudness on the Left and right → the interaural intensity difference (IID)

Question 35

Detecting location → medial superior Olivary Complex

Answer 35

Cells in each hemisphere receive inputs from both ears and calculate the difference in arrival times between the two ears

More difficult to compare the inputs when sounds move from the side of the head toward the middle → the difference in arrival times is smaller

When we detect no difference in arrival times, we infer that the sound is coming from directly in front or behind us

Question 36

Detecting location → lateral superior olive and trapezoid body

Answer 36

Source of sound is detected by the relative loudness on the left or right side of the head

Since high-frequency sound waves do not easily bend around the head, the head acts as an obstacle

As a result, higher-frequency sound waves on one side of the head are louder than on the other

Question 37

Locating a sound

Answer 37

Compression waves originating on the left side of the body reach the left ear slightly before reaching the right

The ITD is small but the auditory system can discriminate it and fuse the dual stimuli

So that we perceive a single, clear sound coming from the left

Question 38

Detecting patterns in sound

Answer 38

Music and language are perhaps the primary sound wave patterns that humans recognize

Ventral pathway decodes spectrally complex sounds (auditory object recognition) including the meaning of speech sounds for people

Dorsal auditory stream integrates auditory and somatosensory information to control speech production (audition for action)
↳ less known about neurons in the dorsal stream

Question 39

Uniformity of language structure

Answer 39

All languages have common structural characteristics stemming from a genetically determined constraint

Language is universal in human populations

Humans learn language early in life, seemingly without effort
→ likely a sensitive period for language acquisition that runs from about 1-6 yrs of age

Languages have many structural elements in common
→ example: syntax and grammar

Question 40

Brocas Area → localizing language

Answer 40

Anterior speech area in the left hemisphere that functions with the motor cortex to produce movements needed for speaking

Thought → wernickes area → brocas area → facial area of motor cortex → cranial nerves → speak

Question 41

Wernicke’s Area → localizing language

Answer 41

Posterior speech area at the rear of the left temporal lobe that regulates language comprehension

Also called the posterior speech zone

Spoken word → A1 → wernicke’s area → comprehension of word

Question 42

Brocas aphasia

Answer 42

Inability to speak fluently despite having normal comprehension and intact vocal mechanisms

Disconnect between language comprehension and production

Question 43

Wernickes aphasia

Answer 43

Inability to understand or produce meaningful language even though the production of words is still intact

Speaks fluently but makes no logical sense → word salad

Question 44

Brain stimulation → auditory cortex

Answer 44

Penfield used weak electrical current to stimulate the brains surface

Patients reported hearing various sounds (e.g., ringing that sounded like a doorbell, buzzing noise, birds chirping)

Question 45

Brain stimulation → A1

Answer 45

Produced simple tones → ex. ringing sounds

Question 46

Brain stimulation → wernickes area

Answer 46

Apt to cause some interpretation of a sound

Ex: buzzing sound to a familiar source such as a cricket

Question 47

Disrupting speech → Brain stimulation mapping

Answer 47

Supplementary speech area on the dorsal surface of the frontal lobes stops ongoing speech completely → speech arrest

Question 48

Eliciting speech → Brain stimulation mapping

Answer 48

Stimulation of the facial areas in the motor cortex and the somatosensory cortex produces some localization related to movements of the mouth and tongue

Question 49

Auditory cortex mapped by PET → Hypothesis

Answer 49

Zatorre and colleagues → hypothesized that simple auditory stimulation, such as bursts of noise, are analyzed by area A1, whereas more complex auditory stimulation, such as speech syllables, are analyzed in adjacent secondary auditory areas
↳ Wernicke and Brocas area

Also hypothesized that performing a discrimination task for speech sounds would selectively activate left-hemisphere regions

Question 50

Auditory cortex mapped by PET

Answer 50

Passively listening to noise bursts activates the primary auditory cortex → A1

Listening to words activates the posterior speech area, including Wernicke’s area

Making a phonetic discrimination activates the frontal region, including Broca’s area

Both types of stimuli produced responses in both hemispheres but with greater activation in the left hemisphere for the speech syllables

A1 analyzes all incoming auditory signals, speech and nonspeech, whereas the secondary auditory areas are responsible for some higher-order signal processing required for analyzing language sound patterns

Question 51

Processing music

Answer 51

Largely a right-hemisphere specialization

The left hemisphere plays some role in certain aspects of music processing, such as those involved in making music

→ recognizing written music, playing instruments, and composing: LH

Question 52

Localizing music → Zatorre and colleagues: PET study

Answer 52

Passively listening to noise bursts activates Heschl’s gyrus

Perception of melody triggers major activation in the right-hemisphere auditory cortex → A2

Making relative pitch judgments about two notes of each melody activates a right frontal lobe area

Question 53

Music as therapy

Answer 53

Music is used as a treatment for mood disorders such as depression

The best evidence of its effectiveness lies in studies of motor disorders → such as stroke and Parkinson disease

Listening to rhythm activates the motor and premotor cortex and can improve gait and arm training after stroke

Parkinson patients who step to the beat of music can improve their gait length and walking speed

Question 54

Birdsong

Answer 54

Many nonhuman animals communicate with other members of their species by using sound

Birdsong functions → attracting mates, demarcating territories, and announcing locations

Question 55

Parallels between birdsong and language

Answer 55

Song development in young birds is influenced by both genes and early experience/learning

Gene-experience interactions are epigenetic mechanisms

Brain areas that control singing in adult sparrows show altered gene expression in spring as the breeding and singing season begins

Both appear to be innate yet are shaped by experience

Humans seem to have a template for language that is programmed into the brain, and experience adds a variety of specific structural forms to this template

If a young bird is not exposed to song until is is a juvenile and then listens to recordings of birdsongs of various species, the young bird shows a general preference for its own species song

Question 56

Whale songs

Answer 56

Cetaceans (whales, dolphins, and porpoises) have evolved to use a variety of AM and FM sounds for several different communication purposes → LOW frequency sounds

The humpbacked whales songs are composed of a set of predictable and regular sounds that bear striking similarities to human musical traditions