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Brain and Perception > Module 10 & 11 > Flashcards

Module 10 & 11 Flashcards

(109 cards)

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1
Q

What are compression and rarefaction?

A

Compression = high pressure; Rarefaction = low pressure

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2
Q

What moves through the air in a sound wave?

A

Pressure changes, not air molecules themselves.

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3
Q

What is the frequency of a sound wave?

A

The number of pressure cycles (compressions and rarefactions) per second.

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4
Q

Pure tone

A

The simplest periodic wave, defined by a sinusoid (sine wave) shape.

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5
Q

Amplitude and Loudness

A

The height from peak to trough of a sound wave. Determines how loud the sound seems. What we feel as sound strength. Increases with amplitude. Also depends on frequency (some pitches feel louder)

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6
Q

Complex Periodic Sounds

A

Real sounds (e.g., voice, instruments) = mix of sine waves

Waveform = complex but repeating shape

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7
Q

Anatomical Divisions Outer Ear

A

Outer Ear:

Pinna:
A cartilage-and-fat funnel with ridges that assist in sound localization.

Auditory Canal:
Approximately 25 mm long and 6 mm in diameter, directing sound to the eardrum and amplifying frequencies between 2–5kHz.

Tympanic Membrane (Eardrum):
A thin elastic diaphragm that vibrates in response to sound waves.

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8
Q

Anatomical Divisions Middle Ear

A

Middle Ear: An air-filled chamber behind the eardrum.

Ossicles: The three tiny bones—malleus, incus, and stapes—pick up and amplify the vibrations from the eardrum.

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9
Q

Anatomical Divisions Inner Ear:

A

Cochlea: A fluid-filled spiral structure where mechanical vibrations are converted into neural impulses by hair cells.

Semicircular Canals: Involved in balance and acceleration, not hearing.

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10
Q

Sound Pathway

A
  1. Sound waves are collected by the pinna and funnelled through the auditory canal.
  2. Vibrations from the sound waves strike the tympanic membrane, causing it to vibrate.

3.The ossicles transmit and amplify these vibrations, with the stapes footplate transmitting vibrations into the cochlear fluids.

  1. Hair cells in the cochlea convert these mechanical motions into electrical signals, which are sent via auditory nerve fibers to the brain.
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11
Q

What is the purpose of impedance-matching in the middle ear?

A

To amplify sound and overcome the loss when sound moves from air to fluid in the inner ear.

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12
Q

How does the area ratio help amplify sound?

A

The tympanic membrane is 15–20× larger than the oval window, focusing the force and increasing pressure.

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13
Q

How do the ossicles act as levers?

A

They convert a small force on the malleus into a larger force on the stapes.

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14
Q

Eustachian Tube

A

Connects the middle-ear cavity with the upper throat (nasopharynx). Normally closed; opens briefly during swallowing, yawning, chewing, or infant crying. Equalizes middle-ear air pressure with ambient pressure, restoring proper tympanic-membrane tension and normal hearing

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15
Q

Cochlea Anatomy - Three longitudinal chambers
(filled with fluid):

A

Overall shape: Snail-shaped, coiled tube (~33 mm uncoiled length; 5 mm diameter at base tapering to 2 mm at apex).

Three longitudinal chambers
(filled with fluid):

  1. Vestibular canal
    (scala vestibuli) – contains perilymph; begins at the oval window.
  2. Cochlear duct (scala media) – contains endolymph; houses the organ of Corti on the basilar membrane.
  3. Tympanic canal
    (scala tympani) – contains perilymph; ends at the round window.
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16
Q

Membranes of cochlea

A

Partitioning membranes:

Reissner’s membrane separates vestibular canal from cochlear duct.

Basilar membrane: separates cochlear duct from tympanic canal.

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17
Q

Helicotrema:

A

Apex opening connecting vestibular and tympanic canals, allowing perilymph pressure waves to circulate.

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18
Q

Round window:

A

Flexible membrane at the base of the tympanic canal that bulges outward to relieve pressure from fluid waves driven in by the stapes at the oval wind

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19
Q

What is the function of the basilar membrane in the cochlea?

A

It separates and analyzes sound frequencies through spatial tuning of traveling waves.

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20
Q

How does the basilar membrane respond at the base?

A

It is narrow, thick, stiff, and responds best to high frequencies.

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21
Q

How does the basilar membrane respond at the apex?

A

It is wide, thin, floppy, and responds best to low frequencies.

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22
Q

What causes traveling waves on the basilar membrane?

A

Perilymph pressure waves from sound vibrations.

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23
Q

What is a “characteristic frequency” on the basilar membrane?

A

The specific frequency that causes maximum displacement at a certain location.

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24
Q

How is the basilar membrane like a Fourier analyzer?

A

It spatially separates frequencies along its length, like decomposing a sound into its components.

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25
Where is the organ of Corti located?
On the basilar membrane, inside the scala media of the cochlea.
26
What is the role of inner hair cells (IHCs)?
To transduce sound into neural signals; connected to Type I fibers.
27
What is the role of outer hair cells (OHCs)?
To amplify and sharpen the response of inner hair cells; connected to Type II fibers.
28
What is the tectorial membrane?
A gelatinous structure that bends hair cell stereocilia during sound vibrations.
29
What percentage of auditory nerve fibers connect to IHCs vs. OHCs?
95% to IHCs (Type I); 5% to OHCs (Type II).
30
How are OHC stereocilia bent?
By shearing between the basilar and tectorial membranes.
31
How are IHC stereocilia bent?
By endolymph movement during basilar membrane vibration.
32
What are tip links?
Tiny fibers that connect stereocilia and open ion channels when stretched.
33
What ions flow in when tip links open channels?
K⁺ (potassium) and Ca²⁺ (calcium).
34
What is the result of ion influx into hair cells?
Depolarization, leading to neural signal generation.
35
What protein enables OHCs to contract and elongate?
Prestin, a voltage-sensitive membrane protein.
36
What triggers the motile response of OHCs?
Changes in membrane voltage (depolarization or hyperpolarization)
37
What is the effect of OHC motility on the basilar membrane?
It amplifies and sharpens vibrations, aiding in precise sound detection.
38
How much does OHC movement enhance basilar membrane motion?
By about 2–3%, which significantly improves sensitivity.
39
What do Type II auditory nerve fibers connect to? Are Type II fibers myelinated?
Outer Hair Cells (OHCs). No, they are thin and unmyelinated.
40
When do Type II fibers respond?What is the speculated function of Type II fibers?
To very intense, potentially damaging sounds. To detect painful or harmful sounds, like nociceptors in other sensory systems.
41
What is the place code for frequency?
The time between spikes reflects the frequency of the sound. Frequency is encoded by which part of the basilar membrane is most active.
42
What is the temporal code for frequency?
Frequency is encoded by the timing (phase-locking) of action potentials in Type I fibers.
43
Which frequencies are best encoded by the place code?
All frequencies, but especially high frequencies.
44
Which frequencies are best encoded by the temporal code?
Low frequencies (especially below 4,000 Hz).
45
What does a tuning curve show for an auditory nerve fiber?
The fiber’s sensitivity to different frequencies, especially its characteristic frequency.
46
What is tonotopy in the cochlea?
A frequency map: high frequencies at the base, low frequencies at the apex. This frequency map is preserved through all relay stations: Cochlear nucleus → Superior olive → Inferior colliculus → Medial geniculate nucleus → Primary auditory cortex (A1).
47
What is phase locking in temporal coding?
When nerve fibers fire in sync with the peaks of a sound wave.
48
How does temporal coding represent frequency?
By using spike timing to reflect the waveform’s periodicity.
49
What is the volley principle?
Multiple neurons alternate firing to represent high frequencies as a group.
50
When does temporal coding dominate over place coding?
For low to mid frequencies (below 5,000 Hz).
51
Why can’t a single nerve fiber encode the full range of sound amplitudes?
Its firing rate is limited, while we can hear sounds over 1 million μPa in range.
52
What is population coding in the auditory system?
Louder sounds recruit more fibers, even off-frequency ones, to encode amplitude.
53
What is dynamic range for a fiber?
The amplitude range between threshold and saturation.
54
How does the brain encode loudness across a wide range?
By combining many fibers with different thresholds and ranges.
55
What causes conductive hearing loss?
Problems in the outer/middle ear (e.g., earwax, eardrum damage, otitis media).
56
What causes sensorineural hearing loss?
Damage to the cochlea, auditory nerve, or central pathways (genetic or acquired).
57
What mechanical damage does loud noise cause in the cochlea?
Tears, stereocilia damage, and tip-link rupture.
58
What metabolic damage can occur with noise exposure?
Hair cell death due to glutamate toxicity, ischemia, and free radicals.
59
What does the acronym SONIC MG stand for in the auditory pathway?
Superior olive, Olivary nucleus, Nucleus cochlear, Inferior colliculus, Cochlear nucleus, Medial geniculate, → Auditory cortex
60
What is the function of the superior olivary nucleus?
Sound localization using binaural cues
61
What type of sounds activate the core auditory cortex (A1)?
Simple sounds like pure tones
62
What areas process complex sounds like vocalizations?
The belt and parabelt areas of the auditory cortex
63
What does the ventral (what) stream do?
Processes sound identity, projecting to the prefrontal cortex What (ventral): Origin: Anterior core +belt Pathway: Anterior temporal lobe →prefrontal cortex Function: Sound identification
64
What does the dorsal (where) stream do?
Processes sound location, involving the parietal lobe Origin: Posterior core +belt Pathway: Parietal lobe → prefrontalcortex Function: Sound localization
65
Where is the primary auditory cortex (A1) located? How the neurons are organized?
In the temporal lobe. In A1, neurons are organized left to right by best frequency (low → high).
66
Damage on A1
A1 is necessary for pitch perception. Bilateral damage to A1 → severe impairment in pitch-change detection and fine pitch discrimination
67
Where are pitch-sensitive neurons found in the auditory cortex? What do these pitch neurons respond to? What does this tell us about pitch perception?
In the lateral belt areas, outside A1. The perceived fundamental frequency, even if it’s missing from the sound. It involves higher-order cortical processing, not just early auditory areas.
68
What effect does pitch training have on auditory cortex?
It causes expansion and sharpening of frequency representation in A1 and belt areas.
69
What is the main (contralateral) auditory pathway from cochlea to cortex?
Cochlear nucleus → Inferior colliculus → MGB Contralateral Medial Geniculate Body→ Contralateral auditory cortex
70
Cochlear Nucleus (brainstem)
First relay for auditory nerve signals
71
Superior Olivary Complex (SOC) (brainstem)
Integrates signals from both ears ( binaural integration)
72
Inferior Colliculus (IC) (midbrain)
Main midbrain relay, integrates bilateral inputs
73
Medial Geniculate Body (MGB) (thalamus)
Final relay to auditory cortex Module
74
What firing pattern do inner hair cells and Type I fibers show?
Big initial burst, followed by sustained firing for preferred frequencies.
75
What types of firing patterns are seen in cochlear nucleus neurons?
Burst + adaptation, sustained, and gradual increase.
76
What do subcortical structures (e.g., SOC, IC, MGB) specialize in?
Precise timing and frequency coding for complex auditory input.
77
What is the purpose of inhibitory feedback to outer hair cells?
To reduce their movement and protect the cochlea from loud sounds.
78
What does the acoustic reflex do?
Causes ossicle muscle contractions to dampen loud sounds.
79
How does attention affect hearing?
Cortical feedback enhances important sounds and filters out irrelevant ones.
80
Where is the auditory cortex located?
Inside the lateral sulcus, on the temporal lobe.
81
What structure contains A1 and core auditory areas?
The transverse temporal gyrus (also called Heschl’s gyrus)
82
What are the belt and parabelt regions?
Surrounding areas of the auditory cortex involved in processing complex sounds.
83
Where are low vs. high frequencies mapped in A1?
Low = anterior, high = posterior
84
What do narrowly tuned A1 neurons respond to?
A specific frequency band, independent of loudness
85
How do broadly tuned A1 neurons behave?
Their response range widens with louder sounds, aiding in complex sound integration.
86
What kind of sounds do belt and parabelt areas prefer? What visual analogy fits the belt/parabelt regions?
Multi-frequency, meaningful sounds (e.g., speech), not simple tones. Like extrastriate visual areas, they process complex features, not just basic input.
87
Which auditory stream is associated with speech content and recognition?
The ventral (“what”) stream, via the anterior auditory cortex.
88
Which auditory stream helps locate and respond to sound sources?
The dorsal (“where”) stream, via the posterior auditory cortex.
89
What are the three dimensions of the auditory spatial coordinate system?
Azimuth (left–right), Elevation (up–down), Distance (near–far).
90
What does ILD stand for and what does it measure? How does the brain use ILDs to localize sound?
Interaural Level Difference—differences in sound intensity between the ears. Through a population code of neurons tuned to specific level differences.
91
What kind of sounds produce the strongest ILDs?
High-frequency sounds.
92
What does ITD stand for and what does it measure? What brain structure processes interaural time differences (ITDs)?
Interaural Time Difference—differences in arrival time of a sound at each ear. The medial superior olive (MSO).
93
What kind of sounds rely more on ITDs for localization?
Low-frequency sounds.
94
What is the "cone of confusion"?How does the brain resolve the cone of confusion?
A region where ILDs and ITDs are ambiguous, especially for front–back and elevation.: By using head movements to change ILDs and ITDs dynamically.
95
What does the pinna do to incoming sound?
It causes reflections that create spectral cues useful for elevation localization.
96
What is the inverse-square law in hearing?
Sound intensity decreases with the square of the distance from the source.
97
What is spectral blurring, and what does it indicate?
Loss of high-frequency detail in distant sounds → helps estimate distance.
98
How does reverberation help judge distance?
More direct sound = closer; more echo = farther.
99
What does the Doppler Effect tell us about moving sounds?
Higher pitch = approaching, lower pitch = receding; fastest shift = closest point.
100
How do MSO neurons work as coincidence detectors?
They fire when inputs from both ears arrive simultaneously.
101
What structure is involved in interaural level difference (ILD) processing?
The lateral superior olive (LSO) and higher regions like the auditory cortex.
102
What is an auditory stream?
A sequence of sounds perceived as coming from a single source.
103
Name one key cue used for auditory stream segregation.
Common onset/offset, timbre continuity, common fate, or spatial cues.
104
What does “common fate” mean in hearing?
Elements that change together over time are grouped as part of the same stream.
105
How is stream segregation similar to visual object perception?
Both rely on gradual change and synchrony to group features into coherent percepts.
106
What is harmonic coherence in auditory grouping?
Grouping of sounds with frequencies in a harmonic series (e.g., 220 Hz, 440 Hz).
107
How does synchrony affect sound grouping?
Synchronous sounds = grouped; asynchronous sounds = separated.
108
What is grouping by temporal proximity?
Sounds played close together in time group as one; with longer gaps, they are perceived as separate.
109
What is perceptual completion in hearing?
The brain "fills in" sounds interrupted by noise, making them seem continuous.

Brain and Perception (6 decks)

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