Task 8: Auditory Localization

Question 1

Auditory localization

Answer 1

Locating of sound sources in auditory space.

Question 2

Name the 2 dimensions in which sounds can be located in addition to distance

Answer 2

1. azimuth = left to right

2. elevation = up to down

Question 3

Name the 2 cues for localization

Answer 3

1. binaural

2. monaural

Question 4

Binaural cues

• define
• name 2 examples

Answer 4

Uses information reaching both ears to determine azimuth of sounds e.g. ITD + ILD

Question 5

Interaural time difference (binaural cue)

Answer 5

Difference between when sound reaches left ear and when it reaches right ear. Provides information about location of low-frequency sounds.
-> ITD becomes larger as sources are located more to the side. When distance is equal, ITD is equal

Question 6

Interaural level difference (binaural cue)

Answer 6

Difference in sound pressure level of sound reaching two ears.

• Acoustic shadow: reduces intensity of sounds reaching far ear.
• Reduction of intensity occurs only for high-frequency sounds because if object is larger than distance between waves, it has higher effect than if object is smaller.

Question 7

Cone of confusion

Answer 7

Time and level differences provide info that enables us to judge location along azimuth, but they provide little info about elevation of sound source.

Question 8

Monaural cue

Answer 8

one ear to determine elevation

Question 9

Define spectral cue

Answer 9

Information for localization is contained in differences in distribution (spectrum) of frequencies reaching each ear from different locations
- best for judging elevation at high frequencies

Question 10

Directional transfer function

Answer 10

Explains how head, pinna and ear canal change intensity of sounds with different frequencies arriving at each ear from different locations in space (azimuth and elevation).

Question 11

Superior olivary nucleus

Answer 11

place where signals from left and right ears meet

Question 12

Inferior colliculus

Answer 12

place where further binaural processing occurs

Question 13

A1

Answer 13

signal arrive here, travel to other cortical auditory areas (core, belt and parabelt areas)

Question 14

What do neurons of the belt area do?

Answer 14

provide more precise information than A1 neurons about location of sound sources

Question 15

Jeffress neural conicidence model of auditory localization

Answer 15

model that proposes that neurons are wired so they each receive signals from two ears (blue is left ear and red is right)

Question 16

Coincidence detectors

Answer 16

Neurons that only fire when both signals coincide by arriving at same time at neuron.

Question 17

ITD tuning curves

Answer 17

Curve that plots neuron’s firing rate against ITD. Useful to measure properties of ITD neurons, because each respond best to certain ITD.

Question 18

What kind of neurons is coding for localization based on? Where are they? What does the amount of firing indicated

Answer 18

• Broadly tuned neurons
• Right hemisphere when responding to sound on left and vice versa
• How much these neurons fire indicates the location of sound. If sound is in left side, right hemispheric neurons respond faster

Question 19

Distributed code

Answer 19

Code of localization for mammals because ITD is determined by firing of many broadly tuned neurons working together.

Question 20

Name the 2 auditory pathways extending from temporal to frontal lobe

Answer 20

What and where

Question 21

What pathway

• location
• responsibility
• neurons
• effect of deactivation

Answer 21

• Anterior part of core and belt and extends to prefrontal cortex
• Responsible for identifying different types of sounds.
• Neurons in anterior belt respond to more complex sounds.
• Deactivating disrupts ability to distinguish two patterns of sounds

Question 22

Where pathway

• location
• responsibility
• neurons
• effect of deactivation

Answer 22

• Posterior part of core and belt and extends to prefrontal cortex.
• Associated with locating sounds.
• Neurons in posterior belt have better spatial tuning than those in A1.
• Deactivating disrupts ability to localize sounds

Question 23

Sound waves from all sound sources in environment are summed into ______ But our auditory system can distinguish events or objects

Answer 23

single complex wave

Question 24

Auditory scene analysis

Answer 24

Process by multiple sound sources in auditory scene are separated into sound images.

Question 25

Name 5 seperating sources to help us perceptually organise auditory scences

Answer 25

1. location
2. onset time
3. pitch and timbre
4. auditory continuity
5. experience

Question 26

Location

Answer 26

To analyze auditory scene into separate components, we can use information about where each source is located

• sounds can be separated based on localization cues e.g. ITD and ILD
• when source moves, it follows continuous path

Question 27

Onset time

Answer 27

If two sounds start at different times, it is likely that they came from different sources, if so more likely to group tones by spatial location

Question 28

Pitch & Timbre

Answer 28

Sounds that have same timbre or pitch range are often produced by same source.

Question 29

Auditory stream segregation

Answer 29

Separation of different sound sources into perceptually different streams. It depends on pitch and rate at which tones are presented.

Question 30

Grouping by similarity of pitch

- what illusion is associated?

Answer 30

Instrument plays notes alternating rapidly between high and low tones, creating perception of two separate melodies. High and low notes are perceived to be playing by two different instruments.

• scale illusion

Question 31

Explain the scale illusion

Answer 31

Effect in which notes in each ear jump up and down, making listener perceive smooth sequence of notes.

Question 32

Auditory continuity

Answer 32

Sound stimuli with same frequency or smoothly changing frequencies are perceived as being continuous even when interrupted by another stimulus (good continuation principle). Longer than a certain period and it stops.

Question 33

Experience

Answer 33

When people know which melody is present, they compare what they hear to their stored schema and perceive melody.

Question 34

Melody schema

Answer 34

Representation of familiar melody that is stored in person’s memory.

Question 35

Acoustic startle reflex

Answer 35

Very rapid motor response to abrupt loud sound. It is unselective, so any loud sound produces this effect.
-> Time between ear (sound) and spinal cord (movement) is brief – Very few neurons are involved in basic startle reflex.

Question 36

Inattentional deafness

- limitation?

Answer 36

When we attend to particular sound source strongly and miss out on hearing other sounds.
- When surrounding sounds are made sufficiently loud, listeners had more trouble focusing in particular sound.

Question 37

Why is it misleading to group componenets of an orchestra by location?

Answer 37

due to reflections therefore must rely on other cues

Question 38

What cues do we rely on to differentiate between orchestral sounds? x 3

Answer 38

1. harmonicity
2. timing
3. pitch proximity

Question 39

Harmonicity

Answer 39

When two complex tones are played simultaneously by instruments built on same fundamental (unison) or different fundamentals they will be fused and only one tone will be perceived
- degree of fusion depends on frequency between fundamentals (complex tones fuse best when played in perfect unison with a 1:1 ratio and second best at an octave 2:1)

octave: same pitch but double frequency

Question 40

Continuous frequency modulation

Answer 40

Natural sounds generated by instruments undergo small frequency fluctuations that preserve ratios formed by their component frequencies.

Question 41

Pitch proximity

Answer 41

Hearer tends to link successive tones that are close in pitch and separate those that are further apart.

• tempo: the faster the tempo between 2 varying pitches, the smaller the threshold pitch difference at which one perceives separate streams
• frequency: when frequency difference between tones is small, we perceive ‘galloping’ rhythm. When difference is increased, two unrelated streams of tones are heard.

Question 42

Theory of unconscious inference in perception

Answer 42

When faced with complex configuration, our perceptual system adopts most plausible interpretation in terms of our knowledge of environment. Similar sounds are likely to be coming from same source and different sounds from different sources