Problem 8 - DONE

Question 1

auditory localisation

Answer 1

= locating of sound sources in auditory space

• auditory space = exists all around
• -> created by each sound in a room/sounds all around
• -> each sound is heard as coming from different locations

Question 2

localisation cues

Answer 2

= information used to determine auditory location
- created by way sound interacts with listener’s head + ears (pinnae)
two kinds:
(1) binaural cues
(2) monaural cues

Question 3

three dimensions of sound

Answer 3

1. azimuth = extends from left to right
2. elevation = extends up and down
3. distance = distance of sound source from the listener

Question 4

binaural cues

Answer 4

= information reaching both ears
- locate along azimuth coordination
- based on comparison of sound signals reaching the left + right ears
=> sounds that are off to the side: reach one ear before the other (1) + louder at one ear than the other (2)
(1) inter-aural time difference (ITD)
(2) inter-aural level difference (ILLD)
–> superior olivery nuclei

Question 5

inter-aural time difference (ITD)

Answer 5

= difference between when a sound reaches the one ear and when it reaches the other; phase delays

• location of low-frequency sounds (< 1500 Hz)
• source directly in front of listener: distance to each ear is the same/sound reaches the left and right ears simultaneously
• -> ITD = 0
• source is located off to the side: sound reaches right/left ear before it reaches the other
• -> ITD becomes larger as sound sources are located more to the side
• magnitude of ITD: cue to determine sound’s location

Question 6

inter-aural level difference (ILD)

Answer 6

= difference in the sound pressure level (amplitude/loudness) of the sound reaching the two ears; intensity
- location of high-frequency sounds (> 1500 Hz)
- acoustic shadow = head is a barrier
–> reducing intensity of sounds that reach the far ear (for high-frequency, not low)
=> high-frequencies: (small compared to size of head) are disrupted by head
=> lower frequencies: smaller difference between the ILDs for sounds coming from two locations
=> very low frequencies: ILD is a very poor indicator of a sound’s location

Question 7

cone of confusion

Answer 7

= ITD + ILD illustrate ambiguous places
- ITD/ILD differences can be the same at different elevations
=> no reliable indication of elevation of sound source (only azimuth, distance)
solution:
- move our heads: additional ITD/ILD + spectral information
–> helps locate continuous sounds

Question 8

monaural cues

Answer 8

= information from one ear

• locate sounds along elevation coordinate
• spectral cues

Question 9

spectral cues

Answer 9

= information for localisation is contained in differences in distribution (spectrum) of frequencies that reach each ear from different locations
cause:
- reflection from head and within folds of pinnae before stimulus enters auditory canal
–> importance of pinnae: nooks and crannies of pinnae makes it easy to locate sounds along the elevation coordinate

Question 10

jeffress neural coincidence model

Answer 10

= proposes that neurones are wired so they receive signals from two ears

• coincidence detectors = only fire when both signals coincide by arriving at same time at neurone
• proposes: series of detectors, each tuned to respond best to a specific ITD
• -> place code = ITD is indicated by place (which neurone) where activity occurs

Question 11

ITD tuning curves

Answer 11

= plots neurone’s firing rate against ITD

- measure properties of ITD neurones, because each respond best to certain ITD

Question 12

broadly tuned neurones

Answer 12

• in right hemisphere: respond when sound comes from the left
• in left hemisphere reason when sound comes from the right
• location of sound: indicated by ratio of responding of these two types of broadly tuned neurones
• distributed coding = determined by firing of many broadly tuned neurones working together

Question 13

auditory pathways

Answer 13

• from temporal lobe to frontal lobe
• what pathway
• where pathway

Question 14

what pathway

Answer 14

• starts: anterior part of score + belt
• extends: prefrontal cortex
• -> identifying sounds

Question 15

where pathway

Answer 15

• starts: posterior part of core + belt
• extends: prefrontal cortex
• -> locating sounds

Question 16

auditory scene analysis

Answer 16

= multiple sound sources in auditory scene are separated into sound images
- no spatial information on auditory receptors
problem:
- sounds from different sources are combined into single acoustic signal
–> difficult to tell which part of signal is created by which source (just by looking at waveform of sound stimulus)
- uses spectral cues + ITD + ILD

Question 17

segregation principles

Answer 17

• similar to Gestalt in vision
• perceptually organise elements of auditory scene
• basis: how sounds occur in environment

Question 18

location

Answer 18

= information about where each source is located

• -> separate sounds based on localisation cues (ITD, ILD)
• when a source moves: continuous movement of sound (rather than jumping from one to another place)
• -> perceive sound from a passing car as originating from a single source

Question 19

onset time

Answer 19

= if two sounds start at slightly different times: likely that they came from different sources

• in environment: sounds from different sources rarely start at exactly the same time
• when sound components start together: likely that created by same source

Question 20

pitch and timbre

Answer 20

= same timbre or pitch: often produced by same source

Question 21

auditory continuity

Answer 21

= sounds that stay constant/change smoothly are often produced by the same source

• Gestalt principle: good continuation
• -> sound stimuli with same frequency/smoothly changing frequencies are perceived as continuous even when interrupted by another stimulus = continuity illusion

Question 22

experience

Answer 22

= effect of past experience on perceptual grouping

- melody schema = representation of a familiar melody that is stored in a person’s memory

Question 23

localisation in A1 and belt area

Answer 23

• neurones in A1: respond when sound is moved within specific area of space + don’t respond outside that area
• neurones in posterior belt area: respond to sound within an even smaller area of space
  –> spatial tuning is better
  => neurones in belt area provide more precise information than A1 neurones about location

Question 24

auditory stream segregation

pitch and timbre

Answer 24

= separation of different sound sources into perceptually different streams
–> depends on pitch and rate at which tones are presented

Question 25

scale illusion

auditory illusions

Answer 25

= melodic channeling = effect in which notes in each ear jump up and down, making listener perceive smooth sequence of notes
–> accurately interpret what is happening in the environment