29. localization Flashcards
Azimuth def?
- the location of a sound source in the HORIZONTAL plane
(side to side)
Elevation def?
- the location of a sound source in the MEDIAN (VERTICAL) plane
(up and down)
Distance def?
- how far a sound source is from the center of the head in any direction
Minimum audible angle def?
The minimum angular separation between a reference sound source and a different sound source (emitting a tone of the same frequency)
that yields 75% correct judgments about the relative horizontal positions of the two sources.
What 2 cues / pieces of information are there to perceive azimuth?
- Interaural LEVEL differences
- Interaural TIME differences
Interaural Level Differences:
- what does “level” mean?
- intensity, “loudness,” amplitude
Interaural Level Difference (ILD) def?
- Sound will have a lower volume at the ear that is farther from the sound source
Book def:
- Difference in sound intensity of the same sound at the two ears
Interaural Level Differences:
- what are the 2 things that contribute? Which one is super more important than the other?
- distance from sound makes sound quieter
–> head only inc. distance max 14 cm
–> only relevant with sounds very close to your head - acoustic shadow
Acoustic shadow def?
- head creates a “shadow” that partially blocks sound waves. This reduces the loudness of the sound on the opposite side of the head from the sound source
book def:
- An area on the other side of the head from a sound source in which the loudness of the sound is reduced because the sound waves are partially blocked by the head
Acoustic shadow more strongly affects high or low frequency sounds?
- HIGH frequency sounds!
- low frqs aren’t affected very much
Acoustic shadow:
what locations /degrees are…
- max?
- min/none?
Where 0º = straight forward…
Max: 90º, 270º (ie L / R)
Min/none: 0º, 180º (ie front / back)
Interaural time difference def?
The difference in arrival time of the same sound at the two ears
Interaural time difference:
does it work better for high or low frqs? Or all frqs equally?
- all frqs equally!
Interaural time difference:
Approx time diff. for 90º and 45º?
45º ≈ 300 microseconds
90º ≈ 600 microseconds
Neural basis of localization:
What brain structure does it happen in?
- the medial superior olive (MSO)
- both L&R MSOs receive signals from both L&R ears
Neural basis of localization:
- how does it work?
- What is it similar to in visual system?
- Neurons are tuned to diff. magnitudes of ITD
- they have time-delays in how fast signals from cochlear nucleus reach the neurons in MSO
- works similar to the mechanism for detecting motion in the visual system (with neuron 1 having a delay to get to neuron M)
Why are echoes often not noticeable? What “effect” does this relate to?
- direct sound source creates shortest path to you
- we localize sounds based on where they first arrive from
- relates to precedence effect
Precedence effect def?
localization is dominated by the sound that arrives first
Cone of confusion def?
- A hypothetical cone-shaped surface in auditory space with axis in auditory canals
- when two equally distant sound sources are located on the surface of a cone of confusion…
- they have highly similar ILD and ITD.
so, their locations are confusable
How do disambiguate ambiguous sounds?
(such as on a cone of confusion)
- move your head!
- moving your head changes the ILD and ITD
What is the cue used to determine elevation?
Spectral shape cue
Spectral shape cue def?
- shape of pinna changes amplification of sounds (depending on frq) based on their elevation
- we use this to judge elevation of a sound
Book def:
- pinna-induced modification in a sound’s frequency spectrum; amplifies and attenuates sounds of different frequencies at different elevations
Describe the important study about elevation? What was the main result?
- they mapped the spectral shape cue for a person’s pinna, then changed it by altering the shape of their pinna with inserts
- this completely ruined their ability to judge elevation
What effect would headphones have on localization? (without playing music)
- azimuth is fine
–> ITD is equal
–> ILD is muffled, but equal - elevation info is really limited
–> blocks the shape of the pinna
Visual capture / ventriloquism effect def?
- Visually apparent location of sound determines perceived location from which a sound originates
- when there’s conflicting visual & auditory into, visual system overrules auditory
Visual capture (affecting localization) is dependent on what 3 factors?
Visual and auditory events must be…
1. reasonably close in time
2. plausibly linked
3. plausibly close in space
–> earbuds & computer is good
–> comp. & speaker 2 rooms away is not
