Development of sound localization

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Development of sound localization

• Acoustics, primary coding, neural computation
  could contribute to development of the ability to
  locate sound sources in space

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Topics in development of sound localization

• When can infants first locate sounds?
• How accurate is localization during development?
• How could the development of binaural cue
  processing contribute?
• Other distance perception and precedence effect

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Left-right discriminations
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Left-right discrimination Kittens
meow
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Left-right discrimination Rats
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Left-right discrimination Frequency effects
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Left-right discrimination Human infants
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Accuracy of localization during development
Minimum Audible Angle
Sound
Sound
Speakers
MAA
Sound
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MAA measured in several studies
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Changes in head size with age
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Acoustic consequences of a small head
400 µsec ITD
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IID and ITD discrimination Infants
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ITD discrimination Infants
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IID and ITD discrimination Children
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Localization in elevation depends on spectral cues
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Localization in elevation Infants
shh, shh, shh
16º
shh, shh
0º
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MAA in elevation Infants
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Sound localization involves three dimensions
elevation
azimuth
distance
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Distance perception Infants
Rattle, rattle
Rattle, rattle
Rattle, rattle
Rattle, rattle
Rattle, rattle
Rattle, rattle
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Distance perception Infants
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Precedence effect
?
click
click
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Precedence effect Infants
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Precedence effect Children
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Summary

• Young animals can localize at least grossly, soon
  after the cochlea starts to function.
• Human newborns can also localize sounds, but the
  MAA improves from birth to 5 years of age.
• Infants can localize sounds in all three spatial
  dimensions.
• Acoustics and interaural cue processing cannot
  fully account for the maturation of sound
  localization.
• Localization under simple conditions may be
  mature at 5 years of age, but under complex
  conditions, 5 year-olds are still immature sound
  localizers.

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Effects of experience on sound localization
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Pairing of visual and auditory information leads
to organization of sensory space.
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Effects of experience on localization by barn owls
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Critical period for spatial recalibration
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The critical period for re-adjusting after
unplugging is different!
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The more the owl uses his map, the longer it
remains plastic
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Effects of experience in humans Wilmington, Gray
and Jahrsdorfer (1994)

• 19 subjects with congenital unilateral atresia
• Tested before and after corrective surgery
• Age at surgery ranged from 6 to 33 years.
• Tests included ITD and IID discrimination, speech
  in noise (sound field), and sound localization.

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Interaural time discrimination after correction
of unilateral atresia
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Localization after correction of unilateral
atresia
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Chicks in auditory space
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Chicks maps of auditory space
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Speech in noise identification after correction
of unilateral atresia
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Summary of effects of experience on sound
localization

• Experience with sound is essential for the
  development of sound localization.
• Experience with sound is less essential for the
  development of the ability to process the
  acoustic cues to location.
• Although a critical period for the development of
  localization has been identified in some other
  species, a similar critical period has not yet
  been identified in humans.