Frequency representation

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Frequency representation

• The ability to use the spectrum or the fine
  structure of sound to detect, discriminate, or
  identify sound.

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Frequency representation

1. Development of frequency discrimination and
   frequency resolution
2. Development of mechanisms involved in frequency
   representation

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Tasks involving frequency representation

• Frequency discrimination
• Masking
• Pitch and timbre perception
• Speech perception and much, much more.

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Pure-tone frequency discrimination
Frequency
Frequency
Time
Time
Which one was higher, 1 or 2?
Did you hear something change?
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How do you get a baby to tell you that she heard
something change?
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Habituation-based procedures

• One stimulus or type of stimulus is presented to
  the infant repeatedly.
• The infant responds to the stimulus in some way,
  but on repeated presentations the response
  decreases (habituates).
• Once habituation has occurred, the stimulus is
  changed.
• If the infants response increases (recovers)
  then discrimination has occurred if not, we
  dont know anything.

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Variations on habituation-based procedure

• Habituation (heart rate deceleration)
• High amplitude sucking
• Visual fixation

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High amplitude sucking
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Advantages and disadvantages of habituation-based
procedures.

• Based on naturally occurring infant responses
• Relatively easy to get data from an infant

• Cant test adults as comparison
• Cant measure thresholds
• Interpretation of negative result.
• Depends on infant wanting to hear the sound you
  are studying.

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Conditioned response procedures

• The stimulus is a sound or a change in an ongoing
  sound, but it serves as a signal to the infant
  that he should respond.
• If the infant responds when he hears this
  signal, he gets to see something interesting
  (e.g., a mechanical toy or video comes on)

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Variations on conditioned-response procedures

• Conditioned head-turn procedures
• Visual Reinforcement procedures
• 2 spatial alternative procedures
• Observer-based procedures

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Observer-based methods
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Advantages and disadvantages of
conditioned-response methods

• Can test adults as comparison
• Can measure thresholds
• If the baby likes the reinforcer, it doesnt
  matter if he likes the sound

• May need to train response in some infants (head
  turns)
• May exclude infants who dont meet control
  conditions.

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Back to frequency representation
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Pure-tone frequency discrimination
CHILDREN (MOSTLY) ADULTS
INFANTS
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Early studies of infant frequency discrimination

• 1-month-old infants
• High amplitude sucking
• 200 v. 500 Hz

Wormith, S.J., D. Pankhurst, and A.R. Moffitt,
Frequency discrimination by young infants. Child
Dev, 1975. 46 p. 272-275
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Frequency discrimination at 3-12 months

• 3, 6, 12 months, adults
• Observer based method
• 500, 1000, 4000 Hz jnd
• adaptive thresholds

Olsho, L.W., E.G. Koch, and C.F. Halpin, Level
and age effects in infant frequency
discrimination. J Acoust Soc Am, 1987. 82 p.
454-464.
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Frequency discrimination in older children
conditioned response


100
Did those sound the same or different?
3 AFC
AXB
Low frequency
High Frequency
Low frequency
High frequency
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Development of frequency discrimination

LOW
High
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Possible explanations for differences in
development of low and high frequency
discrimination

• It takes longer to learn low frequency
  discrimination and infants/kids need even more
  practice than adults.
• The codes for low and high frequencies develop
  differently

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Development of frequency resolution (place code)

• Thresholds in noise
• Psychophysical tuning curves
• Critical bandwidth
• Auditory filter width

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The critical band concept
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Development of thresholds in noise
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Both frequency resolution and intensity
resolution affect thresholds in noise
normal
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Critical bandwidth
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Development of the critical bandwidth
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Another measure of frequency resolution
Psychophysical tuning curve
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Infant psychophysical tuning curves
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Auditory filter widths
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Childrens auditory filter width
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Hall and Grose to the rescue
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Hall and Grose to the rescue
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Conclusions so far

• Both high frequency discrimination and high
  frequency resolution are immature in listeners
  younger than 6 months of age, and mature in
  listeners older than 6 months.
• Low frequency discrimination doesnt mature until
  childhood, but low frequency resolution is mature
  in 3 month olds.

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Why is low-frequency discrimination immature?

• Temporal code could be immature
• No psychophysical evidence for or against
• Temporal code could be mature, but infants and
  children may take awhile to learn to use this
  information.

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Development of frequency representation

• Frequency resolution, the accuracy of the place
  code for frequency, is immature at birth.
• Frequency resolution is adultlike by 6 months of
  age.
• The development of the temporal code for
  frequency is less well understood.