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Frequency representation
The ability to use the spectrum or the fine structure of sound to detect,
discriminate, or identify sound.
Frequency representation
1. Development of frequency discrimination and frequency resolution
2. Development of mechanisms involved in frequency representation
Tasks involving frequency representation Frequency discrimination Masking Pitch and timbre perception Speech perception and much, much more.
Pure-tone frequency discrimination
Time
Fre
quen
cy
Which one was higher, 1 or 2?
Time
Fre
quen
cyDid you hear something change?
How do you get a baby to tell you that she heard something change?
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 infant’s response increases (“recovers”) then discrimination has occurred; if not, we don’t know anything.
Variations on habituation-based procedure Habituation (heart rate deceleration) High amplitude sucking Visual fixation
High amplitude sucking
Advantages and disadvantages of habituation-based procedures. Based on naturally
occurring infant responses
Relatively easy to get data from an infant
Can’t test adults as comparison
Can’t measure thresholds
Interpretation of negative result.
Depends on infant wanting to hear the sound you are studying.
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)
Variations on conditioned-response procedures Conditioned head-turn procedures
Visual Reinforcement procedures 2 spatial alternative procedures
Observer-based procedures
Observer-based methods
Advantages and disadvantages of conditioned-response methods Can test adults as
comparison Can measure
thresholds If the baby likes the
reinforcer, it doesn’t matter if he likes the sound
May need to train response in some infants (head turns)
May exclude infants who don’t meet control conditions.
Back to frequency representation
Pure-tone frequency discrimination
Time
Fre
quen
cyWhich one was higher, 1 or 2?
Time
Fre
quen
cy
Did you hear something change?
INFANTS CHILDREN (MOSTLY)ADULTS
Early studies of infant frequency discrimination
Wormith, S.J., D. Pankhurst, and A.R. Moffitt, Frequency discrimination by young infants. Child Dev, 1975. 46: p. 272-275
• 1-month-old infants• High amplitude sucking• 200 v. 500 Hz
Frequency discrimination at 3-12 months
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.
•3, 6, 12 months, adults•Observer based method•500, 1000, 4000 Hz jnd• adaptive thresholds
Frequency discrimination in older children
100
Low frequency
} conditioned response
Did those sound the same or different?
3 AFC
AXB
B
BB
B
JJJ
JJ
0.1
1
10
100
0.1 1 10 20Age (years)
B
BBB
H
H
JJJ
JJ
F
F
FF
ÑÑ
0.1
1
10
100
0.1 1 10 20Age (years)
B Olsho et al. (1987)
HSinnott and Aslin (1985)
JMaxon and Hochberg (1982)
FJensen and Neff (1993)
Ñ Hill et al 2005
High FrequencyLow frequency
B
BBB
H
H
JJJ
JJ
F
F
FF
ÑÑ
0.1
1
10
100
0.1 1 10 20Age (years)
B Olsho et al. (1987)
HSinnott and Aslin (1985)
JMaxon and Hochberg (1982)
FJensen and Neff (1993)
Ñ Hill et al 2005
Wier et al. 1977
Low frequency High frequency
Development of frequency discrimination
0.1
1
10
100
0.1 1 10 20
% c
ha
ng
e in
fre
qu
en
cy
Age (years)
LOW
High
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
Development of frequency resolution (place code) Thresholds in noise Psychophysical tuning curves Critical bandwidth Auditory filter width
The critical band concept
Development of thresholds in noise
Both frequency resolution and intensity resolution affect thresholds in noise
normal Bad intensity resolution
Bad frequency resolution
Critical bandwidth
Development of the critical bandwidth
Another measure of frequency resolution: Psychophysical tuning curve
?
Lev
el (
dB S
PL)
Frequency (Hz)800 1000
20
?
Lev
el (
dB S
PL)
Frequency (Hz)1000 1200
20
Infant psychophysical tuning curves
Auditory filter widths
Children’s auditory filter width
Hall and Grose to the rescue…
Hall and Grose to the rescue…
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 doesn’t mature until childhood, but low frequency resolution is mature in 3 month olds.
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.
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.