Frequency representation The ability to use the spectrum or the fine structure of sound to detect, discriminate, or identify sound. Frequency representation 1. 2. Development of frequency discrimination and frequency resolution Development of mechanisms involved in
frequency representation Tasks involving frequency representation Frequency discrimination Masking Pitch and timbre perception Speech perception and much, much more.
Frequency Frequency Pure-tone frequency discrimination Time Which one was higher, 1 or 2? Time Did 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 infants response increases (recovers) then discrimination has occurred; if not, we dont 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 Cant test adults as comparison Cant 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 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. Back to frequency representation Pure-tone frequency discrimination CHILDREN (MOSTLY) ADULTS Frequency
Frequency INFANTS Time Did you hear something change? Time Which one was higher, 1 or 2? 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 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. Frequency discrimination in older children } F F
B H B 100 J J F J J J
F B H B Olsho et al. (1987) H Sinnott and Aslin (1985)
J Maxon and Hochberg (1982) Did those sound the same or different? F Jensen and Neff (1993) 3 AFC
Hill et al 2005 AXB conditioned response Wier et al. 1977 100 100 1
10 20 Low frequency Age (years) Low frequency Highfrequency Frequency High Low frequency F F
10 B B H B 1 J 10
1 Age (years) Olsho et al. (1987) H Sinnott and Aslin (1985) B J F J
J J F 0.1 0.1 B 10
B H 20 1 0.1 0.1 J Maxon and Hochberg
B B (1982) F Jensen and Neff (1993) Hill et al 2005 J
B J J J J 1 Age (years) 10 20
Development of frequency discrimination 100 % change in frequency 10 LOW 1 High
0.1 0.1 1 Age (years) 10 20 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 frequency resolution Bad intensity resolution Critical bandwidth Development of the critical
bandwidth Level (dB SPL) Another measure of frequency resolution: Psychophysical tuning curve Level (dB SPL) 20 ? 1000 1200
Frequency (Hz) 20 ? 800 1000 Frequency (Hz) Infant psychophysical tuning curves
Auditory filter widths Childrens 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 doesnt 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.
