Kuhl, P. K., Williams, K. A., Lacerda, F., Stevens, K. N., & Lindblom, B.
(1992) Linguistic experience alters phonetic perception in infants by 6
months of age. Science, 255, 606-608.
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All vowel sounds largely characterized by relative frequencies of F1 & F2
Different languages have different sets of vowel sounds
– They carve up F1/F2 "space" differently
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F1/F2 "space" with some
English vowel variants
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Kuhl et al. (1992) Presentation
Magnet Effect
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Adult speakers of a language agree quite well about best examples of vowels in
their language are
– i.e., they agree on prototypical vowels for the language
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Adults show a magnet effect around prototypical vowels in their language
– Similar to categorical perception for consonants, but less extreme
– Give adults pairs of vowel sounds & ask them to rate how similar they sound
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Sometimes one member of the pair is a prototypical vowel from their language
Sometimes neither sound is a prototype
Degree of physical difference sometimes small, sometimes large
For equivalent size physical difference, people judge sounds near a prototype as
more similar to it than sounds near a non-prototype
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Prototypes in F1/F2 space act like "magnets“
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Given variability in speech (due to both co-articulation and error), this "tuning"
probably allows us to ignore unimportant variations as long as they're close
enough
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Kuhl et al. (1992) Presentation
How early in life does this "tuning" for specific
languages happen?
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Use habituation paradigms to test what infants can discriminate
– sucking rate, heart rate, head-turning
– play an auditory stimulus repeatedly and then change it and observe
behavior
– training phase:
• make large change in stimulus & present visual display child likes at same
time to 1 side
• child begins to anticipate visual display whenever sound changes, so now
only turn on display after they've turned their head - the display is a reward
for turning
– test phase:
• change stimuli by differing amounts, & use head-turning as indication of
whether child noticed change
• head-turn is analogous to adults' similarity ratings
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Evidence from these paradigms that categorical perception for consonants
becomes adult-like by about 1 year of age (Werker & Tees, 1984)
– Hypothesized that this is because infants typically start to produce
single words at 8 to 12 months, & that starting to use sounds
meaningfully is what gives rise to the tuning effect
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Kuhl et al. (1992) Presentation
Study
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32 American & 32 Swedish 6-month-old infants tested
– in US and Sweden in monolingual families
Head-turning habituation paradigm
Vowel sounds were English /i/ & Swedish /y/
– English doesn't have /y/ & Swedish doesn't have /i/, so there's 1 sound
that's a prototype for each language and 1 that isn't
- Stimuli were synthesized
vowel sounds varying in
distance from prototype
(& non-prototype)
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Kuhl et al. (1992) Presentation
Results
• Infants showed "magnet effect" for their
prototype but not for the other vowel
– American infants "didn't notice" the
change in vowel sound (i.e., they didn't
turn):
• 67% of the time when it was near /i/
• 51% of the time when it was near /y/
– Swedish infants "didn't notice" the
change:
• 56% of the time when it was near /i/
• 66% of the time when it was near /y/
• Infants "hear vowels close to prototype for their language as sounding
like prototype"
• This is already developing by 6 months of age
• Thus, it's not dependent on beginning to speak, but simply on experience
hearing the language
09/01/10
Kuhl et al. (1992) Presentation