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.
Background:
- All vowel sounds are largely characterized by relative frequencies of F1 and F2
- Different languages have different sets of vowel sounds: they carve up the F1/F2 "space" differently
- F1/F2 "space" with some English vowel variants:
- 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
- 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 and ask them to rate how similar they sound
- 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
- Prototypes in F1/F2 space act like "magnets"
- Given the amount of variability in speech production (due to both co-articulation and error), this
"tuning" probably allows us to ignore unimportant variations as long as they're close enough
Question:
- How early in life does this "tuning" for specific languages happen?
Susan Garnsey - Psyc / Ling / Comm 525 Presentation – 09/01/10
- 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, and use head-turning as indication of whether child
noticed change
- head-turn is analogous to adults' similarity ratings
- There's 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, and that starting to use sounds meaningfully is what gives rise to the tuning effect
Study:
- 32 American and 32 Swedish 6-month-old infants tested
- in US and Sweden in monolingual families
- Head-turning habituation paradigm
- Vowel sounds were English /i/ and Swedish /y/
- English doesn't have /y/ and Swedish doesn't have /i/, so there's one sound that's a prototype
for each language and one that isn't
- Stimuli were synthesized vowel sounds varying in distance from prototype (and non-prototype)
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/
Conclusions:
- Infants "hear vowels close to a prototype for their language as sounding like the 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
Susan Garnsey - Psyc / Ling / Comm 525 Presentation – 09/01/10