09/01/10 Kuhl et al. (1992) Presentation 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, 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 F1/F2 "space" with some English vowel variants

09/01/10 Kuhl et al. (1992) Presentation Magnet Effect 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 & 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 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

09/01/10 Kuhl et al. (1992) Presentation How early in life does this "tuning" for specific languages happen? 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 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

09/01/10 Kuhl et al. (1992) Presentation Study 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)

09/01/10 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