Sebastián-Gallés, N. & Bosch, L. (2009)

Developmental shift in the discrimination of vowel contrasts in bilingual infants: is the distributional account all there is to it?

PSYC 525Ji Young Kim

Fall, 2010

Background• A shift from language-general to language-specific

discrimination in 6-month-old infants.

• Discriminability reduced around prototypical exemplars of native vowel categories, while discrimination was still preserved for exemplars around non-prototypical vowels

• Statistical account: through continuous exposure to the native language and language-specific mapping alters perception.

• Most studies address the question of perceptual reorganization processes in groups of monolingual infants.

Bosch & Sebastián-Gallés (2003)•Catalan and Spanish mid front vowels

• Catalan: /e/ and /ɛ/• Spanish: /e/

• Discrimination was available by 4 months of age, but evidence of this capacity could not be obtained at 8 months of age. However, 12-month-old bilingual infants were eventually able to reach discrimination for this specific vowel contrast.

Þ U-shaped pattern. Different developmental time- course

Bosch & Sebastián-Gallés (2003) cont’d

• Infants’ phonetic analyses of the bilingual input might converge in a shared perceptual space, common to both languages.

• Spanish /e/ falls in between Catalan /e/-/ɛ/ and is used with much higher frequency than the two Catalan vowels (around 30% in Spanish and 8% in Catalan)

Þ Formation of a single extended category which temporarily masks the discrimination of the Catalan pair of contrastive elements.

• Through continued exposure to Catalan and Spanish, bilingual infants would eventually form smaller subcategories within this broader mid-front vowel space, thus reaching discrimination at a later age.

Burns, Yoshida, Hill & Werker (2007)•English-French VOT distinction of /ba/ and

/pa/

• The precise location of the boundary differs in the two languages.

• English: short-lag [ba] vs. long-lag [pha]• French: pre-voiced [ba] vs. short-lag [pa]

• The acquisition of phonological categories in monolingual and bilingual infants was equivalent.

Þ No U-shape pattern. Equivalent developmental time- course

Bosch & Sebastián-Gallés(2003) vs. Burns et al.(2007)

•Bruns et al. (2007): Difference between the results could be explained in terms of both frequency and distribution of the different speech sounds.

•Spanish /e/ > Catalan /e/-// •English /b/-/p/ = French /b/-/p/

Þ This would prevent the speech perception system of bilinguals from aggregating /b/ and /p/ into a single category.

Sebastián-Gallés & Bosch (2009)•Spanish and Catalan back vowels /o/-/u/

• Contrastive in both languages• Distribution: low density region between /o/ and /u/ categories• Frequency: Spanish (/o/>/u/) Catalan (/u/ >/o/.vowel reduction)

Hypothesis• If frequency and distributional properties

are the only driving forces to build up phoneme categories, then 8-month-old Spanish-Catalan bilingual infants should not have had any trouble in keeping the /o/–/u/ categories separate.

Experiment 1Participants

• 24 monolingual and 24 bilingual 4- and 8-month-old infants

• 12-month-old bilingual infants• Criteria: language(s) spoken by parents, estimate

of the hours of daily exposure to the language(s)Þ Monolingual: at least 80% of daily exposure

to the family language (Catalan or Spanish)Þ Bilingual: range from 50%–50% to 65%–35%

of daily exposure to Catalan and Spanish

Procedures

• Discriminate the natural exemplars of the target [‘doði] – [‘duði] pseudo-words, which were recorded by six different female speakers using a motherese style.

Þ Discrimination based on perceptual normalization of highly variable word-shaped stimuli

• Familiarization-preference procedure Familiarization phase (12 stimuli of same

target word)Test phase (6 similar tokens+ 6 novel tokens)

• Image on the center monitor to capture the attention; as soon as the infant began to look at it, this image disappeared and a different image appeared on one of the two side monitors. When the infant was looking in that direction, the presentation of the test stimuli began and continued until its completion or until the infant ceased to look for more than 2 consecutive seconds.

• Recorded attentional responses and duration of infants’ visual fixation

Results

• All 4-month-old infants discriminated the contrast (significantly longer attention times) • Only monolingual 8-month-olds showed discrimination behavior• Bilingual infants regained discrimination behavior at 12 months of age Þ U-shape pattern

Experiment 2• Too perceptually demanding??• Less varied stimuli

2a. Reduced talker variability (2 speakers) 2b. Reduced complexity of stimuli

(monosyllabic/do/-/du/) produced by a single speaker

Results• Even in these very restricted situations, bilingual 8-

month-olds failed to show discrimination behavior.

Discussion•If frequency and distributional properties

are the only driving forces to build up phoneme categories, then 8-month-old Spanish-Catalan bilingual infants should not have had any trouble in keeping the /o/–/u/ categories separate.

Þ No. Other variables need to be considered as well.

Future study• Degree of lexical similarity of the

languages of exposure (cognate words with different pronunciation especially in vowels)• Type of phoneme contrast (different

processing units)•Certain degree of overlap of maximum

and minimumF1 and F2 values for /o/ and /u/ in Spanish(no difficulties have been observed in the monolingual group)

•Role of socio-indexical factors (one parent-one language strategy)

•Actual acoustic-phonetic properties of bilingual adult productions (in some circumstances, bilinguals’ categories are ‘deflected’ away to maintain contrasts existing in their L1 and L2, while in other situations bilinguals’ productions are a compromise between L1 and L2 categories. (Flege, 1995))

•Specific characteristics of infant-directed speech (IDS) in bilingual environments.