Infant Speech Perception & Language Processing

Languages of the World Similar and Different on many features Similarities –Arbitrary mapping of sound to meaning –System of rules for combining sounds (phonology) –System of rules for combining words (syntax) –System of rules for relating the two (includes morphology) But languages differ in how they solve each of these problems

Meanings of Words Languages differ in the information encoded in verbs –Some languages, such as English, encode “manner” in motion –Other languages, such as many Oceanic languages, encode “path” in motion

Phonemic inventories vary

Segments, but also Tones Segments are the phonetic units like consonants, vowels, etc. We distinguish words in English by changing segments (e.g. pat vs. bat) Many languages of the world also use tones to distinguish meaning (e.g. ma rising vs. ma falling)

Grammatical Categories English has prepositions Many other languages have postpositions

Grammatical Markers In English we use “s” to indicate plural Some First Nations languages use “reduplication” of the final consonant to indicate plural Japanese requires a grammatical construct

Basic Word Order English is primarily Subject-Verb-Object Many other languages are primarily Subject-Object-Verb (and in some can drop the object) A few (e.g. Japanese, OVS)

Rhythmicity languages have been commonly grouped into distinct rhythmic classes: –stress-timed (English, Dutch, Russian, Arabic, etc) –syllable timed (French, Spanish, Italian, Greek etc.) –mora timed (Japanese, Tamil etc.) idea that linguistic rhythm is based on the isochrony of different constituents This did not hold; new idea % vowel &  consonant

Getting Started…. Do infants need to learn to perceive these characteristics after birth? Or are they born with a sensitivity to them? If born with it – is it innate, or is it learned/acquired during prenatal development?

Rhythmicity Infants at 4 months can discriminate native from non-native languages But only if from different rhythmical classes And only if played forward Moreover, they appear to prefer their native language

Age related changes During the next several months –Become able to discriminate languages from within a rhythmical class –Even two dialects of the same language –But only if it is the rhythmical class to which they are exposed –Bilingual infants can discriminate languages from within a rhythmical class at 4 months of age

What is learned? Is the ability to discriminate languages learned? Is it species specific? Why does it only occur for forwards speech?

What do cotton top tamarins do? Can also discriminate languages from different rhythmical classes And only if played forward Are not known to prefer any particular language What does this tell us about the origins of rhythm perception?

Tuning to the Native Language: Segments Young infants discriminate similar sounding consonants and vowels, including those not used in the native language By 1 year of age, selective sensitivity to just those contrasts used to distinguish meaning in the native language (Werker & Tees)

English Stop Consonants Hindi Stop Consonants

The Conditioned Head Turn Task

English and Hindi adults: Discrimination

Age changes in non-native discrimination (Werker & Tees)

Replications & extensions in other labs Salish and Zulu consonants, Best, et. al. 1994; behavioural tasks Estonian vs. Finnish vowels, Cheour, et. al., 1998; ERP task Chinese fricatives and English laterals, Kuhl, et. al., 2002; behavioural and ERP tasks

Extending to Bilinguals: English and French Tracey Burns, McVie, & Werker (BUCLD, 2003) Stimuli: – [ba] [pa] [p h a] Fr. /ba/ Fr./pa/-Eng /ba/ Eng /pa/ - Habituated to the middle [pa], and tested with [ba] and [p h a]

Testing mono- and bilingual infants: months For vowels, see Bosch & Sebastian-Galles, 2000; in press

Summary Bilingual Study –6 month olds have the same category boundary irrespective of language of input – Infants 10 Months + from monolingual homes place the category boundary in the appropriate location for their native language –10 month olds from bilingual homes do not appear to categorize the stimuli –by 14 months + bilinguals show clear patterns: About half perceive the stimuli as either English (n=4) or French (n=1) monolinguals The other half discriminate both contrasts

What causes the change? Word learning Perceptual learning –If so, what mechanism?

One Possible Mechanism: Statistical Learning Jusczyk showed that by 9-10 months infants are familiar with many of the properties of the native language This includes phonotactics and stress This seems to be driven by frequency in the input Suggests infants are sensitive to statistical information

In 1996 Saffran, Aslin, & Newport showed that infants can indeed use statistics to segment words from continuous speech In particular, by 8 months of age infants can use the transitional probabilities between syllables to pull out those syllable sequences that constitute a word

Statistical Learning in our lab: Jessica Maye, Werker, & Gerken (Cognition, 2002) Could infants sensitivity to distributional information the change in speech perception performance in the first year of life? Test infants of 6- and 8-months of age. These are both ages when infants should still be open to the characteristics of the input Previous work has shown statistical learning at 8 months

Manipulating the Input: Presentation frequency during familiarization

Single fixation statistical learning task Familiarization Phase –Infants shown a display of a field of flowers –Infants heard 6 blocks of 24 syllables each –Each block had 16 stimuli from the da-ta continuum and 8 filler items –Frequency of presentation of each item corresponded to either the uni- or bimodal distribution –The 2.3 familiarization phase continued whether the infants looked or looked away

Single fixation statistical learning task Test Phase –Infants shown a checkerboard –Two types of test trials: 4 Alternating Trials: Stimuli 1 and 8 4 Non-alternating Trials: Either Stimulus 3 or 6 –Each 11 sec trial contained 8 stimuli at 1 sec ISI –If infants can discriminate the two types of test trials, they should show differential looking

The looking procedure

Results Alternating trials(s) Non-Alternating trials (s) 6 mos. Unimodal 4.85 (SE = 0.33) 4.53 (SE = 0.39) 8 mos. Unimodal 4.98 (SE = 0.40) 5.20 (SE = 0.40) * 6 mos. Bimodal 5.66 (SE = 0.37) 6.41 (SE = 0.30) * 8 mos. Bimodal 5.45 (SE = 0.36) 6.15 (SE = 0.38)

Implications Infants may use the statistics of the distribution of information in the input to tune phonetic categories. This may be the mechanism that leads to the formation of native language phonetic categories Further research is necessary to see if this form of learning leads to lasting changes, and if it generalizes to language use.

Prosodic Bootstrapping Do the changes in speech perception in the first year of life help bootstrap language acquisition?