Christine L. Stager

Infants listen for more phonetic detail in speech perception than in word-learning tasks.

Infants aged 4–6 months discriminate the fine phonetic differences that distinguish syllables in both their native and unfamiliar languages, but by 10–12 months their perceptual sensitivities are reorganized so that they discriminate only the phonetic variations that are used to distinguish meaning in their native language. It would seem, then, that infants apply their well honed phonetic sensitivities as they advance and begin to associate words with objects, but the question of how speech perception sensitivities are used in early word learning has not yet been answered. Here we use a recently developed technique to show that when they are required to pair words with objects, infants of 14 months fail to use the fine phonetic detail they detect in syllable discrimination tasks. In contrast, infants of 8 months—who are not yet readily learning words—successfully discriminate phonetic detail in the same task in which infants aged 14 months fail. Taken together, these results suggest a second reorganization in infantss use of phonetic detail as they move from listening to syllables to learning words.

Language Experience and the Organization of Brain Activity to Phonetically Similar Words: ERP Evidence from 14- and 20-Month-Olds

The ability to discriminate phonetically similar speech sounds is evident quite early in development. However, inexperienced word learners do not always use this information in processing word meanings Stager & Werker (1997). Nature, 388, 381382. The present study used event-related potentials (ERPs) to examine developmental changes from 14 to 20 months in brain activity important in processing phonetic detail in the context of meaningful words. ERPs were compared to three types of words: words whose meanings were known by the child (e.g., bear), nonsense words that differed by an initial phoneme (e.g., gare), and nonsense words that differed from the known words by more than one phoneme (e.g., kobe). These results supported the behavioral findings suggesting that inexperienced word learners do not use information about phonetic detail when processing word meanings. For the 14-month-olds, ERPs to known words (e.g., bear) differed from ERPs to phonetically dissimilar nonsense words (e.g., kobe), but did not differ from ERPs to phonetically similar nonsense words (e.g., gare), suggesting that known words and similar mispronunciations were processed as the same word. In contrast, for experienced word learners (i.e., 20-month-olds), ERPs to known words (e.g., bear) differed from those to both types of nonsense words (gare and kobe). Changes in the lateral distribution of ERP differences to known and unknown (nonce) words between 14 and 20 months replicated previous findings. The findings suggested that vocabulary development is an important factor in the organization of neural systems linked to processing phonetic detail within the context of word comprehension.

Additive effects of phonetic distinctions in word learning

While infants have been demonstrated to be sensitive to a wide variety of phonetic contrasts when tested in speech discrimination tasks [Eimas et al. (1971) et seq.], recent work [Stager and Werker (1997)] has shown that following habituation to a word–object pairing, infants of 14 months fail to notice when the place of articulation of the initial consonant is switched [b/d]. Using the same procedure, the present study has found that infants do not respond to a change in voicing [b/p]. They do, however, notice a switch between dissimilar words [lɪf/nim]. One interpretation of these findings is that 14‐month‐olds do not encode either place or voice distinctions in lexical representations, so that words differing in only these features are treated as identical. To test this hypothesis, the effect of combining featural contrasts is currently being investigated by examining whether infants do respond to a change in both place and voice [d/p]. If there is such an additive effect, the contrasts must be represe...

Updates on becoming a native listener

Infants’ sensitivity to the sound structure of the native language becomes finely honed during the first year. New studies confirm and extend this fact in the domains of phonetic, metrical, and grammatical processing. First, infants were tested on their ability to discriminate phonetic, but nonmeaningful differences in the native language. Although most 6‐ to 8‐month olds discriminated [d] versus [t], 10‐ to 12‐month olds did not. Thus, by 10–12 months, infants listen to only those phonetic differences that distinguish acceptable native‐language syllabic shapes. Next, English‐learning infants’ discrimination of single syllable words such as ‘‘clone’’ from their WS counterparts, e.g., ‘‘cologne’’ was examined. Testing infants from the newborn period through the first year of life revealed that this ability is not robustly evident until around 10 months. Finally, the authors asked whether infants are sensitive to the acoustic and phonological cues distinguishing content from function words. Using lists of c...

Phonetic perception and word learning: Evidence for continuous and discontinuous changes

The purpose of this symposium is to describe recent research investi between Infant speech perception and early word learning. 9 ating the link In our talk we wil first briefly review the well established fact that within the first year of life infants move from easily discrimtnating both native and non-native phonetic contrasts, to onl Y-u3 contrasts. Our question is whether this change sets t being able to easily discriminate native stage for word learning. We will present two sets of studies, one that reveals a fair amount of continuity between experiential changes in speech perception abilities and the antecedents to word recognition, and one that sug ests a discontinuity between the phonetic sensitivites demonstrated n speech perception an % wordobject association tasks.