Lack of early sensitivity and gradual emergence of native phoneme categories: A pattern from underrepresented language learners.

Perceptual narrowing of speech perception supposes that young infants can discriminate most speech sounds early in life. During the second half of the first year, infants' phonetic sensitivity is attuned to their native phonology. However, supporting evidence for this pattern comes primarily from learners from a limited number of regions and languages. Very little evidence has accumulated on infants learning languages spoken in Asia, which accounts for most of the world's population. The present study examined the developmental trajectory of Korean-learning infants' sensitivity to a native stop contrast during the first year of life. The Korean language utilizes unusual voiceless three-way stop categories, requiring target categories to be derived from tight phonetic space. Further, two of these categories-lenis and aspirated-have undergone a diachronic change in recent decades as the primary acoustic cue for distinction has shifted among modern speakers. Consequently, the input distributions of these categories are mixed across speakers and speech styles, requiring learners to build flexible representations of target categories along these variations. The results showed that among the three age groups-4-6 months, 7-9 months, and 10-12 months-we tested, only 10-12-month-olds showed weak sensitivity to the two categories, suggesting that robust discrimination is not in place by the end of the first year. The study adds scarcely represented data, lending additional support for the lack of early sensitivity and prolonged emergence of native phonology that are inconsistent with learners of predominant studies and calls for more diverse samples to verify the generality of the typical perceptual narrowing pattern. RESEARCH HIGHLIGHTS: We investigated Korean-learning infants' developmental trajectory of native phoneme categories and whether they show the typical perceptual narrowing pattern. Robust discrimination did not appear until 12 months, suggesting that Korean infants' native phonology is not stabilized by the end of the first year. The prolonged emergence of sensitivity could be due to restricted phonetic space and input variations but suggests the possibility of a different developmental trajectory. The current study contributes scarcely represented Korean-learning infants' phonetic discrimination data to the speech development field.

Developmental differences in the hemodynamic response to changes in lyrics and melodies by 4- and 12-month-old infants.

Songs and speech play central roles in early caretaker-infant communicative interactions, which are crucial for infants' cognitive, social, and emotional development. Compared to speech development, however, much less is known about how infants process songs or how songs affect their development. Lyrics and melody are two key components of songs, and much of the research on song processing has examined how the two components of the songs are processed. The current study focused on the roles of lyrics and melody in song perception, by examining developmental patterns and the ways in which lyrics and melody are processed in the infants' brains using near-infrared spectroscopy (NIRS). The results revealed that developmental changes occur in infants' processing of lyrics and melody in a similar timeline as perceptual reorganization, that is, from 4.5 and 12 months of age. We found that 4.5-month-olds showed a right hemispheric advantage in the processing of songs that underwent a change in either lyrics or melodies. Conversely, 12-month-olds showed significantly higher activation bilaterally when lyrics and melody changed at the same time. These results suggest that 4.5-month-olds processed songs in the same manner as music without lyrics. Moreover, 12-month-olds processed lyrics and melody in an interactive manner, a sign of a more mature processing method. These findings highlight the importance of investigating the independent development of music and language, and also considering the relationship between speech and song, lyrics and melody in song, and speech and music more broadly.

The Effects of Lexical Pitch Accent on Infant Word Recognition in Japanese.

Learners of lexical tone languages (e.g., Mandarin) develop sensitivity to tonal contrasts and recognize pitch-matched, but not pitch-mismatched, familiar words by 11 months. Learners of non-tone languages (e.g., English) also show a tendency to treat pitch patterns as lexically contrastive up to about 18 months. In this study, we examined if this early-developing capacity to lexically encode pitch variations enables infants to acquire a pitch accent system, in which pitch-based lexical contrasts are obscured by the interaction of lexical and non-lexical (i.e., intonational) features. Eighteen 17-month-olds learning Tokyo Japanese were tested on their recognition of familiar words with the expected pitch or the lexically opposite pitch pattern. In early trials, infants were faster in shifting their eyegaze from the distractor object to the target object than in shifting from the target to distractor in the pitch-matched condition. In later trials, however, infants showed faster distractor-to-target than target-to-distractor shifts in both the pitch-matched and pitch-mismatched conditions. We interpret these results to mean that, in a pitch-accent system, the ability to use pitch variations to recognize words is still in a nascent state at 17 months.

Language-general biases and language-specific experience contribute to phonological detail in toddlers' word representations.

Although toddlers in their 2nd year of life generally have phonologically detailed representations of words, a consistent lack of sensitivity to certain kinds of phonological changes has been reported. The origin of these insensitivities is poorly understood, and uncovering their cause is crucial for obtaining a complete picture of early phonological development. The present study explored the origins of the insensitivity to the change from coronal to labial consonants. In cross-linguistic research, we assessed to what extent this insensitivity is language-specific (or would show both in learners of Dutch and a very different language like Japanese), and contrast/direction-specific to the coronal-to-labial change (or would also extend to the coronal-to-dorsal change). We measured Dutch and Japanese 18-month-old toddlers' sensitivity to labial and dorsal mispronunciations of newly learned coronal-initial words. Both Dutch and Japanese toddlers showed reduced sensitivity to the coronal-to-labial change, although this effect was more pronounced in Dutch toddlers. The lack of sensitivity was also specific to the coronal-to-labial change because toddlers from both language backgrounds were highly sensitive to dorsal mispronunciations. Combined with results from previous studies, the present outcomes are most consistent with an early, language-general bias specific to the coronal-to-labial change, which is modified by the properties of toddlers' early, language-specific lexicon.

Dialectal differences in hemispheric specialization for Japanese lexical pitch accent.

Language experience can alter perceptual abilities and the neural specialization for phonological contrasts. Here we investigated whether dialectal differences in the lexical use of pitch information lead to differences in functional lateralization for pitch processing. We measured cortical hemodynamic responses to pitch pattern changes in native speakers of Standard (Tokyo) Japanese, which has a lexical pitch accent system, and native speakers of 'accentless' dialects, which do not have any lexical tonal phenomena. While the Standard Japanese speakers showed left-dominant responses in temporal regions to pitch pattern changes within words, the accentless dialects speakers did not show such left-dominance. Pitch pattern changes within harmonic-complex tones also elicited different brain activation patterns between the two groups. These results indicate that the neural processing of pitch information differs depending on the listener's native dialect, and that listeners' linguistic experiences may further affect the processing of pitch changes even for non-linguistic sounds.

Word frequency cues word order in adults: cross-linguistic evidence.

One universal feature of human languages is the division between grammatical functors and content words. From a learnability point of view, functors might provide entry points or anchors into the syntactic structure of utterances due to their high frequency. Despite its potentially universal scope, this hypothesis has not yet been tested on typologically different languages and on populations of different ages. Here we report a corpus study and an artificial grammar learning experiment testing the anchoring hypothesis in Basque, Japanese, French, and Italian adults. We show that adults are sensitive to the distribution of functors in their native language and use them when learning new linguistic material. However, compared to infants' performance on a similar task, adults exhibit a slightly different behavior, matching the frequency distributions of their native language more closely than infants do. This finding bears on the issue of the continuity of language learning mechanisms.

What hinders child semantic computation: children's universal quantification and the development of cognitive control.

Recent studies on the acquisition of semantics have argued that knowledge of the universal quantifier is adult-like throughout development. However, there are domains where children still exhibit non-adult-like universal quantification, and arguments for the early mastery of relevant semantic knowledge do not explain what causes such non-adult-like interpretations. The present study investigates Japanese four- and five-year-old children's atypical universal quantification in light of the development of cognitive control. We hypothesized that children's still-developing cognitive control contributes to their atypical universal quantification. Using a combined eye-tracking and interpretation task together with a non-linguistic measure of cognitive control, we revealed a link between the achievement of adult-like universal quantification and the development of flexible perspective-switch. We argue that the development of cognitive control is one of the factors that contribute to children's processing of semantics.