The present study investigates Korean mothers’ use of sound symbolism, in particular expressive lengthening and ideophones, in their speech directed to their children. Specifically, we explore whether the frequency and acoustic saliency of sound symbolic words are modulated by the maturity of children’s linguistic ability. A total of 36 infant-mother dyads, 12 each belonging to the three groups of preverbal (M = 8-month-old), early speech (M = 13-month-old), and multiword (M = 27-month-old) stage, were recorded in a 40-min free-play session. The results were consistent with the findings in previous research that the ratio of sound symbolic words in mothers’ speech decreases with child age and that they are acoustically more salient than conventional words in duration and pitch measures. We additionally found that mothers weaken the prominence for ideophones for older children in mean pitch, suggesting that such prominence of these iconic words might bootstrap infants’ word learning especially when they are younger. Interestingly, however, we found that mothers maintain the acoustic saliency of expressive lengthening consistently across children’s ages in all acoustic measures. There is some indication that children at age 2 are not likely to have mastered the fine details of scalar properties in certain words. Thus, it could be that they still benefit from the enhanced prosody of expressive lengthening in learning the semantic attributes of scalar adjectives, and, accordingly, mothers continue to provide redundant acoustic cues longer for expressive lengthening than ideophones.

We describe a corpus of speech taking place between 30 Korean mother–child pairs, divided in three groups of Prelexical (M = 0;08), Early-Lexical (M = 1;02), and Advanced-Lexical (M = 2;03). In addition to the child-directed speech (CDS), this corpus includes two different formalities of adult-directed speech (ADS), i.e., family-directed ADS (ADS_Fam) and experimenter-directed ADS (ADS_Exp). Our analysis of the MLU in CDS, family-, and experimenter-directed ADS found significant differences between CDS and ADS_Fam, and between ADS_Fam and ADS_Exp, but not between CDS and ADS_Exp. Our finding suggests that researchers should pay more attention to controlling the level of formality in CDS and ADS when comparing the two registers for their speech characteristics. The corpus was transcribed in the CHAT format of the CHILDES system, so users can easily extract data related to verbal behavior in the mother–child interaction using the CLAN program of CHILDES.

The relative ease of children’s learning of nouns vs. verbs can be explained by the characteristics of linguistic input. In Korean, syntactic structures contain parameters adversarial for learning nouns such as the SOV word-order, in which noun appears utterance-medially, and frequent elision of noun. Nevertheless, Korean children readily learn nouns and even show a noun-bias in production. We investigate two strategies Korean mothers adopt to aid children’s noun learning: adapting the default word-order to place nouns in the utterance-final position, and presenting the nouns in repetition. In Study 1, we examined the distribution of nouns in Korean and English child-directed speech (CDS) and found that Korean mothers scramble the word-order to [(S)VO] or repeat the noun at the end of the utterance [(S)OV, O], which we term tag-repetition, especially when the children were younger. These patterns were rarely found in English-speaking mothers’ speech. They also presented nouns in isolation with a higher rate than English, particularly to youngest children. To test whether the Korean mothers’ adaptation of word-order and repetition is specific to CDS, we compared the rate of word-order adaptation and lexical repetition of nouns in Korean CDS and adult-directed speech (ADS). The results showed that in spontaneous speech, Korean mothers place nouns on the edges and employed tag repetition more frequently in CDS than in ADS. The findings suggest that mothers might have a tacit knowledge of the importance of utterance-final position and syntactic constraints, and adapt their language to address the language-specific constraints in the input.

Speakers of North American English are known to use a variety of tap/flap articulations depending on phonetic context (Derrick and Gick, 2011); it is also known that NAE taps/flaps are sometimes associated with a greatly lowered F4 frequency (Warner and Tucker, 2017). It has been less clear whether only certain articulatory variants show this acoustic effect. Since retroflex stops are also associated with lowered F4 (Blumstein and Stevens, 1975), we predict that flap retroflexion is associated with lowered F4. To test this prediction, synchronized ultrasound and audio recordings were made of words containing /t, d/ in a variety of contexts known to give rise to tap/flap variants. Based on visual inspection of ultrasound videos, these were coded as one of four articulatory variants (low tap, high tap, up flap, down flap: Derrick and Gick, 2011); formant frequencies were extracted from the audio at several timepoints relative to the tap/flap. Preliminary results from one speaker support the hypothesis: high taps and down flaps (variants with initial retroflexion) show an F4 drop into the consonant, while high taps and up flaps (variants with final retroflexion) show an F4 rise out of the consonant.