Laura E. Hahn

Background: Asymmetric hearing loss (HL) is a common pediatric condition, characterized by differences in HL severity between both ears. Anamnestic and audiologic profiles of affected children are sparse, hindering development of evidence-based clinical guidelines. Methods: Clinical characteristics for children with bi- and unilateral asymmetric HL were retrospectively obtained from a register of children with permanent HL in Germany. Cohorts were stratified by laterality (uni-/bilateral) and presence of comorbidities (with/without). Between-group differences were assessed using absolute standardized mean differences. Results: Here we show, across uni- and bilateral groups, family history of HL is reported for approximately 25% and comorbidities for 40%-50% of children. Children with bilateral HL have a higher proportion of pre-/perinatal risk factors (e.g., hypoxia, artificial ventilation) than children with unilateral HL. Hereditary HL is more common in children with bilateral HL, whereas unexplained causes of HL is more frequent in unilateral cases. Sensorineural HL is predominant across groups; conductive or combined HL occurs more often in children with unilateral HL and comorbidities. Sloping and flat audiogram configurations are common across groups, though many children also exhibit other shapes. Notably, 60% of children with bilateral HL present different audiogram configurations in their left and right ears. Conclusion: Children with asymmetric HL represent a heterogeneous population with diverse clinical characteristics. This study highlights the need for comprehensive audiologic examination and tailored technical intervention. Bilateral asymmetries may pose greater clinical challenges compared to unilateral cases, due to higher incidence of comorbidities and risk factors as well as the high incidence of inter-aural differences in audiogram configurations.

In the current chapter, we address infants’ language-acquisition challenges in extracting regularities (such as phonemes, words and phrases) from the variable acoustic input of the continuous signal of both speech and song. We review the (musical) characteristics of infant-directed speech and song, including pitch characteristics, speech rate, boundary marking, rhythm and repetition, and the evidence for potential benefits of these characteristics for language development. Compared to adult-directed speech, infant-directed speech is generally slower and higher pitched, contains many repetitions and shows stronger rhythmic regularity, combined with higher pitch variability and enhanced boundary marking. Songs are highly captivating for infants, and song exposure is positively associated with infants’ language development. Infant-directed song is inherently rhythmical, with pitch being bound to the melody, resulting in a predictable temporal and melodic structure. Benefits for language acquisition might arise because musical characteristics in infant-directed communication help the infant to learn where, how, and when to focus their attention. This is essential for identifying and memorizing linguistic units and structure at different timescales. While rhythmic regularity and repetition increase predictability and might set up a scaffold facilitating (neural) processing, variability in both tempo and pitch could draw attention to specific parts within this scaffold. This way, musical characteristics in infant-directed speech and song might help infants to discover meaningful units and structure in the input, facilitating further language learning.

Language outcomes of children with hearing loss remain heterogeneous despite recent advances in treatment and intervention. Consonants with high frequency, in particular, continue to pose challenges to affected children’s speech perception and production. In this review, we evaluate findings of how enriched child-directed speech and song might function as a form of early family-centered intervention to remedy the effects of hearing loss on consonant acquisition already during infancy. First, we review the developmental trajectory of consonant acquisition and how it is impeded by permanent pediatric hearing loss. Second, we assess how phonetic-prosodic and lexico-structural features of caregiver speech and song could facilitate acquisition of consonants in the high frequency range. Finally, recommendations for clinical routines and further research are expressed.

Neural tracking of the low frequency amplitude envelope of speech is considered a driving factor for language processing and development. This study explored to what extent infants’ neural tracking of spoken nursery rhymes is modulated by top-down and bottom-up processing factors, namely vocabulary size and regular speech rhythm. In addition, infants’ ERPs for rhyming and non-rhyming pseudowords at the end of each nursery rhyme line were compared for metered versus non-metered nursery rhymes. Dutch 10.5-month-old infants listened to naturalistic rhyming and non-rhyming nursery rhymes that either had a salient 1.5 Hz stress rhythm (metered nursery rhymes) or deviated in one syllable to disrupt the rhythmic pattern (non-metered nursery rhymes). Neural tracking was found for the stress rate as well as for the syllable rate of the nursery rhymes, for both metered and non-metered nursery rhymes. At the syllable rate, neural tracking was higher for non-metered nursery rhymes. Improved syllable tracking of non-metered nursery rhymes might reflect infants’ maturing auditory processing abilities in dealing with non-isochronous everyday speech. Syllable rate tracking was negatively correlated with concurrent vocabulary, but positively correlated with future vocabulary, suggesting a developmental change in infants’ auditory processing focus as their lexicons increase. ERPs for rhyming line-final pseudowords in the nursery rhymes resembled previous research for rhyming songs (Hahn et al., 2021). Yet their relationship with speech rhythm, neural tracking and lexical development raise questions for further research.

Rhyme perception is an important predictor for future literacy. Assessing rhyme abilities, however, commonly requires children to make explicit rhyme judgements on single words. Here we explored whether infants already implicitly process rhymes in natural rhyming contexts (child songs) and whether this response correlates with later vocabulary size. In a passive listening ERP study, 10.5 month-old Dutch infants were exposed to rhyming and non-rhyming child songs. Two types of rhyme effects were analysed: (1) ERPs elicited by the first rhyme occurring in each song (rhyme sensitivity) and (2) ERPs elicited by rhymes repeating after the first rhyme in each song (rhyme repetition). Only for the latter a tentative negativity for rhymes from 0 to 200 ms after the onset of the rhyme word was found. This rhyme repetition effect correlated with productive vocabulary at 18 months-old, but not with any other vocabulary measure (perception at 10.5 or 18 months-old). While awaiting future replication, the study indicates precursors of phonological awareness already during infancy and with ecologically valid linguistic stimuli.

Infants exploit acoustic boundaries to perceptually organize phrases in speech. This prosodic parsing ability is well‐attested and is a cornerstone to the development of speech perception and grammar. However, infants also receive linguistic input in child songs. This study provides evidence that infants parse songs into meaningful phrasal units and replicates previous research for speech. Six‐month‐old Dutch infants (n = 80) were tested in the song or speech modality in the head‐turn preference procedure. First, infants were familiarized to two versions of the same word sequence: One version represented a well‐formed unit, and the other contained a phrase boundary halfway through. At test, infants were presented two passages, each containing one version of the familiarized sequence. The results for speech replicated the previously observed preference for the passage containing the well‐formed sequence, but only in a more fine‐grained analysis. The preference for well‐formed phrases was also observed in the song modality, indicating that infants recognize phrase structure in song. There were acoustic differences between stimuli of the current and previous studies, suggesting that infants are flexible in their processing of boundary cues while also providing a possible explanation for differences in effect sizes.

Children’s songs are a great source for linguistic learning. Here we explore whether children can acquire novel words in a second language by playing a game featuring children’s songs in a playhouse. The playhouse is designed by the Noplica foundation (www.noplica.nl) to advance language learning through unsupervised play. We present data from three experiments that serve to scientifically prove the functionality of one game of the playhouse: the Energy Center. For this game, children move three hand-bikes mounted on a panel within the playhouse. Once the children cycle, a song starts playing that is accompanied by musical instruments. In our experiments, children executed a picture selection task to evaluate whether they acquired new vocabulary from the songs presented during cycling. Two of our experiments were run in the field, one at a Dutch and one at an Indian preschool. The third experiment features data from a more controlled laboratory setting. Our results partly confirm that the Energy Center is a successful means to support vocabulary acquisition in a second language. More research with larger sample sizes and longer access to the Energy Center is needed to evaluate the overall functionality of the game. Based on informal observations at our test sites, however, we are certain that children do pick up linguistic content from the songs during play, as many of the children repeat words and phrases from the songs they heard. We will pick up upon these promising observations in future studies.