1. Introduction
While children with cochlear implants (CIs) struggle with word learning (
Houston et al., 2020) and vocabulary development (
Ingvalson et al., 2023), their phonological processing deficits often exceed their morphosyntactic challenges (
Nittrouer et al., 2018). These difficulties stem largely from the degraded speech signals provided by CI devices, especially fundamental frequency (F0) information (
Meng et al., 2021), which limits auditory input compared to that of their normal-hearing (NH) peers. The present study examines the learning of disyllabic novel words with explicit trochaic and iambic stress patterns among Mandarin-speaking preschoolers with CIs. Word-level prosodic prominence, or lexical stress, refers to the relative prominence of syllables within a word. In nontonal languages, a stressed syllable is typically perceived as higher pitched, longer and louder (
Hayes, 1995). While CI users acquiring nontonal languages remain sensitive to native stress patterns during word learning, Mandarin Chinese presents a unique typological case. In Mandarin, pitch primarily signals lexical tones rather than stress. As a result, while full-tone words lack overt stress patterns, words with a neutral tone exhibit a clear trochaic pattern (
Xu, 2023). This linguistic specificity provides a novel case for investigating whether Mandarin-speaking children with CIs show distinct preferences or difficulties in learning novel words with trochaic versus iambic stress patterns.
1.1. Effect of Language-Predominant Stress Patterns on Word Learning in Children with CIs
Typically developing infants and children acquiring nontonal languages show early sensitivity to native stress patterns, which facilitates their word learning. This sensitivity begins in utero (
Gonzalez-Gomez & Nazzi, 2012) and continues through infancy (
Mehler et al., 1988). Newborns use rhythmic information to discriminate among language types (
Nazzi et al., 1998). Consequently, word learning is shaped by phonological regularities of their native language, with prosody playing a role in early word representation (
Segal et al., 2020). Young language learners internalize the native predominant stress pattern via speech input (
Curtin, 2010;
Gerken, 1994a,
1994b;
Jusczyk et al., 1999), demonstrating language-specific biases in both word segmentation (
Curtin et al., 2005;
Johnson & Seidl, 2009;
Polka et al., 2002) and word-referent associative learning (
Graf Estes, 2014;
Broś et al., 2021). However, the hypothesis of a universal trochaic preference (
Allen & Hawkins, 1980) remains controversial. While some Hebrew-learning infants initially favor trochees despite the iambic nature of their native tongue (
Adam & Bat-El, 2009), subsequent evidence suggests that trochaic versus iambic tendencies may be methodology-dependent. Specifically, trochaic biases being more prevalent in experimental settings, whereas iambic biases in naturalistic data (
Kehoe, 2018).
Children with CIs struggle to perceive both word-level lexical stress and higher-level intonation (
Most & Peled, 2007), while their production abilities vary across languages. For instance, Hebrew-speaking children with CIs produce various stress patterns with NH-like accuracy (
Adi-Bensaid & Bat-El, 2004;
Adi-Bensaid & Most, 2009), whereas English-speaking children with CIs show significant difficulties in spontaneous speech (
Lenden & Flipsen, 2007).
Pettinato et al. (
2017) reported that during early babbling and first words production, English-learning infants with CIs employ weaker acoustic cues compared to their NH peers. Specifically, they showed overall smaller F0 and intensity distinctions, as well as reduced duration contrast between stressed and unstressed syllables.
Despite these perceptual and productive challenges, children with CIs can still access ambient lexical stress patterns and exhibit language-specific learning biases. For example, Hebrew-learning infants with CIs discriminate between trochees and iambs, favoring the predominant iambic pattern (
Segal et al., 2016). Similarly, in trochaic languages such as English, Swedish, and Dutch, children with CIs show better imitation of trochaic words (
Carter et al., 2002) or a greater tendency to omit word-initial unstressed syllables (
Sundström et al., 2018). Moreover, native Dutch-speaking adults more easily identify stress contrasts in trochaic words produced by infants with CIs (
De Clerck et al., 2019).
In summary, although children with CIs exhibit reduced stress sensitivity, they tend to follow the predominant stress patterns of their native language. Given that most existing evidence comes from nontonal languages, the present study extends this inquiry to Mandarin Chinese. We investigate whether Mandarin-speaking children with CIs can use lexical stress cues to facilitate their novel word learning.
1.2. Utilizing Novel Word Learning Tasks to Assess Word Learning Abilities in Children with CIs
Standardized assessments indicate that children with CIs generally exhibit word-learning deficits (
Geers et al., 2003). To reduce the influence of linguistic familiarity and lexical density, studies frequently employ novel word tasks (
Houston et al., 2005), where children are exposed to novel word-referent pairs and subsequently asked to identify or produce them immediately. Although children with CIs consistently underperform relative to their NH peers, they have the fundamental capacity to establish word-referent links (
Davidson et al., 2014;
Stelmachowicz et al., 2004).
However, children with CIs often find phonological production more challenging than comprehension (
Pimperton & Walker, 2018). For instance, while Hebrew-learning infants with CIs can perceptually discriminate stress patterns (
Segal et al., 2016), English-speaking CI users struggle to accurately produce them during repetition (
Dillon et al., 2004). Evidence from Greek further highlights this discrepancy. Specifically, Greek-speaking children with CIs showed stress effects during word production but not recognition (
Adamidou et al., 2023). Given that Greek is a language without a single predominant stress pattern, this asymmetry suggests distinct mechanisms underlying the recognition and production of lexical stress. That is, children with CIs may have difficulty assigning the correct stress pattern due to articulatory constraints or phonological deficits.
In summary, while infants and children with CIs possess the fundamental capacity to map novel words to referents, they generally demonstrate deficits in word learning, particularly in the accurate production of phonological forms. Like Greek, Mandarin Chinese lacks a single, overtly predominant stress pattern across its full tone vocabulary. This typological similarity raises the question of whether lexical stress influences novel word learning in Mandarin-speaking children with CIs, and whether such an effect manifests differently in word production versus recognition.
1.3. Lexical Tones, Neutral Tone and Lexical Stress in Mandarin Chinese
Mandarin Chinese is a tonal language where pitch primarily distinguishes lexical meaning through four canonical tones, i.e., T1 (high level), T2 (rising), T3 (dipping or low level), and T4 (falling) (e.g.,
ma1 “mother”,
ma2 “hemp”,
ma3 “horse”, and
ma4 “scold”, where italics indicate pinyin forms and numbers indicate tone categories in Mandarin). in addition, the system includes a neutral tone (T0), which is characterized by a shorter duration and a pitch contour determined by the preceding syllable (
Tang et al., 2018). While most Mandarin disyllabic words consist of two full-tone syllables, certain pairs contrast solely via stress patterns. For instance,
dong1 xi1 “east and west” contains two full-tone syllables, whereas
dong1 xi0 “thing” contains one full-tone syllable and one weak syllable with a neutral tone. Although such word pairs account for only 0.72% of dictionary entries (
W. Li, 1981), they represent the most overt trochaic pattern in Mandarin.
Disyllabic full-tone words are common in Mandarin Chinese, and they can fit the disyllabic foot template if possible (
Huang & Duanmu, 2013). For these words, lexical stress is perceptually subtle (
Xu, 2023), though acoustically, the second syllable often exhibits longer duration and a more complete pitch contour (
Lin et al., 1984). Previous studies have proposed that the Mandarin disyllabic foot is theoretically trochaic (
Duanmu, 2014;
Hsieh, 2021;
Wang & Feng, 2006). Evidence for this stress pattern includes constraints on trisyllabic compound formation, where adding a stressed morpheme before a disyllabic word is often restricted to avoid stress clashes (
Duanmu, 2014). Empirical support stems from coordinate compounds with irreversible syllable orders (
Hsieh, 2021) and colloquial shifts where full-tone words reduce to trochaic neutral-tone forms (
Wang & Feng, 2006).
For disyllabic words containing neutral tones, the neutral-tone syllable always occupies the right position; hence, these words clearly exhibit an overt trochaic pattern. Unlike English, where pitch is a primary correlate of stress (
Hayes, 1995), Mandarin primarily uses pitch for lexical tones. Consequently, shorter duration and lower intensity are two distinctive properties of neutral-tone syllables, whereas pitch still plays a role in neutral tone identification (
A. Li & Fan, 2015). Mandarin-speaking children with CIs face challenges in accurately producing neutral-tone words, which correspond to trochees (
Tang et al., 2019;
Yu et al., 2023). Specifically, except some familiar kinship reduplications, these children often fail to achieve adult-like acoustic realization, typically exhibiting a reduced F0 range for lexical tones and excessively long durations for neutral-tone syllables.
The unique prosodic property of Mandarin raises an interesting question: do overt stress patterns influence word learning in Mandarin-speaking children with CIs. More specifically, will these children be facilitated by a covert, theoretical trochaic pattern when learning novel words with experimentally imposed stress? Or will the acoustic challenges inherent to CI users inhibit their acquisition of trochaic patterns despite their theoretical prevalence in the native language?
1.4. The Current Study
The present study investigates the learnability of trochaic and iambic novel words in Mandarin-speaking preschoolers with CIs. Given that linguistic and perceptual skills in this population develop under conditions of early auditory deprivation, identifying their learning biases is essential for optimizing language interventions for children with severe-to-profound hearing loss. To evaluate word-referent associative learning, this study employs a novel word learning paradigm consisting of two tasks. The referent-naming task evaluates word production, examining whether children can accurately articulate the learned stress patterns. The referent-matching task assesses word recognition by requiring children to identify aurally presented novel words and match them with their corresponding referents.
Our hypotheses are grounded in the unique prosodic properties of Mandarin and the documented acoustic challenges faced by CI users. In Mandarin, overt trochaic patterns are limited to neutral-tone words, which are significantly difficult for children with CIs. We hypothesize that children with CIs will demonstrate lower overall performance and distinct learning patterns compared to their NH peers. First, we hypothesize that children with CIs would exhibit a production advantage for iambic words and face difficulty with trochaic ones. Because children with CIs tend to lengthen the second syllables within neutral-tone words, we expect this tendency to facilitate the production of iambic words, where the second syllable is inherently stressed and thus naturally longer. Conversely, we hypothesize that children with NH will show no systematic bias toward either stress pattern. Their normal auditory experience enables them to develop stable and abstract phonological representations of full tone and neutral-tone words. Their solid phonological skills should allow them to process and produce both trochaic and iambic novel words with comparable proficiency.
3. Results
All the participants were able to follow the experimental directions and provided responses. Among the 960 naming responses (16 disyllables × 2 stress patterns × 15 participants × 2 groups), 5 responses were excluded from the CI group, and 2 responses were excluded from the NH group, because they were either monosyllabic or trisyllabic. In addition, 13 responses were excluded from the CI group and 15 responses were excluded from the NH group, because they received inconsistent judgments from the three native Mandarin-speaking adults.
3.1. Quantity of Stress Pattern and Accuracy in Referent Naming
We first investigated whether there was any preference for trochees or iambs in referent naming, regardless of response accuracy.
Figure 2a presents the comparison between the two groups in the proportion of stress patterns produced. Overall, the CI group produced more iambic words than trochaic words, whereas the NH group showed no obvious preference. Statistically, the main effect of group was significant,
b = −2.24,
SE = 0.33,
z = −6.78,
p < 0.001,
OR = 0.11, 95% CI [0.05, 0.20], indicating that for the experimentally constructed trochaic items, the NH group had significantly lower odds than the CI group of producing iambic responses. The main effect of item pattern was also significant,
b = 2.45,
SE = 0.27,
z = 9.21,
p < 0.001,
OR = 11.57, 95% CI [6.99, 19.88], suggesting an overall tendency toward iambic responses. More importantly, the interaction between group and item pattern was significant,
b = 3.21,
SE = 0.48,
z = 6.64,
p < 0.001,
OR = 24.77, 95% CI [9.88, 66.18]. Follow-up simple effect analyses revealed that, for trochaic novel words, the CI group was more likely to produce iambic responses than the NH group (
p < 0.001,
OR = 9.40). For iambic novel words, the CI group was less likely to produce iambic patterns (
p = 0.017,
OR = 0.38).
For responses assessed as correct, we analyzed whether participants exhibited a production advantage for trochees or iambs.
Figure 2b presents response accuracy for each experimental condition in the naming task. The analysis of accuracy revealed a significant main effect of group,
b = 2.13,
SE = 0.37,
z = 5.78,
p < 0.001,
OR = 8.38, 95% CI [4.08, 17.23], indicating significantly higher naming accuracy in the NH group than in the CI group. A significant main effect of item pattern was also found,
b = 1.51,
SE = 0.23,
z = 6.59,
p < 0.001,
OR = 4.51, 95% CI [2.88, 7.05], suggesting that participants produced significantly more correct responses for iambic novel words than for trochaic ones. In addition, a significant group × item pattern interaction was observed,
b = −1.58,
SE = 0.37,
z = −4.24,
p < 0.001,
OR = 0.21, 95% CI [0.10, 0.43]. For the CI group, naming accuracy was significantly higher for iambic words than for trochaic words (
p < 0.001,
OR = 0.22), whereas the NH group showed no such iambic advantage (
p = 0.804,
OR = 1.08). Moreover, while the CI group performed significantly below their NH peers on trochaic words (
p < 0.001,
OR = 0.12), the two groups showed comparable accuracy for iambic words (
p = 0.150,
OR = 0.58). These results suggest that low naming accuracy in the CI group primarily occurs with trochaic items, while they nearly matched the NH group in iambic items.
In the above statistical analyses, 63 responses labeled as “equal prominence” were excluded, as they were either irrelevant to stress preference or considered incorrect. However, it is worth noting that the frequency of “equal prominence” responses varied across groups and item patterns. Among the responses produced by the CI group, 22 for trochaic novel words and 16 for iambic ones were judged as having equal prominence. Among those produced by the NH group, 9 for trochaic novel words and 16 for iambic ones were not classified as trochees or iambs.
3.2. Accuracy in Referent Matching
Figure 2c presents response accuracy for each experimental condition in the referent matching task. A significant main effect of group was found,
b = 1.72,
SE = 0.70,
z = 2.46,
p = 0.014,
OR = 5.58, 95% CI [1.44, 22.58]. However, there was no significant main effect of item pattern,
b = 1.25,
SE = 0.67,
z = 1.88,
p = 0.06,
OR = 3.50, 95% CI [0.96, 13.09], and no significant group × item pattern interaction,
b = −0.66,
SE = 0.45,
z = −1.47,
p = 0.142,
OR = 0.52, 95% CI [0.22, 1.24]. These results suggest that the CI group was less likely than the NH group to correctly match novel words with their corresponding referents. By contrast, the stress pattern of the novel words did not affect referent matching performance in either group.
The absence of a significant interaction or item effect on matching accuracy indicates that, unlike the naming task where the CI group showed a strong iambic bias, their ability to recognize these words and match them to referents was not systematically biased by the stress pattern.
3.3. F0 Range and Duration of Syllables in Referent Naming
Figure 3 shows the comparison of F0 range and duration of syllables in the two experimentally imposed stress patterns. Regarding the F0 range of trochaic novel words, the linear mixed-effects model revealed a significant main effect of syllable status,
b = −47.36,
SE = 9.96,
t(604.1) = −4.75,
p < 0.001, β = −0.271, 95% CI [−0.38, −0.16]. The non-standardized coefficient indicates that stressed syllables had a 47.36 Hz larger F0 range than unstressed syllables, and the standardized coefficient represents a medium effect of syllable status on modulation. Moreover, no significant main effect of group was found,
b = −10.84,
SE = 13.36,
t(39.8) = −0.18,
p = 0.422, β = −0.06, 95% CI [−0.21, 0.90]. Furthermore, the interaction between group and syllable status was also non-significant and characterized by a negligible effect size,
b = −0.634,
SE = 12.59,
t(604.1) = −0.05,
p = 0.96, β = −0.003, 95% CI [−0.14, 0.13]. These results collectively indicate that both NH and CI groups utilized F0 modulation as a primary cue to mark syllable stress in their novel word productions.
Regarding the F0 range of iambic novel words, only a main effect of stress status was found, b = −34.29, SE = 7.31, t(730.6) = −4.69, p < 0.001, indicating that stressed syllables had a 34.29 Hz larger F0 range than unstressed syllables. The standardized coefficient confirms a small-to-medium effect size for this acoustic contrast, β = −0.213, 95% CI [−0.30, −0.12]. However, no main effect of group was found, b = 1.87, SE = 11.66, t(40.3) = 0.16, p = 0.874, β = 0.012, 95% CI [−0.14, 0.16], nor was the group × stress status interaction, b = 8.57, SE = 10.16, t(730.6) = 0.84, p = 0.399, β = 0.047, 95% CI [−0.06, 0.16]. These negligible standardized effect sizes suggest that the contrast of F0 for iambic stress was comparable across the NH and CI groups, with no systematic differences in their phonetic realizations.
Regarding the duration of trochaic novel words, the analysis revealed a significant main effect of syllable status, b = −61.21, SE = 13.63, t(608.5) = −4.49, p < 0.001, β = −0.215, 95% CI [−0.31, −0.12], indicating that unstressed syllables were significantly shorter than stressed syllables. The main effect of group was not significant, b = −18.04, SE = 28.34, t(32.2) = −0.63, p = 0.536, β = −0.061, 95% CI [−0.26, 0.14]. More importantly, a significant interaction between group and syllable status was observed, b = −46.97, SE = 17.23, t(608.5) = −2.73, p = 0.007, β = −0.153, 95% CI [−0.26, −0.04]. This interaction indicates that the two groups differed in the magnitude of the duration contrast used to mark stress. Follow-up simple effect analyses revealed that while the two groups did not differ significantly in the duration of stressed syllables (18 ms, p = 0.536), the CI group produced significantly longer unstressed syllables than the NH group (65 ms, p = 0.031). In addition, while both groups shortened unstressed syllables relative to stressed ones, the duration contrast was substantially larger in the NH group (108.2 ms, p < 0.001) than in the CI group (61.2 ms, p < 0.001). These results suggest that although children with CIs utilize temporal cues to signal trochaic pattern, their implementation of this contrast is less robust than that of their NH peers.
Regarding the duration of iambic novel words, no main effect of group was observed, b = −46.29, SE = 24.65, t(34.9) = −1.88, p = 0.069, β = −0.144, 95% CI [−0.3, 0.01]; however, a significant effect of stress status was found, b = −76.51, SE = 11.77, t(732.7) = −6.5, p < 0.001, β = −0.239, 95% CI [−0.31, −0.17], as well as a significant group × stress status interaction, b = 47.03, SE = 16.36, t(732.7) = 2.87, p = 0.004, β = 0.129, 95% CI [0.04, 0.22]. The interaction indicates that the two groups implemented the duration contrast differently for iambic items. For stressed syllables, the CI group produced longer durations than the NH group, although this difference did not reach significance (46.3 ms, p = 0.069). For unstressed syllables, no significant group difference in duration was found (0.7 ms, p = 0.976). In addition, the duration difference between stressed and unstressed syllables was larger in the CI group (76.5 ms, p < 0.001) than in the NH group (29.5 ms, p = 0.01). These results suggest that in order to implement the iambic pattern, children with CIs tended to produce a larger contrast between stressed and unstressed syllables than their NH peers.
4. Discussion
The current study examined how Mandarin-speaking preschoolers with CIs learn novel words with overt trochaic and iambic prosodic patterns, compared to their NH peers. We hypothesized that children with CIs would show poorer word learning ability and different preferences for stress patterns when learning novel words with experimentally imposed stress patterns. The results revealed that children with CIs exhibited a distinct iambic advantage in naming tasks, both in terms of frequency and accuracy, whereas children with NH did not. In addition, although the CI group underperformed in the matching task, their recognition accuracy was unaffected by stress pattern.
The first question is why children with CIs showed an iambic advantage yet a trochaic challenge in referent naming. Our follow-up acoustic study provides a deep look into this phenomenon. Overall, stressed syllables had larger F0 ranges and longer durations than unstressed syllables. A significant between-group difference was observed in the duration of unstressed syllables within trochaic words. Specifically, children with CIs produced significantly longer unstressed syllables in these words, suggesting their difficulty in controlling temporal cues for trochees.
Two possible factors explain this difficulty in duration control. First, children with CIs struggle to shorten the second syllable in a trochee. As reported in previous studies, Mandarin-speaking preschoolers with NH often lengthen neutral-tone syllables (
Zhu & Dodd, 2000), and they tend to produce durations exceeding those of adults (
Tang et al., 2018). This lengthening pattern is even more pronounced in children with CIs (
Shen et al., 2020;
Tang et al., 2019;
Yu et al., 2023). Children learn full tone lexical words with lengthened duration. They may not yet have mastered the shortened versions of these early-learned words. Although the current stimuli were novel words, they were constructed from familiar real words. For Mandarin speakers, a familiar syllable is typically associated with a canonical tone and stored as a full tone lexical entry. Inhibiting this ingrained full realization to produce a shortened version requires fine-grained motor control, which would be difficult for children with CIs (
Adamidou et al., 2023). Second, lengthening the final syllable in an isolated word is cross-linguistically common. This phenomenon is referred to as final lengthening (
Fletcher, 2010). Thus, if a stressed syllable requires longer duration, it is easier for children to produce an isolated iambic word, where the stressed syllable occurs in final position. Compared to their NH peers, our CI participants tended to produce longer second syllables in iambic words. In contrast, producing a trochee requires either lengthening the first syllable or shortening the second syllable. This poses greater challenges to children with CIs, who thus have more difficulty producing trochaic words than iambic ones.
Notably, final lengthening typically applies to prosodic domains above the word level (
Paschen et al., 2022). According to the top-down model of prosodic development, children initially produce intonational or phonological phrases before producing syllables or feet (
Santos & Fikkert, 2008). Thus, children with CIs may have produced the novel words along with the boundary cues of higher prosodic domains. Because isolated words in daily life are themselves intonational phrases, the boundary cue of final lengthening may influence word production (
Pettinato et al., 2017;
Snow, 1994;
White, 2014). Our findings suggest that this factor influences children with CIs more than it does those with NH, who showed no naming bias toward trochaic or iambic words. Our current findings further suggest that the two groups of children may differ in prosodic processing. Children with CIs may over-generalize the lengthening patterns typically associated with higher prosodic domains and apply them to the word level, whereas children with NH are more likely to abstract the prosodic representation of novel words from various acoustic cues.
Although the “equal prominence” responses were excluded from the primary preference analysis, their occurrence is noteworthy. First, the higher frequency of these responses in the CI group, particularly for trochaic words, suggests their reduced ability to produce the duration contrast required for lexical stress. This flattened prosodic profile further reflects the challenges CI users face in phonetic implementation. Their failure to sufficiently shorten the unstressed syllable or lengthen the stressed syllable results in perceptually ambiguous stress patterns. Thus, these equal-prominence productions provide further evidence of prosodic deficits in children with CIs, specifically highlighting a failure to implement salient phonetic contrasts between syllables. Second, the stress patterns of participants’ naming responses were judged by three native Mandarin-speaking adults. Consequently, the equal-prominence judgments may be attributed to the inherent prosodic characteristics of Mandarin Chinese and the perceptual strategies of native listeners. Mandarin full-tone words lack salient acoustic and perceptual cues for word-level prominence. Our acoustic analyses revealed larger F0 ranges and longer durations of stressed syllables, highlighting the importance of F0 and duration cues in stress identification. As duration is a distinctive property of stress perception, it is possible that even if the participants attempted to implement a specific stress pattern, the acoustic cues might not have reached the threshold required for native listeners to perceive a clear stress contrast. Therefore, the equal-prominence responses stem from both the children’s difficulty in implementing robust phonetic contrasts and the listeners’ sensitivity to Mandarin’s predominantly balanced prosody.
The second question concerns why children with CIs showed no preference for either stress pattern when matching novel words with their corresponding referents. The results suggest that neither trochaic nor iambic patterns provide an advantage in forming lexical representations for Mandarin-speaking children. Although the prevalence of trochaic or iambic patterns in word learning may vary across languages and paradigms (
Kehoe, 2018), evidence from nontonal languages shows that prosody plays a role in early word representation (
Segal et al., 2020). Specifically, young language learners with NH form prosodically rich lexical representations of new words (
Curtin et al., 2005). The current study extends this research to Mandarin Chinese, i.e., from languages with salient stress cues to one where such cues are largely absent. Mandarin full-tone words are much more common than those with neutral tones (
W. Li, 1981). Although these words may theoretically exhibit a trochaic pattern (
Duanmu, 2004;
Hsieh, 2021), this pattern is difficult to perceive (
Xu, 2023). As a consequence, Mandarin-speaking children, regardless of hearing status, may not be sensitive enough to use stress cues to form lexical representations. This aligns with recent findings in Greek-speaking children with CIs, who also showed no significant difference in identifying trochaic versus iambic words (
Adamidou et al., 2023). Because Greek has no predominant stress pattern, children exhibit no lexical stress bias during referent matching. Similarly, our results support the view that when no salient stress pattern exists, no specific bias emerges in word learning. Although we experimentally imposed contrastive stress patterns, Mandarin-speaking children may not be sensitive to either pattern due to their native language background. Hence, stress pattern had no effect on word recognition.
The discrepancy between the observed iambic bias in production and its absence in recognition requires a cautious interpretation of these children’s underlying phonological representations. While children with CIs showed a clear iambic preference during naming, the lack of a corresponding effect in matching suggests that this bias may not be deeply rooted in their lexical representations. Instead, the production-only effect might stem from motoric or phonetic constraints. Specifically, children with CIs may face challenges in implementing the duration contrasts required for Mandarin trochees. Consequently, the iambic preference may reflect a distinction between phonetic performance and phonological representation. In this view, the overt output may be driven by articulatory constraints rather than by abstract phonological representations.
The finding that children with CIs had fewer correct responses than NH children suggests that they were not able to learn the novel words as well as their hearing peers. Children with profound hearing loss have deficits in word learning relative to their hearing peers (
Houston et al., 2020). In early word acquisition, infants with NH form prosodically rich lexical representations of newly encountered words. The salient acoustic properties associated with lexical stress facilitate word-referent associative learning (
Curtin, 2010). Children with CIs lack early exposure to oral speech and receive reduced-quality speech signals; hence, they have inadequate perception of acoustic cues. As a result, they have more difficulty perceiving contrastive lexical stress, face more challenges in building phonological representations of words, and demonstrate lower word learning ability.
On the other hand, our participants with CIs successfully discriminated between trochaic and iambic patterns and associated prosodic information with word meaning. This finding aligns with previous research showing that despite the degraded speech signals provided by CIs, users can still use available cues to differentiate stress patterns (
Segal et al., 2016). Therefore, CIs devices still assist children’s language development (
Sharma et al., 2020). Ultimately, our findings support the view that although children with CIs generally do not display linguistic skills equivalent to those of their NH peers, their language skills typically improve following implantation (
Nittrouer et al., 2018).
Several limitations must be acknowledged and merit consideration when interpreting our findings. First, the current experiment included only 15 participants per group due to specific clinical criteria required. This limited sample size may have reduced statistical power to detect more subtle, higher-order interactions within our mixed-effects models. Consequently, while the primary effects of stress pattern and group were clear, generalizability of these findings to the broader population of children with CIs should be interpreted with caution. Future studies with larger sample sizes are necessary to confirm these patterns.
Second, while tonal combinations were strictly controlled in constructing novel words, individual syllables were drawn from highly familiar real words. This approach may have introduced unintended lexical or phonotactic biases. Specifically, despite being presented as novel entities, these words might have triggered partial activation of familiar phonological representations in children’s mental lexicons. This possibility suggests that children’s performance might reflect reliance on existing lexical knowledge rather than formation of independent novel representations. Future studies could address this by using less frequent syllable-tone combinations or by strictly controlling for neighborhood density of constituent syllables.
Finally, regarding the absence of a significant stress effect in referent matching, while we propose that this reflects the prosodic nature of Mandarin, certain methodological factors must also be considered as alternative explanations. First, limited exposure provided during the learning phase might not have been sufficient to allow for robust encoding of prosodic contrasts. Moreover, overall task difficulty may have played a role. With an average accuracy of approximately 80% for children with NH and even lower performance for those with CIs, the task likely required significant cognitive effort for both groups to successfully encode novel word-referent associations. Under these conditions, children may prioritize mapping between the phonological label and the object over the encoding of lexical stress. Consequently, any potential processing advantage provided by a specific stress pattern may remain secondary to the primary goal of referent identification, leading to a lack of observed bias in recognition. Future research with increased exposure and more varied task difficulty levels is needed to further isolate these variables.