The Distribution of Talker Variability Impacts Infants' Word Learning

Tonal interference in word learning? A comparison of Cantonese and French

Most languages of the world use lexical tones to contrast words. Thus, understanding how individuals process tones when learning new words is fundamental for a better understanding of the mechanisms underlying word learning. The current study asked how tonal information is integrated during word learning. We investigated whether variability in tonal information during learning can interfere with the learning of new words and whether this is language and age dependent. Cantonese- and French-learning 30-month-olds (N = 97) and Cantonese- and French-speaking adults (N = 50) were tested with an eye-tracking task on their ability to learn phonetically different pairs of novel words in two learning conditions: a 1-tone condition in which each object was named with a single label and a 3-tone condition in which each object was named with three different labels varying in tone. We predicted learning in all groups in the 1-tone condition. For the 3-tone condition, because tones are part of the phonological system of Cantonese but not of French, we expected the Cantonese groups to either fail (toddlers) or show lower performance than in the 1-tone condition (adults), whereas the French groups might show less sensitivity to this manipulation. The results show that all participants learned in the 1-tone condition and were sensitive to tone variation to some extent. Learning in the 3-tone condition was impeded in both groups of toddlers. We argue that tonal interference in word learning likely comes from the phonological level in the Cantonese groups and from the acoustic level in the French groups.

Developmental change in English-learning children's interpretations of salient pitch contours in word learning

To efficiently recognize words, children learning an intonational language like English should avoid interpreting pitch-contour variation as signaling lexical contrast, despite the relevance of pitch at other levels of structure. Thus far, the developmental time-course with which English-learning children rule out pitch as a contrastive feature has been incompletely characterized. Prior studies have tested diverse lexical contrasts and have not tested beyond 30 months. To specify the developmental trajectory over a broader age range, we extended a prior study (Quam & Swingley, 2010), in which 30-month-olds and adults disregarded pitch changes, but attended to vowel changes, in newly learned words. Using the same phonological contrasts, we tested 3- to 5-year-olds, 24-month-olds, and 18-month-olds. The older two groups were tested using the language-guided-looking method. The oldest group attended to vowels but not pitch. Surprisingly, 24-month-olds ignored not just pitch but sometimes vowels as well-conflicting with prior findings of phonological constraint at 24 months. The youngest group was tested using the Switch habituation method, half with additional phonetic variability in training. Eighteen-month-olds learned both pitch-contrasted and vowel-contrasted words, whether or not additional variability was present. Thus, native-language phonological constraint was not evidenced prior to 30 months (Quam & Swingley, 2010). We contextualize our findings within other recent work in this area.

Word Learning in Deaf Adults Who Use Cochlear Implants: The Role of Talker Variability and Attention to the Mouth

OBJECTIVES

Although cochlear implants (CIs) facilitate spoken language acquisition, many CI listeners experience difficulty learning new words. Studies have shown that highly variable stimulus input and audiovisual cues improve speech perception in CI listeners. However, less is known whether these two factors improve perception in a word learning context. Furthermore, few studies have examined how CI listeners direct their gaze to efficiently capture visual information available on a talker's face. The purpose of this study was two-fold: (1) to examine whether talker variability could improve word learning in CI listeners and (2) to examine how CI listeners direct their gaze while viewing a talker speak.

DESIGN

Eighteen adults with CIs and 10 adults with normal hearing (NH) learned eight novel word-object pairs spoken by a single talker or six different talkers (multiple talkers). The word learning task comprised of nonsense words following the phonotactic rules of English. Learning was probed using a novel talker in a two-alternative forced-choice eye gaze task. Learners' eye movements to the mouth and the target object (accuracy) were tracked over time.

RESULTS

Both groups performed near ceiling during the test phase, regardless of whether they learned from the same talker or different talkers. However, compared to listeners with NH, CI listeners directed their gaze significantly more to the talker's mouth while learning the words.

CONCLUSIONS

Unlike NH listeners who can successfully learn words without focusing on the talker's mouth, CI listeners tended to direct their gaze to the talker's mouth, which may facilitate learning. This finding is consistent with the hypothesis that CI listeners use a visual processing strategy that efficiently captures redundant audiovisual speech cues available at the mouth. Due to ceiling effects, however, it is unclear whether talker variability facilitated word learning for adult CI listeners, an issue that should be addressed in future work using more difficult listening conditions.

The effects of speaker and exemplar variability in children's cross-situational word learning

Cross-situational word learning (XSWL) - children's ability to learn words by tracking co-occurrence statistics of words and their referents over time - has been identified as a fundamental mechanism underlying lexical learning. However, it is unknown whether children can acquire new words when faced with variable input in XSWL paradigms, such as varying object exemplars and variable speakers. In the present study, we examine the separate and combined effects of exemplar and speaker variability on XSWL in typically developing English-speaking monolingual children. Results revealed that variability in speakers and exemplars did not facilitate or hinder XSWL performance. However, input that varied in both speakers and exemplars simultaneously did hinder children's word learning. Results from this work suggest that XSWL mechanisms may support categorization and generalization beyond word-object associations, but that accommodating multiple forms of variable input may incur costs. Overall, this research provides new theoretical insights into how fundamental mechanisms of word learning scale to more complex and naturalistic forms of input.

Subsegmental representation in child speech production: structured variability of stop consonant voice onset time in American English and Cantonese

Voice onset time (VOT) of aspirated stop consonants is marked by variability and systematicity in adult speech production. The present study investigated variability and systematicity of voiceless aspirated stop VOT from 161 two- to five-year-old talkers of American English and Cantonese. Overall, many aspects of child VOT productions parallel adult patterns, the analysis of which can help inform our understanding of early speech production. For instance, VOT means were comparable between children and adults, despite greater variability. Further, across children in both languages, talker-specific VOT means were strongly correlated between [th] and [kh]. This correlation may reflect a constraint of "target uniformity" that minimizes variation in the phonetic realization of a shared distinctive feature. Therefore findings suggest that target uniformity is not merely a product of a mature grammar, but may instead shape speech production representations in children as young as two years of age.

Talker variability is not always the right noise: 14 month olds struggle to learn dissimilar word-object pairs under talker variability conditions

Seminal work by Stager & Werker (1997) finds that 14-month-olds can rapidly learn two word-object pairings if the words are distinct (e.g. "neem" and "lif") but not similar (e.g. the minimal pair "bih" and "dih"). More recently, studies have found that adding talker variability during exposure to new word-object pairs lets 14-month-olds succeed on the more challenging minimal pair task, presumably due to talker variability highlighting the "relevant" consistencies between the similar words (Rost & McMurray, 2009; Galle et al., 2015; Hohle et al., 2020). It remains an open question, however, whether talker variability would be similarly useful for learning new word-object pairings when the words themselves are already distinct, or whether instead this extra variability may extinguish learning due to increased task demands. We find evidence for the latter. Namely, in our sample of 54 English-learning 14-month-olds, training infants on two word-object pairings (e.g. "neem" with a dog toy and "lof" with a kitchen tool) only led them to notice when the words and objects were switched if they were trained with single-speaker identical word tokens. When the training featured talker variability (from one or multiple talkers) infants failed to learn the pairings. We suggest that when talker variability is not necessary to highlight the invariant differences between similar words, it may actually increase task difficulty, making it harder for infants to determine what to attend to in the earliest phases of word learning.

A Protracted Developmental Trajectory for English-Learning Children's Detection of Consonant Mispronunciations in Newly Learned Words

Children are adept at learning their language's speech-sound categories, but just how these categories function in their developing lexicon has not been mapped out in detail. Here, we addressed whether, in a language-guided looking procedure, two-year-olds would respond to a mispronunciation of the voicing of the initial consonant of a newly learned word. First, to provide a baseline of mature native-speaker performance, adults were taught a new word under training conditions of low prosodic variability. In a second experiment, 24- and 30-month-olds were taught a new word under training conditions of high or low prosodic variability. Children and adults showed evidence of learning the taught word. Adults' target looking was reduced when the novel word was realized at test with a change in the voicing of the initial consonant, but children did not show any such decrement in target fixation. For both children and adults, most learners did not treat the phonologically distinct variant as a different word. Acoustic-phonetic variability during teaching did not have consistent effects. Thus, under conditions of intensive short-term training, 24- and 30-month-olds did not differentiate a newly learned word from a variant differing only in consonant voicing. High task complexity during training could explain why mispronunciation detection was weaker here than in some prior studies.

Talker variability shapes early word representations in English-learning 8-month-olds

Infants must form appropriately specific representations of how words sound and what they mean. Previous research suggests that while 8-month-olds are learning words, they struggle with recognizing different-sounding instances of words (e.g., from new talkers) and with rejecting incorrect pronunciations. We asked how adding talker variability during learning may change infants' ability to learn and recognize words. Monolingual English-learning 7- to 9-month-olds heard a single novel word paired with an object in either a "no variability," "within-talker variability," or "between-talker variability" habituation. We then tested whether infants formed appropriately specific representations by changing the talker (Experiment 1a) or mispronouncing the word (Experiment 2) and by changing the trained word or object altogether (both experiments). Talker variability influenced learning. Infants trained with no-talker variability learned the word-object link, but failed to recognize the word trained by a new talker, and were insensitive to the mispronunciation. Infants trained with talker variability dishabituated only to the new object, exhibiting difficulty forming the word-object link. Neither pattern is adult-like. Results are reported for both in-lab and Zoom participants. Implications for the role of talker variability in early word learning are discussed.

Impacts of acoustic-phonetic variability on perceptual development for spoken language: A review

This article reviews research on when acoustic-phonetic variability facilitates, inhibits, or does not impact perceptual development for spoken language, to illuminate mechanisms by which variability aids learning of language sound patterns. We first summarize structures and sources of variability. We next present proposed mechanisms to account for how and why variability impacts learning. Finally, we review effects of variability in the domains of speech-sound category and pattern learning; word-form recognition and word learning; and accent processing. Variability can be helpful, harmful, or neutral depending on the learner's age and learning objective. Irrelevant variability can facilitate children's learning, particularly for early learning of words and phonotactic rules. For speech-sound change detection and word-form recognition, children seem either unaffected or impaired by irrelevant variability. At the same time, inclusion of variability in training can aid generalization. Variability between accents may slow learning-but with the longer-term benefits of improved comprehension of multiple accents. By highlighting accent as a form of acoustic-phonetic variability and considering impacts of dialect prestige on children's learning, we hope to contribute to a better understanding of how exposure to multiple accents impacts language development and may have implications for literacy development. This article is categorized under: Linguistics > Language Acquisition Psychology > Language Psychology > Perception and Psychophysics.

Social Inference May Guide Early Lexical Learning

We incorporate social reasoning about groups of informants into a model of word learning, and show that the model accounts for infant looking behavior in tasks of both word learning and recognition. Simulation 1 models an experiment where 16-month-old infants saw familiar objects labeled either correctly or incorrectly, by either adults or audio talkers. Simulation 2 reinterprets puzzling data from the Switch task, an audiovisual habituation procedure wherein infants are tested on familiarized associations between novel objects and labels. Eight-month-olds outperform 14-month-olds on the Switch task when required to distinguish labels that are minimal pairs (e.g., “buk” and “puk”), but 14-month-olds' performance is improved by habituation stimuli featuring multiple talkers. Our modeling results support the hypothesis that beliefs about knowledgeability and group membership guide infant looking behavior in both tasks. These results show that social and linguistic development interact in non-trivial ways, and that social categorization findings in developmental psychology could have substantial implications for understanding linguistic development in realistic settings where talkers vary according to observable features correlated with social groupings, including linguistic, ethnic, and gendered groups.

Is 10 Better than 1? The Effect of Speaker Variability on Children's Cross-situational Word Learning

The current study examined the effect of speaker variability on children's cross-situational word learning (XSWL). The study also examined the role of bilingual experience and sustained attention. Forty English monolingual children and 40 Spanish-English bilingual children ages 4-7 completed a XSWL task in a Single Speaker Condition and a Multiple Speaker Condition. Results indicated that speaker variability neither facilitated nor hindered XSWL. While monolingual children outperformed bilingual children, speaker-variability effects did not fluctuate across the two language groups. Notably, exposure to multiple speakers facilitated XSWL in children with poorer sustained attention skills, suggesting that variability in the input may be especially useful to children with poorer cognitive processing abilities.

Infants' discrimination of consonant contrasts in the presence and absence of talker variability

To learn speech-sound categories, infants must identify the acoustic dimensions that differentiate categories and selectively attend to them as opposed to irrelevant dimensions. Variability on irrelevant acoustic dimensions can aid formation of robust categories in infants through adults in tasks such as word learning (e.g., Rost and McMurray, 2009) or speech-sound learning (e.g., Lively et al., 1993). At the same time, variability sometimes overwhelms learners, interfering with learning and processing. Two prior studies (Kuhl & Miller, 1982; Jusczyk, Pisoni, & Mullennix, 1992) found that irrelevant variability sometimes impaired early sound discrimination. We asked whether variability would impair or facilitate discrimination for older infants, comparing 7.5-month-old infants' discrimination of an early acquired native contrast, /p/ vs. /b/ (in the word forms /pIm/ vs. /bIm/), in Experiment 1, with an acoustically subtle, non-native contrast, /n/ vs. /ŋ/ (in /nIm/ vs. /ŋIm/), in Experiment 2. Words were spoken by one or four talkers. Infants discriminated the native but not the non-native contrast, and there were no significant effects of talker condition. We discuss implications for theories of phonological learning and avenues for future research.

Quantifying Talker Variability in North-American Infants' Daily Input

Words sound slightly different each time they are said, both by the same talker and across talkers. Rather than hurting learning, lab studies suggest that talker variability helps infants learn similar sounding words. However, very little is known about how much variability infants hear within a single talker or across talkers in naturalistic input. Here, we quantified these types of talker variability for highly frequent words spoken to 44 infants, from naturalistic recordings sampled longitudinally over a year of life (from 6 to 17 months). We used non-contrastive acoustic measurements (e.g., mean pitch, duration, harmonics-to-noise ratio) and holistic measures of sound similarity (normalized acoustic distance) to quantify acoustic variability. We find three key results. First, pitch-based variability was generally lower for infants' top talkers than across their other talkers, but overall acoustic distance is higher for tokens from the top talker versus the others. Second, the amount of acoustic variability infants heard could not be predicted from, and thus was not redundant with, other properties of the input such as the number of talkers or tokens, or proportion of speech from particular sources (e.g., women, children, electronics). Finally, we find that patterns of pitch-based acoustic variability heard in naturalistic input were similar to those found with in-lab stimuli that facilitated word learning. This large-scale quantification of talker variability in infants' everyday input sets the stage for linking naturally occurring variability "in the wild" to early word learning.

Only the right noise? Effects of phonetic and visual input variability on 14-month-olds' minimal pair word learning

Seminal work by Werker and colleagues (Stager & Werker [1997] Nature, 388, 381-382) has found that 14-month-old infants do not show evidence for learning minimal pairs in the habituation-switch paradigm. However, when multiple speakers produce the minimal pair in acoustically variable ways, infants' performance improves in comparison to a single speaker condition (Rost & McMurray [2009] Developmental Science, 12, 339-349). The current study further extends these results and assesses how different kinds of input variability affect 14-month-olds' minimal pair learning in the habituation-switch paradigm testing German learning infants. The first two experiments investigated word learning when the labels were spoken by a single speaker versus when the labels were spoken by multiple speakers. In the third experiment we studied whether non-acoustic variability, implemented by visual variability of the objects presented together with the labels, would also affect minimal pair learning. We found enhanced learning in the multiple speakers compared to the single speaker condition, confirming previous findings with English-learning infants. In contrast, visual variability of the presented objects did not support learning. These findings both confirm and better delimit the beneficial role of speech-specific variability in minimal pair learning. Finally, we review different proposals on the mechanisms via which variability confers benefits to learning and outline what may be likely principles that underlie this benefit. We highlight among these the multiplicity of acoustic cues signalling phonemic contrasts and the presence of relations among these cues. It is in these relations where we trace part of the source for the apparent paradoxical benefit of variability in learning.