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Successful word recognition requires that listeners attend to differences that are phonemic in the language while also remaining flexible to the variation introduced by different voices and accents. Previous work has demonstrated that American-English-learning 19-month-olds are able to balance these demands: although one-off one-feature mispronunciations typically disrupt English-learning toddlers' lexical access, they no longer do after toddlers are exposed to a novel accent in which these changes occur systematically. The flexibility to deal with different types of variation may not be the same for toddlers learning different first languages, however, as language structure shapes early phonological biases. We examined French-learning 19-month-olds' sensitivity and adaptation to a novel accent that shifted either the standard pronunciation of /a/ from [a] to [open-mid front unrounded vowel] (Experiment 1) or the standard pronunciation of /p/ from [p] to [t] (Experiment 2). In Experiment 1, French-learning toddlers recognized words with /a/ produced as [open-mid front unrounded vowel], regardless of whether they were previously exposed to an accent that contained this vowel shift or not. In Experiment 2, toddlers did not recognize words with /p/ pronounced as [t] at test unless they were first familiarized with an accent that contained this consonant shift. These findings are consistent with evidence that French-learning toddlers privilege consonants over vowels in lexical processing. Together with previous work, these results demonstrate both differences and similarities in how French- and English-learning children treat variation, in line with their language-specific phonological biases.

Within a language, there is considerable variation in the pronunciations of words owing to social factors like age, gender, nationality, and race. In the present study, we investigate whether toddlers link social and linguistic variation during word learning. In Experiment 1, 24- to 26-month-old toddlers were exposed to two talkers whose front vowels differed systematically. One talker trained them on a word-referent mapping. At test, toddlers saw the trained object and a novel object; they heard a single novel label from both talkers. Toddlers responded differently to the label as a function of talker. The following experiments demonstrate that toddlers generalize specific pronunciations across speakers of the same race (Experiment 2), but not across speakers who are simply an unfamiliar race (Experiment 3). They also generalize pronunciations based on previous affiliative behavior (Experiment 4). When affiliative behavior and race are pitted against each other, toddlers' linguistic interpretations are more influenced by affiliative behavior (Experiment 5). These experiments suggest that toddlers attend to and link social and speech variation in their environment.

Disfluencies, such as 'um' or 'uh', can cause adults to attribute uncertainty to speakers, but may also facilitate speech processing. To understand how these different functions affect children's learning, we asked whether (dis)fluency affects children's decision to select information from speakers (an explicit behavior) and their learning of specific words (an implicit behavior). In Experiment 1a, 31 3- to 4-year-olds heard two puppets provide fluent or disfluent descriptions of familiar objects. Each puppet then labeled a different novel object with the same novel word (again, fluently or disfluently). Children more frequently endorsed the object referred to by the fluent speaker. We replicated this finding with a separate group of 4-year-olds in Experiment 1b (N = 31) and a modified design. In Experiment 2, 62 3- to 4-year-olds were trained on new words, produced following a disfluency or not, and were subsequently tested on their recognition of the words. Children were equally accurate for the two types of words. These results suggest that while children may prefer information from fluent speakers, they learn words equally well regardless of fluency, at least in some contexts.

Purpose: This study examined toddlers' processing of mispronunciations based on their frequency of occurrence in child speech and the speaker who produced them. Method: One hundred twenty 22-month-olds were assigned to 1 of 4 conditions. Using the intermodal preferential looking paradigm, toddlers were shown visual displays containing 1 familiar object and 1 novel object, labeled by either a child or an adult. Familiar objects were labeled correctly or with a small mispronunciation that is either common in child speech (e.g., "waisin" for raisin) or infrequent (e.g., "rauter" for water). Results: A significant interaction of speaker and type of mispronunciation showed that, for the child speaker, toddlers treated common and infrequent mispronunciations similarly, with equivalently sized mispronunciation penalties relative to correctly pronounced labels. In contrast, for the adult speaker, toddlers showed a large penalty for common mispronunciations, but infrequent mispronunciations were treated equivalently to correct pronunciations. Conclusion: These results both reinforce and extend previous work on toddlers' processing of mispronunciations by revealing a complex interplay of speaker, type of mispronunciation, and specific contrast in toddlers' perceptions of mispronunciations.

Can children tell how different a speaker's accent is from their own? In Experiment 1 (N = 84), four- and five-year-olds heard speakers with different accents and indicated where they thought each speaker lived relative to a reference point on a map that represented their current location. Five-year-olds generally placed speakers with stronger accents (as judged by adults) at more distant locations than speakers with weaker accents. In contrast, four-year-olds did not show differences in where they placed speakers with different accents. In Experiment 2 (N = 56), the same sentences were low-pass filtered so that only prosodic information remained. This time, children judged which of five possible aliens had produced each utterance, given a reference speaker. Children of both ages showed differences in which alien they chose based on accent, and generally rated speakers with foreign accents as more different from their native accent than speakers with regional accents. Together, the findings show that preschoolers perceive accent distance, that children may be sensitive to the distinction between foreign and regional accents, and that preschoolers likely use prosody to differentiate among accents.

Language and accent strongly influence the formation of social groups. By five years of age, children already show strong social preferences for peers who speak their native language with a familiar accent (Kinzler, Shutts, DeJesus, & Spelke, 2009). However, little is known about the factors that modulate the strength and direction of children's accent-based group preferences. In three experiments, we examine the development of accent-based friendship preferences in children growing up in Toronto, one of the world's most linguistically and culturally diverse cities. We hypothesized that the speaker's type of accent and the amount of accent exposure children experienced in their everyday lives would modulate their preferences in a friend selection task. Despite literature suggesting that exposure leads to greater acceptance (Allport, 1954), we find no evidence that routine exposure to different accents leads to greater acceptance of unfamiliarly accented speakers. Children still showed strong preferences for peers who spoke with the locally dominant accent, despite growing up in a linguistically diverse community. However, children's preference for Canadian-accented in-group members was stronger when they were paired with non native (Korean-accented) speakers compared to when they were paired with regional (British-accented) speakers. We propose that children's ability to perceptually distinguish between accents may have contributed to this difference. Children showed stronger preferences for in-group members when the difference between accents was easier to perceive. Overall, our findings suggest that although the strength of accent-based social preferences can be modulated by the type of accent, these preferences still persist in the face of significant diversity in children's accent exposure.

Three experiments examined 4- to 6-year-olds' use of potential cues to geographic background. In Experiment 1 (N = 72), 4- to 5-year-olds used a speaker's foreign accent to infer that they currently live far away, but 6-year-olds did not. In Experiment 2 (N = 72), children at all ages used accent to infer where a speaker was born. In both experiments, race played some role in children's geographic inferences. Finally, in Experiment 3 (N = 48), 6-year-olds used language to infer both where a speaker was born and where they currently live. These findings reveal critical differences across development in the ways that speaker characteristics are used as inferential cues to a speaker's geographic location and history.

One of the most fundamental aspects of learning a language is determining the mappings between words and referents. An often-overlooked complication is that infants interact with multiple individuals who may not produce words in the same way. In the present study, we explored whether 10- to 12-month-olds can use talker-specific knowledge to infer the intended referents of novel labels. During exposure, infants heard two talkers whose front vowels differed; one talker trained them on a word-referent mapping. At test, infants saw the trained object and a novel object; they heard a single novel label from both talkers. When the label had a front vowel (Experiment 1), infants responded differently as a function of talker, but when it had a back vowel (Experiment 2), they did not, mapping the novel label to the novel object for both talkers. These results suggest that infants can track the phonetic properties of two simultaneously presented talkers and use information about each talker's previous productions to guide their referential interpretations.

Speech disfluencies can convey information to listeners: Adults and children predict that filled pauses (e.g., "uhh") will be followed by referents that are difficult to describe or are new to the discourse. In adults, this is driven partly by an understanding that disfluencies reflect processing difficulties. This experiment examined whether 3½-year-olds' use of disfluencies similarly involves inferences about processing difficulty. Forty children were introduced to either a knowledgeable or a forgetful speaker, who then produced fluent and disfluent utterances. Children exposed to the knowledgeable speaker looked preferentially at novel, discourse-new objects during disfluent utterances. However, children who heard the forgetful speaker did not. These results suggest that, like adults, children modify their expectations about the informativeness of disfluencies on a speaker-specific basis.

Infants begin to segment words from fluent speech during the same time period that they learn phonetic categories. Segmented words can provide a potentially useful cue for phonetic learning, yet accounts of phonetic category acquisition typically ignore the contexts in which sounds appear. We present two experiments to show that, contrary to the assumption that phonetic learning occurs in isolation, learners are sensitive to the words in which sounds appear and can use this information to constrain their interpretation of phonetic variability. Experiment 1 shows that adults use word-level information in a phonetic category learning task, assigning acoustically similar vowels to different categories more often when those sounds consistently appear in different words. Experiment 2 demonstrates that 8-month-old infants similarly pay attention to word-level information and that this information affects how they treat phonetic contrasts. These findings suggest that phonetic category learning is a rich, interactive process that takes advantage of many different types of cues that are present in the input. (Contains 1 table and 3 figures.)

Young word learners fail to discriminate phonetic contrasts in certain situations, an observation that has been used to support arguments that the nature of lexical representation and lexical processing changes over development. An alternative possibility, however, is that these failures arise naturally as a result of how word familiarity affects lexical processing. In the present work, we explored the effects of word familiarity on adults' use of phonetic detail. Participants' eye movements were monitored as they heard single-segment onset mispronunciations of words drawn from a newly learned artificial lexicon. In Experiment 1, single-feature onset mispronunciations were presented; in Experiment 2, participants heard two-feature onset mispronunciations. Word familiarity was manipulated in both experiments by presenting words with various frequencies during training. Both word familiarity and degree of mismatch affected adults' use of phonetic detail: in their looking behavior, participants did not reliably differentiate single-feature mispronunciations and correct pronunciations of low frequency words. For higher frequency words, participants differentiated both 1- and 2-feature mispronunciations from correct pronunciations. However, responses were graded such that 2-feature mispronunciations had a greater effect on looking behavior. These experiments demonstrate that the use of phonetic detail in adults, as in young children, is affected by word familiarity. Parallels between the two populations suggest continuity in the architecture underlying lexical representation and processing throughout development. (Contains 4 figures.)

The ability to infer the referential intentions of speakers is a crucial part of learning a language. Previous research has uncovered various contextual and social cues that children may use to do this. Here we provide the first evidence that children also use speech disfluencies to infer speaker intention. Disfluencies (e.g. filled pauses "uh" and "um") occur in predictable locations, such as before infrequent or discourse-new words. We conducted an eye-tracking study to investigate whether young children can make use of this distributional information in order to predict a speaker's intended referent. Our results reveal that young children (ages 2;4 to 2;8) reliably attend to speech disfluencies early in lexical development and are able to use disfluencies in online comprehension to infer speaker intention in advance of object labeling. Our results from two groups of younger children (ages 1;8 to 2;2 and 1;4 to 1;8) suggest that this ability emerges around age 2.

Word recognition is a balancing act: listeners must be sensitive to phonetic detail to avoid confusing similar words, yet, at the same time, be flexible enough to adapt to phonetically variable pronunciations, such as those produced by speakers of different dialects or by non-native speakers. Recent work has demonstrated that young toddlers are sensitive to phonetic detail during word recognition; pronunciations that deviate from the typical phonological form lead to a disruption of processing. However, it is not known whether young word learners show the flexibility that is characteristic of adult word recognition. The present study explores whether toddlers can adapt to artificial accents in which there is a vowel category shift with respect to the native language. Nineteen-month-olds heard mispronunciations of familiar words (e.g. vowels were shifted from [a] to ["ash"]: "dog" pronounced as "dag"). In test, toddlers were tolerant of mispronunciations if they had recently been exposed to the same vowel shift, but not if they had been exposed to standard pronunciations or other vowel shifts. The effects extended beyond particular items heard in exposure to words sharing the same vowels. These results indicate that, like adults, toddlers show flexibility in their interpretation of phonological detail. Moreover, they suggest that effects of top-down knowledge on the reinterpretation of phonological detail generalize across the phono-lexical system.

The brain basis of bilinguals' ability to use two languages at the same time has been a hotly debated topic. On the one hand, behavioral research has suggested that bilingual dual language use involves complex and highly principled linguistic processes. On the other hand, brain-imaging research has revealed that bilingual language switching involves neural activations in brain areas dedicated to general executive functions not specific to language processing, such as general task maintenance. Here we address the involvement of language-specific versus cognitive-general brain mechanisms for bilingual language processing. We study a unique population, "bimodal" bilinguals proficient in signed and spoken languages, and we use an innovative brain-imaging technology, functional Near-Infrared Spectroscopy (fNIRS; Hitachi ETG-4000). Like fMRI, the fNIRS technology measures hemodynamic change, but it is also advanced in permitting movement for unconstrained speech and sign production. Participant groups included (i) hearing ASL-English bilinguals, (ii) ASL monolinguals, and (iii) English monolinguals. Imaging tasks included picture naming in "Monolingual mode" (using one language at a time) and in "Bilingual mode" (using both languages either simultaneously or in rapid alternation). Behavioral results revealed that accuracy was similar among groups and conditions. By contrast, neuroimaging results revealed that bilinguals in Bilingual mode showed greater signal intensity within posterior temporal regions ("Wernicke's area") than in Monolingual mode. Significance: Bilinguals' ability to use two languages effortlessly and without confusion involves the use of language-specific posterior temporal brain regions. This research with both fNIRS and bimodal bilinguals sheds new light on the extent and variability of brain tissue that underlies language processing, and addresses the tantalizing questions of how language modality, sign and speech, impact language representation in the brain. (Contains 4 tables and 2 figures.)

In previous studies of phonological sensitivity, toddlers have failed to differentiate mispronunciations of varying severity. We provide evidence of more sophisticated phonological knowledge. Nineteen-month-olds were presented with displays consisting of one familiar and one unfamiliar object. In Experiment 1, names of familiar objects were pronounced correctly or had onset mispronunciations of one, two, or three phonetic features. Under these referential conditions, subjects demonstrated linearly graded sensitivity to the degree of mismatch. In Experiment 2, mispronunciations involved one-feature place, voice, or manner changes; in Experiment 3, subjects heard three types of two-feature onset mispronunciations. Within each of these two experiments, responses were similar to the three types of mispronunciations. Moreover, the pattern across Experiments 2 and 3 confirmed the graded sensitivity observed in Experiment 1. These results converge to suggest that 19-month-olds' representations of familiar words are quite mature and that lexical processing in toddlers (as in adults) is affected by sub-segmental detail. (Contains 4 figures and 1 table.)

We explore whether infants can learn novel phonological alternations on the basis of distributional information. In Experiment 1, two groups of 12-month-old infants were familiarized with artificial languages whose distributional properties exhibited either stop or fricative voicing alternations. At test, infants in the two exposure groups had different preferences for novel sequences involving voiced and voiceless stops and fricatives, suggesting that each group had internalized a different familiarization alternation. In Experiment 2, 8.5-month-olds exhibited the same patterns of preference. In Experiments 3 and 4, we investigated whether infants' preferences were driven solely by preferences for sequences of high transitional probability. Although 8.5-month-olds in Experiment 3 were sensitive to the relative probabilities of sequences in the familiarization stimuli, only 12-month-olds in Experiment 4 showed evidence of having grouped alternating segments into a single functional category. Taken together, these results suggest a developmental trajectory for the acquisition of phonological alternations using distributional cues in the input.

This study examines 16-month-olds' understanding of word order and inflectional properties of familiar nouns and verbs. Infants preferred grammatical sentences over ungrammatical sentences when the ungrammaticality was cued by both misplaced inflection and word order reversal of nouns and verbs. Infants were also sensitive to inflection alone as a cue to grammaticality, but not word order alone. The preference for grammatical sentence forms was also disrupted when adjacent function word cues were removed from the stimuli, and when familiar content words were replaced by nonce words. These results suggest that sensitivity to the "relationship" between functional morphemes and content words, rather than sensitivity to either independently, drives the development of early grammatical knowledge. Furthermore, infants showed some ability to generalize from familiar to nonce content word contexts. (Contains 2 tables, 3 figures and 4 footnotes.)

Infants prefer to listen to happy speech. To assess influences of speech affect on early lexical processing, 7.5- and 10.5-month-old infants were familiarized with one word spoken with happy affect and another with neutral affect and then tested on recognition of these words in fluent passages. Infants heard all passages either with happy affect or with neutral affect. Contrary to initial expectations that positive affect would facilitate word recognition, younger infants recognized familiarized words only when affect "matched" across familiarization and testing. Older infants displayed a more mature pattern of word recognition, recognizing words across variations in affect regardless of the direction of change when the task was somewhat simplified. However, younger infants continued to be limited by affective matching in the simplified task. Early processing advantages thus do not necessarily follow listening preferences. Rather, infants' early lexical representations appear to be dominated by covarying properties of experienced exemplars, whether or not these are ultimately relevant for lexical distinctions.

Infants under six months are able to discriminate native and non-native consonant contrasts equally well, but as they learn the phonological systems of their native language, this ability declines. Current explanations of this phenomenon agree that the decline in discrimination ability is linked to the formation of native-language phonemic categories. The goal of this study was to evaluate the role of input statistics in learning these categories: our hypothesis was that relative frequency is a determinant of the relative order in which categories are acquired. English-learning infants of two age groups (6.5 months and 8.5 months) were tested on their ability to discriminate non-native consonant contrasts using the Conditioned Head Turn Procedure. As predicted, older infants were worse in their performance on the more frequent coronal stop contrast than on the less frequent dorsal stop contrast. In contrast, 6.5-month-olds discriminated both contrasts equally well. An adult control group tested with an AX task also discriminated both contrasts equally. These results provide preliminary confirmation of the hypothesis that frequency plays an important role in tuning of phonological systems to properties of the native language. A simple attractor model suffices to account for these and previous results on loss of discrimination of non-native-language contrasts and suggests that the technique of measuring graded loss of multiple contrasts, in combination with observation of input frequencies, can offer a powerful method of assessing infants' phonological representations. (Contains 3 tables, 3 figures and 3 footnotes.)