Brain regions and functional interactions supporting early word recognition in the face of input variability.

Perception and cognition in infants have been traditionally investigated using habituation paradigms, assuming that babies' memories in laboratory contexts are best constructed after numerous repetitions of the very same stimulus in the absence of interference. A crucial, yet open, question regards how babies deal with stimuli experienced in a fashion similar to everyday learning situations-namely, in the presence of interfering stimuli. To address this question, we used functional near-infrared spectroscopy to test 40 healthy newborns on their ability to encode words presented in concomitance with other words. The results evidenced a habituation-like hemodynamic response during encoding in the left-frontal region, which was associated with a progressive decrement of the functional connections between this region and the left-temporal, right-temporal, and right-parietal regions. In a recognition test phase, a characteristic neural signature of recognition recruited first the right-frontal region and subsequently the right-parietal ones. Connections originating from the right-temporal regions to these areas emerged when newborns listened to the familiar word in the test phase. These findings suggest a neural specialization at birth characterized by the lateralization of memory functions: the interplay between temporal and left-frontal regions during encoding and between temporo-parietal and right-frontal regions during recognition of speech sounds. Most critically, the results show that newborns are capable of retaining the sound of specific words despite hearing other stimuli during encoding. Thus, habituation designs that include various items may be as effective for studying early memory as repeated presentation of a single word.

Newborns are sensitive to multiple cues for word segmentation in continuous speech.

Before infants can learn words, they must identify those words in continuous speech. Yet, the speech signal lacks obvious boundary markers, which poses a potential problem for language acquisition (Swingley, Philos Trans R Soc Lond. Series B, Biol Sci 364(1536), 3617-3632, 2009). By the middle of the first year, infants seem to have solved this problem (Bergelson & Swingley, Proc Natl Acad Sci 109(9), 3253-3258, 2012; Jusczyk & Aslin, Cogn Psychol 29, 1-23, 1995), but it is unknown if segmentation abilities are present from birth, or if they only emerge after sufficient language exposure and/or brain maturation. Here, in two independent experiments, we looked at two cues known to be crucial for the segmentation of human speech: the computation of statistical co-occurrences between syllables and the use of the language's prosody. After a brief familiarization of about 3 min with continuous speech, using functional near-infrared spectroscopy, neonates showed differential brain responses on a recognition test to words that violated either the statistical (Experiment 1) or prosodic (Experiment 2) boundaries of the familiarization, compared to words that conformed to those boundaries. Importantly, word recognition in Experiment 2 occurred even in the absence of prosodic information at test, meaning that newborns encoded the phonological content independently of its prosody. These data indicate that humans are born with operational language processing and memory capacities and can use at least two types of cues to segment otherwise continuous speech, a key first step in language acquisition.

Statistical Speech Segmentation in Tone Languages: The Role of Lexical Tones.

Research has demonstrated distinct roles for consonants and vowels in speech processing. For example, consonants have been shown to support lexical processes, such as the segmentation of speech based on transitional probabilities (TPs), more effectively than vowels. Theory and data so far, however, have considered only non-tone languages, that is to say, languages that lack contrastive lexical tones. In the present work, we provide a first investigation of the role of consonants and vowels in statistical speech segmentation by native speakers of Cantonese, as well as assessing how tones modulate the processing of vowels. Results show that Cantonese speakers are unable to use statistical cues carried by consonants for segmentation, but they can use cues carried by vowels. This difference becomes more evident when considering tone-bearing vowels. Additional data from speakers of Russian and Mandarin suggest that the ability of Cantonese speakers to segment streams with statistical cues carried by tone-bearing vowels extends to other tone languages, but is much reduced in speakers of non-tone languages.

Language universals at birth.

The evolution of human languages is driven both by primitive biases present in the human sensorimotor systems and by cultural transmission among speakers. However, whether the design of the language faculty is further shaped by linguistic biological biases remains controversial. To address this question, we used near-infrared spectroscopy to examine whether the brain activity of neonates is sensitive to a putatively universal phonological constraint. Across languages, syllables like blif are preferred to both lbif and bdif. Newborn infants (2-5 d old) listening to these three types of syllables displayed distinct hemodynamic responses in temporal-perisylvian areas of their left hemisphere. Moreover, the oxyhemoglobin concentration changes elicited by a syllable type mirrored both the degree of its preference across languages and behavioral linguistic preferences documented experimentally in adulthood. These findings suggest that humans possess early, experience-independent, linguistic biases concerning syllable structure that shape language perception and acquisition.

On the edge of language acquisition: inherent constraints on encoding multisyllabic sequences in the neonate brain.

To understand language, humans must encode information from rapid, sequential streams of syllables - tracking their order and organizing them into words, phrases, and sentences. We used Near-Infrared Spectroscopy (NIRS) to determine whether human neonates are born with the capacity to track the positions of syllables in multisyllabic sequences. After familiarization with a six-syllable sequence, the neonate brain responded to the change (as shown by an increase in oxy-hemoglobin) when the two edge syllables switched positions but not when two middle syllables switched positions (Experiment 1), indicating that they encoded the syllables at the edges of sequences better than those in the middle. Moreover, when a 25 ms pause was inserted between the middle syllables as a segmentation cue, neonates' brains were sensitive to the change (Experiment 2), indicating that subtle cues in speech can signal a boundary, with enhanced encoding of the syllables located at the edges of that boundary. These findings suggest that neonates' brains can encode information from multisyllabic sequences and that this encoding is constrained. Moreover, subtle segmentation cues in a sequence of syllables provide a mechanism with which to accurately encode positional information from longer sequences. Tracking the order of syllables is necessary to understand language and our results suggest that the foundations for this encoding are present at birth.

Verbal positional memory in 7-month-olds.

Verbal memory is a fundamental prerequisite for language learning. This study investigated 7-month-olds' (N = 62) ability to remember the identity and order of elements in a multisyllabic word. The results indicate that infants detect changes in the order of edge syllables, or the identity of the middle syllables, but fail to encode the order of middle syllables. This suggests that the representational format of multisyllabic words is determined by core mnemonic biases, which favor accurate encoding of edges and limits the encoding of temporal order for internal segments. The studies support accounts proposing that content and order are encoded separately; in addition, the data show that this dissociation occurs early in development.

Newborn's brain activity signals the origin of word memories.

Recent research has shown that specific areas of the human brain are activated by speech from the time of birth. However, it is currently unknown whether newborns' brains also encode and remember the sounds of words when processing speech. The present study investigates the type of information that newborns retain when they hear words and the brain structures that support word-sound recognition. Forty-four healthy newborns were tested with the functional near-infrared spectroscopy method to establish their ability to memorize the sound of a word and distinguish it from a phonetically similar one, 2 min after encoding. Right frontal regions--comparable to those activated in adults during retrieval of verbal material--showed a characteristic neural signature of recognition when newborns listened to a test word that had the same vowel of a previously heard word. In contrast, a characteristic novelty response was found when a test word had different vowels than the familiar word, despite having the same consonants. These results indicate that the information carried by vowels is better recognized by newborns than the information carried by consonants. Moreover, these data suggest that right frontal areas may support the recognition of speech sequences from the very first stages of language acquisition.

Language acquisition in premature and full-term infants.

We tested healthy preterm (born near 28 +/- 2 weeks of gestational age) and full-term infants at various different ages. We compared the two populations on the development of a language acquisition landmark, namely, the ability to distinguish the native language from a rhythmically similar one. This ability is attained 4 months after birth in healthy full-term infants. We measured the induced gamma-band power associated with passive listening to (i) the infants' native language (Spanish), (ii) a rhythmically close language (Italian), and (iii) a rhythmically distant language (Japanese) as a marker of gains in language discrimination. Preterm and full-term infants were matched for neural maturation and duration of exposure to broadcast speech. We found that both full-term and preterm infants only display a response to native speech near 6 months after their term age. Neural maturation seems to constrain advances in speech discrimination at early stages of language acquisition.

Cognitive gains in 7-month-old bilingual infants.

Children exposed to bilingual input typically learn 2 languages without obvious difficulties. However, it is unclear how preverbal infants cope with the inconsistent input and how bilingualism affects early development. In 3 eye-tracking studies we show that 7-month-old infants, raised with 2 languages from birth, display improved cognitive control abilities compared with matched monolinguals. Whereas both monolinguals and bilinguals learned to respond to a speech or visual cue to anticipate a reward on one side of a screen, only bilinguals succeeded in redirecting their anticipatory looks when the cue began signaling the reward on the opposite side. Bilingual infants rapidly suppressed their looks to the first location and learned the new response. These findings show that processing representations from 2 languages leads to a domain-general enhancement of the cognitive control system well before the onset of speech.

Erratum: Disjunctive inference in preverbal infants.

[This corrects the article DOI: 10.1016/j.isci.2021.103203.].

Consonants and vowels: different roles in early language acquisition.

Language acquisition involves both acquiring a set of words (i.e. the lexicon) and learning the rules that combine them to form sentences (i.e. syntax). Here, we show that consonants are mainly involved in word processing, whereas vowels are favored for extracting and generalizing structural relations. We demonstrate that such a division of labor between consonants and vowels plays a role in language acquisition. In two very similar experimental paradigms, we show that 12-month-old infants rely more on the consonantal tier when identifying words (Experiment 1), but are better at extracting and generalizing repetition-based srtuctures over the vocalic tier (Experiment 2). These results indicate that infants are able to exploit the functional differences between consonants and vowels at an age when they start acquiring the lexicon, and suggest that basic speech categories are assigned to different learning mechanisms that sustain early language acquisition.

Speech perception and language acquisition in the first year of life.

During the first year of life, infants pass important milestones in language development. We review some of the experimental evidence concerning these milestones in the domains of speech perception, phonological development, word learning, morphosyntactic acquisition, and bilingualism, emphasizing their interactions. We discuss them in the context of their biological underpinnings, introducing the most recent advances not only in language development, but also in neighboring areas such as genetics and the comparative research on animal communication systems. We argue for a theory of language acquisition that integrates behavioral, cognitive, neural, and evolutionary considerations and proposes to unify previously opposing theoretical stances, such as statistical learning, rule-based nativist accounts, and perceptual learning theories.

The neonate brain detects speech structure.

What are the origins of the efficient language learning abilities that allow humans to acquire their mother tongue in just a few years very early in life? Although previous studies have identified different mechanisms underlying the acquisition of auditory and speech patterns in older infants and adults, the earliest sensitivities remain unexplored. To address this issue, we investigated the ability of newborns to learn simple repetition-based structures in two optical brain-imaging experiments. In the first experiment, 22 neonates listened to syllable sequences containing immediate repetitions (ABB; e.g., "mubaba," "penana"), intermixed with random control sequences (ABC; e.g., "mubage," "penaku"). We found increased responses to the repetition sequences in the temporal and left frontal areas, indicating that the newborn brain differentiated the two patterns. The repetition sequences evoked greater activation than the random sequences during the first few trials, suggesting the presence of an automatic perceptual mechanism to detect repetitions. In addition, over the subsequent trials, activation increased further in response to the repetition sequences but not in response to the random sequences, indicating that recognition of the ABB pattern was enhanced by repeated exposure. In the second experiment, in which nonadjacent repetitions (ABA; e.g., "bamuba," "napena") were contrasted with the same random controls, no discrimination was observed. These findings suggest that newborns are sensitive to certain input configurations in the auditory domain, a perceptual ability that might facilitate later language development.

Disjunctive inference in preverbal infants.

Can preverbal infants utilize logical reasoning such as disjunctive inference? This logical operation requires keeping two alternatives open (A or B), until one of them is eliminated (if not A), allowing the inference: B is true. We presented to 10-month-old infants an ambiguous situation in which a female voice was paired with two faces. Subsequently, one of the two faces was presented with the voice of a male. We measured infants' preference for the correct face when both faces and the initial voice were presented again. Infant pupillary response was measured and utilized as an indicator of cognitive load at the critical moment of disjunctive inference. We controlled for other possible explanations in three additional experiments. Our results show that 10-month-olds can correctly deploy disjunction and negation to disambiguate scenes, suggesting that disjunctive inference does not rely on linguistic constructs.

Perceptual and memory constraints on language acquisition.

A wide variety of organisms employ specialized mechanisms to cope with the demands of their environment. We suggest that the same is true for humans when acquiring artificial grammars, and at least some basic properties of natural grammars. We show that two basic mechanisms can explain many results in artificial grammar learning experiments, and different linguistic regularities ranging from stress assignment to interfaces between different components of grammar. One mechanism is sensitive to identity relations, whereas the other uses sequence edges as anchor points for extracting positional regularities. This piecemeal approach to mental computations helps to explain otherwise perplexing data, and offers a working hypothesis on how statistical and symbolic accounts of cognitive processes could be bridged.

Twelve to 24-month-olds can understand the meaning of morphological regularities in their language.

To learn a language infants must learn to link arbitrary sounds to their meaning. While words are the clearest example of this link, they are not the only component of language; morphological regularities (e.g., the plural -s suffix in English) carry meaning as well. Comprehensive theories of language acquisition must account for how infants build links between these other parts of language and their meaning. Here, we investigated the acquisition of morphology in infants learning Italian, a language with a rich inflectional morphology that marks both gender and number on both the article and final vowel of nouns. We demonstrate that infants can build these links between concepts and morphological regularities much earlier than previously thought. Italian-learning 12-18- and 24-month-olds were shown pairs of images of faces that differed either in number (1 female vs. 2 females; 1 male vs. 2 males) or gender (1 female vs. 1 male; 2 females vs. 2 males). On each trial infants were directed to look at one of the images with the morphological regularities as the only distinguishing cue. Overall, across all ages, the infants looked to the labeled image, indicating that they had at least some understanding of the morphology. While infants succeeded on both gender comparisons, they only showed evidence of understanding the feminine number distinction. These results indicate that in the early stages of language acquisition, infants are able to identify recurring morphemes and to map those morphological regularities to the concepts that they mark in the language. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Neural Signal to Violations of Abstract Rules Using Speech-Like Stimuli.

As the evidence of predictive processes playing a role in a wide variety of cognitive domains increases, the brain as a predictive machine becomes a central idea in neuroscience. In auditory processing, a considerable amount of progress has been made using variations of the Oddball design, but most of the existing work seems restricted to predictions based on physical features or conditional rules linking successive stimuli. To characterize the predictive capacity of the brain to abstract rules, we present here two experiments that use speech-like stimuli to overcome limitations and avoid common confounds. Pseudowords were presented in isolation, intermixed with infrequent deviants that contained unexpected phoneme sequences. As hypothesized, the occurrence of unexpected sequences of phonemes reliably elicited an early prediction error signal. These prediction error signals do not seemed to be modulated by attentional manipulations due to different task instructions, suggesting that the predictions are deployed even when the task at hand does not volitionally involve error detection. In contrast, the amount of syllables congruent with a standard pseudoword presented before the point of deviance exerted a strong modulation. Prediction error's amplitude doubled when two congruent syllables were presented instead of one, despite keeping local transitional probabilities constant. This suggests that auditory predictions can be built integrating information beyond the immediate past. In sum, the results presented here further contribute to the understanding of the predictive capabilities of the human auditory system when facing complex stimuli and abstract rules.

Congenital amusia: a disorder of fine-grained pitch discrimination.

We report the first documented case of congenital amusia. This disorder refers to a musical disability that cannot be explained by prior brain lesion, hearing loss, cognitive deficits, socioaffective disturbance, or lack of environmental stimulation. This musical impairment is diagnosed in a middle-aged woman, hereafter referred to as Monica, who lacks most basic musical abilities, including melodic discrimination and recognition, despite normal audiometry and above-average intellectual, memory, and language skills. The results of psychophysical tests show that Monica has severe difficulties with detecting pitch changes. The data suggest that music-processing difficulties may result from problems in fine-grained discrimination of pitch, much in the same way as many language-processing difficulties arise from deficiencies in auditory temporal resolution.

Bootstrapping word order in prelexical infants: a Japanese-Italian cross-linguistic study.

Learning word order is one of the earliest feats infants accomplish during language acquisition [Brown, R. (1973). A first language: The early stages, Cambridge, MA: Harvard University Press.]. Two theories have been proposed to account for this fact. Constructivist/lexicalist theories [Tomasello, M. (2000). Do young children have adult syntactic competence? Cognition, 74(3), 209-253.] argue that word order is learned separately for each lexical item or construction. Generativist theories [Chomsky, N. (1995). The Minimalist Program. Cambridge, MA: MIT Press.], on the other hand, claim that word order is an abstract and general property, determined from the input independently of individual words. Here, we show that eight-month-old Japanese and Italian infants have opposite order preferences in an artificial grammar experiment, mirroring the opposite word orders of their respective native languages. This suggests that infants possess some representation of word order prelexically, arguing for the generativist view. We propose a frequency-based bootstrapping mechanism to account for our results, arguing that infants might build this representation by tracking the order of functors and content words, identified through their different frequency distributions. We investigate frequency and word order patterns in infant-directed Japanese and Italian corpora to support this claim.

Do Humans Really Learn A(n) B(n) Artificial Grammars From Exemplars?

An important topic in the evolution of language is the kinds of grammars that can be computed by humans and other animals. Fitch and Hauser (F&H; 2004) approached this question by assessing the ability of different species to learn 2 grammars, (AB)(n) and A(n) B(n) . A(n) B(n) was taken to indicate a phrase structure grammar, eliciting a center-embedded pattern. (AB)(n) indicates a grammar whose strings entail only local relations between the categories of constituents. F&H's data suggest that humans, but not tamarin monkeys, learn an A(n) B(n) grammar, whereas both learn a simpler (AB)(n) grammar (Fitch & Hauser, 2004). In their experiments, the A constituents were syllables pronounced by a female voice, whereas the B constituents were syllables pronounced by a male voice. This study proposes that what characterizes the A(n) B(n) exemplars is the distributional regularities of the syllables pronounced by either a male or a female rather than the underlying, more abstract patterns. This article replicates F&H's data and reports new controls using either categories similar to those in F&H or less salient ones. This article shows that distributional regularities explain the data better than grammar learning. Indeed, when familiarized with A(n) B(n) exemplars, participants failed to discriminate A(3) B(2) and A(2) B(3) from A(n) B(n) items, missing the crucial feature that the number of As must equal the number of Bs. Therefore, contrary to F&H, this study concludes that no syntactic rules implementing embedded nonadjacent dependencies were learned in these experiments. The difference between human linguistic abilities and the putative precursors in monkeys deserves further exploration.