Prosodic cues enhance infants' sensitivity to nonadjacent regularities

Prosody enhances learning of statistical dependencies from continuous speech streams in adults

Foreign languages sound like seamless streams of speech sounds without pauses between words and phrases. This makes it challenging for the listener to discover the underlying structure of a new language. However, all spoken languages have a melody, and changes in pitch, syllable duration and stress can provide prosodic cues about word and phrase boundaries. It is currently underspecified how adults use prosodic cues to crack the structure of a new language. Here, we investigated how pitch patterns affect the ability to learn adjacent and nonadjacent statistical dependencies from novel, artificial speech streams. In a series of eight online experiments along two studies, we presented native Finnish speakers with short, two-minute speech streams with a hidden probabilistic structure that did or did not include prosodic pitch patterns. We measured learning outcomes using a forced choice recognition task along with confidence ratings. In Study 1, we found that learning adjacent dependencies was boosted with familiar-to-listener (i.e., typical for Finnish language) prosodic pitch patterns but not with unfamiliar-to-listener or random prosodic pitch patterns. In Study 2, we found that more complex nonadjacent dependencies were only learned with the presence of familiar-to-listener prosodic patterns. Intriguingly, prosodic patterns also enabled concurrent learning of multiple adjacent and nonadjacent dependencies in speech. Moreover, they enhanced participants' confidence in remembering adjacent, but not nonadjacent, dependencies. Together, the results suggest that adults use language-background-dependent prosodic patterns to acquire novel linguistic knowledge from speech streams in a fast and efficient manner. The findings support the idea that prosody has an important role in language learning, making the underlying statistical structure of spoken languages more accessible and learnable for listeners.

Observation of cortical state-based learning in infants in a functional near-infrared spectroscopy paradigm

Significance

Learning can be context-dependent, with better outcomes under some circumstances than others. Adult functional magnetic resonance imaging studies have shown that learning outcomes vary as a function of participants' brain states-patterns of intrinsic neural activity-prior to the learning task. Whether this is also the case in young infants is currently unknown. We report the first functional near-infrared spectroscopy (fNIRS) study that shows prior brain state-dependent learning in a language task in 6.5-month-old infants. Babies whose functional connectivity was lower in the right hemisphere, but not in the left, during a 2-min period prior to the task learned better a grammatical regularity in an artificial grammar learning task.

Aim

Adult neuroimaging studies have shown that variability in brain states immediately before specific learning tasks is correlated with variability in learning outcomes. Whether the developing infant brain also shows similar state-based learning is currently unknown.

Approach

We have explored whether 6.5-month-old infants' ability to learn artificial grammar was related to their brain state during a 2-min baseline period of rest prior to the grammar task. We have asked if functional connectivity, a global metric of the cortical brain state, as measured by fNIRS, is correlated with learning a non-adjacent regularity in the artificial grammar task.

Results

We have found that the overall level of functional connectivity in the 2-min period immediately prior to the learning experience is negatively correlated with the fNIRS measure of learning in the right hemisphere but not in the left.

Conclusions

We show for the first time that the cortical state of an infant immediately prior to a learning experience determines how well that infant learns and that this can account for some of the variability in learning outcomes.

Young infants' sensitivity to precursors of vowel harmony is independent of language experience

Theories of perceptual development differ in the extent to which initial perceptual sensitivities and language experience influence infants' perception of speech. Extant research focuses largely on infants' ability to distinguish native and non-native speech sound categories. In two experiments, we investigated infants' developing perception of relationships between similar sounds, i.e., vowel harmony patterns, to inform this debate. In Experient 1, we showed that language experience is not necessary to detect vowel harmony; 4-month-olds without harmony experience can differentiate harmonic and disharmonic nonce words. We argue that this is due to a universal perceptual grouping bias, wherein similar sounds are perceived as being grouped together despite their temporal distance. Then in Experiment 2, we showed that without relevant language experience, this initial sensitivity to vowel harmony declines by 8-months as infants begin to tune into the sound patterns of their native language. We argue that our results, combined with previous findings, are best explained under perceptual attunement theories. When not reinforced by their language input, infants show a decline in their sensitivity to vowel harmony; but an initial sensitivity to relationships between similar vowels may facilitate infants' learning of vowel harmony patterns in their native language.

Lateralization of Neural Speech Discrimination at Birth Is a Predictor for Later Language Development

Newborns are able to neurally discriminate between speech and nonspeech right after birth. To date it remains unknown whether this early speech discrimination and the underlying neural language network is associated with later language development. Preterm-born children are an interesting cohort to investigate this relationship, as previous studies have shown that preterm-born neonates exhibit alterations of speech processing and have a greater risk of later language deficits. This investigation also holds clinical importance, as differences in neonatal speech discrimination and its functional networks may serve as predictors of later language outcomes. We therefore investigated neural speech discrimination using functional near-infrared spectroscopy in 92 preterm- and term-born neonates and its predictive value for language development in 45 of them. Three to five years later, preterm-born and term-born children did not significantly differ in language comprehension, sentence production, the use of morphological rules, or phonological short-term memory. In addition, the gestational age at birth was not a significant predictor of language development. Neural speech discrimination, in contrast, was strongly correlated with later phonological short-term memory. However, not the extent of speech discrimination, but rather its lateralization, was a predictor of language development. Children with less right hemisphere involvement-and therefore more left-lateralized speech discrimination at birth-showed better development of phonological short-term memory three to five years later. These findings suggest that the ability of fetuses to form memory traces is reflected by neonatal abilities to neurally discriminate speech, which in turn is a predictor for later phonological short-term memory.

Infants' reliance on rhythm to distinguish languages: A critical review

This article reviews empirical methods and findings on early language discrimination, questioning rhythm-class based hypotheses on language discrimination in infancy, as well as the assumption that early language discrimination is driven primarily (or solely) by temporal prosodic cues. The present work argues that within-rhythm class discrimination which - according to the rhythmic hypothesis - is not applicable very early in life, has not been sufficiently tested with infants under 4 months of age, that familiarity with a language is not a prerequisite for its discrimination from another rhythmically similar language, and that the temporal rhythm properties may not universally be the primary cues to language discrimination. Although rhythm taxonomy is now by many understood as outdated, some developmental literature still draws on the assumption that rhythm classification determines infants' language discrimination; other studies consider rhythm along a continuous scale and only a few account for cues to language discrimination other than temporal ones. It is proposed that studies on early language discrimination systematically test the contribution of other than temporal rhythm cues, similarly to recent work on multidimensional psychoacoustic salience in the acquisition of segmental categories.

Towards a neurodevelopmental cognitive perspective of temporal processing

The ability to organize and memorize the unfolding of events over time is a fundamental feature of cognition, which develops concurrently with the maturation of the brain. Nonetheless, how temporal processing evolves across the lifetime as well as the links with the underlying neural substrates remains unclear. Here, we intend to retrace the main developmental stages of brain structure, function, and cognition linked to the emergence of timing abilities. This neurodevelopmental perspective aims to untangle the puzzling trajectory of temporal processing aspects across the lifetime, paving the way to novel neuropsychological assessments and cognitive rehabilitation strategies.

Infant neuroscience: how to measure brain activity in the youngest minds

The functional properties of the infant brain are poorly understood. Recent advances in cognitive neuroscience are opening new avenues for measuring brain activity in human infants. These include novel uses of existing technologies such as electroencephalography (EEG) and magnetoencephalography (MEG), the availability of newer technologies including functional near-infrared spectroscopy (fNIRS) and optically pumped magnetometry (OPM), and innovative applications of functional magnetic resonance imaging (fMRI) in awake infants during cognitive tasks. In this review article we catalog these available non-invasive methods, discuss the challenges and opportunities encountered when applying them to human infants, and highlight the potential they may ultimately hold for advancing our understanding of the youngest minds.

Six-month-old infants' perception of structural regularities in speech

In order to acquire grammar, infants need to extract regularities from the linguistic input. From birth, infants can detect regularities in speech based on identity relations, and show strong neural activation to syllable sequences containing adjacent repetitions of identical syllables (e.g. ABB: mubaba). Meanwhile, newborns' neural responses to sequences of different syllables (e.g. ABC: mubage, i.e. diversity-based relations) do not differ from baseline. However, this latter ability needs to emerge during development, as most linguistic units, such as words, are composed of highly variable sequences. As infants begin to learn their first word forms at 6 months, we hypothesize that the ability to represent sequences of different syllables might become important for them at this age. Using near-infrared spectroscopy (NIRS), we measured 6-month-old infants' brain responses to repetition- and diversity-based sequences in the bilateral temporal, parietal and frontal areas. We found that 6-month-olds discriminated the repetition- and diversity-based structures in frontal and parietal regions, and exhibited equally strong activation to both grammars as compared to baseline. These results show that by 6 months of age, infants encode sequences with diversity-based structures. They thus provide the earliest evidence that prelexical infants represent difference in speech stimuli, which behavioral studies first attest at 11 months of age.