Infants’ perception of repetition-based regularities in speech: a look from the perspective of the same/different distinction

The developmental cognitive mechanism of learning algebraic rules from the dual-process theory perspective

Rule learning is an important ability that enables human beings to adapt to nature and develop civilizations. There have been many discussions on the mechanism and characteristics of algebraic rule learning, but there are still controversies due to the lack of theoretical guidance. Based on the dual-process theory, this study discussed the following arguments for algebraic rule learning across human and animal studies: whether algebraic rule learning is simply Type 1 processing, whether algebraic rule learning is a domain-general ability, whether algebraic rule learning is shared by humans and animals, and whether an algebraic rule is learned consciously. Moreover, we propose that algebraic rule learning is possibly a cognitive process that combines both Type 1 and Type 2 processing. Further exploration is required to establish the essence and neural basis of algebraic rule learning.

Brain responses to repetition-based rule-learning do not exhibit sex differences: an aggregated analysis of infant fNIRS studies

Studies have repeatedly shown sex differences in some areas of language development, typically with an advantage for female over male children. However, the tested samples are typically small and the effects do not always replicate. Here, we used a meta-analytic approach to address this issue in a larger sample, combining seven fNIRS studies on the neural correlates of repetition- and non-repetition-based rule learning in newborns and 6-month-old infants. The ability to extract structural regularities from the speech input is fundamental for language development, it is therefore highly relevant to understand whether this ability shows sex differences. The meta-analysis tested the effect of Sex, as well as of other moderators on infants' hemodynamic responses to repetition-based (e.g. ABB: "mubaba") and non-repetition-based (e.g. ABC: "mubage") sequences in both anatomically and functionally defined regions of interests. Our analyses did not reveal any sex differences at birth or at 6 months, suggesting that the ability to encode these regularities is robust across sexes. Interestingly, the meta-analysis revealed other moderator effects. Thus in newborns, we found a greater involvement of the bilateral temporal areas compared to the frontal areas for both repetition and non-repetition sequences. Further, non-repetition sequences elicited greater responses in 6-month-olds than in newborns, especially in the bilateral frontal areas. When analyzing functional clusters of HbR timetraces, we found that a larger right-left asymmetry for newborn boys in brain responses compared to girls, which may be interpreted in terms of a larger right-left asymmetry in cerebral blood flow in boys than in girls early in life. We conclude that extracting repetition-based regularities from speech is a robust ability with a well-defined neural substrate present from birth and it does not exhibit sex differences.

The neonate brain's sensitivity to repetition-based structure: Specific to speech?

Newborns are able to extract and learn repetition-based regularities from the speech input, that is, they show greater brain activation in the bilateral temporal and left inferior frontal regions to trisyllabic pseudowords of the form AAB (e.g., "babamu") than to random ABC sequences (e.g., "bamuge"). Whether this ability is specific to speech or also applies to other auditory stimuli remains unexplored. To investigate this, we tested whether newborns are sensitive to regularities in musical tones. Neonates listened to AAB and ABC tones sequences, while their brain activity was recorded using functional Near-Infrared Spectroscopy (fNIRS). The paradigm, the frequency of occurrence and the distribution of the tones were identical to those of the syllables used in previous studies with speech. We observed a greater inverted (negative) hemodynamic response to AAB than to ABC sequences in the bilateral temporal and fronto-parietal areas. This inverted response was caused by a decrease in response amplitude, attributed to habituation, over the course of the experiment in the left fronto-temporal region for the ABC condition and in the right fronto-temporal region for both conditions. These findings show that newborns' ability to discriminate AAB from ABC sequences is not specific to speech. However, the neural response to musical tones and spoken language is markedly different. Tones gave rise to habituation, whereas speech was shown to trigger increasing responses over the time course of the study. Relatedly, the repetition regularity gave rise to an inverted hemodynamic response when carried by tones, while it was canonical for speech. Thus, newborns' ability to detect repetition is not speech-specific, but it engages distinct brain mechanisms for speech and music. RESEARCH HIGHLIGHTS: The ability of newborns' to detect repetition-based regularities is not specific to speech, but also extends to other auditory modalities. The brain mechanisms underlying speech and music processing are markedly different.

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.

Reproducibility of infant fNIRS studies: a meta-analytic approach

SIGNIFICANCE

Concerns about the reproducibility of experimental findings have recently emerged in many disciplines, from psychology to medicine and neuroscience. As NIRS is a relatively recent brain imaging technique, the question of reproducibility has not yet been systematically addressed.

AIM

The current study seeks to test the replicability of effects observed in NIRS experiments assessing young infants' rule-learning ability.

APPROACH

We conducted meta-analyses and mixed-effects modeling-based inferential statistics to determine whether effect sizes were replicable and comparable in a sample of 23 NIRS studies investigating infants' abilities to process repetition- and diversity-based regularities in linguistic and nonlinguistic auditory and visual sequences. Additionally, we tested whether effect sizes were modulated by different factors such as the age of participants or the laboratory. We obtained NIRS data from 12 published and 11 unpublished studies. The 23 studies involved a total of 487 infants, aged between 0 and 9 months, tested in four different countries (Canada, France, Italy, and USA).

RESULTS

Our most important finding is that study and laboratory were never significant moderators of variation in effect sizes, indicating that results replicated reliably across the different studies and labs included in the sample. We observed small-to-moderate effect sizes, similar to effect sizes found with other neuroimaging and behavioral techniques in the developmental literature. In line with existing findings, effect sizes were modulated by the participants' age and differed across the different regularities tested, with repetition-based regularities giving rise to the strongest effects; in particular, the overall magnitude of this effect in the left temporal region was 0.27 when analyzing the entire dataset.

CONCLUSIONS

Meta-analysis is a useful tool for assessing replicability and cross-study variability. Here, we have shown that infant NIRS studies in the language domain replicate robustly across various NIRS machines, testing sites, and developmental populations.

Abstract representations of small sets in newborns

From the very first days of life, newborns are not tied to represent narrow, modality- and object-specific aspects of their environment. Rather, they sometimes react to abstract properties shared by stimuli of very different nature, such as approximate numerosity or magnitude. As of now, however, there is no evidence that newborns possess abstract representations that apply to small sets: in particular, while newborns can match large approximate numerosities across senses, this ability does not extend to small numerosities. In two experiments, we presented newborn infants (N = 64, age 17 to 98 h) with patterned sets AB or ABB simultaneously in the auditory and visual modalities. Auditory patterns were presented as periodic sequences of sounds (AB: triangle-drum-triangle-drum-triangle-drum …; ABB: triangle-drum-drum-triangle-drum-drum-triangle-drum-drum …), and visual patterns as arrays of 2 or 3 shapes (AB: circle-diamond; ABB: circle-diamond-diamond). In both experiments, we found that participants reacted and looked longer when the patterns matched across the auditory and visual modalities – provided that the first stimulus they received was congruent. These findings uncover the existence of yet another type of abstract representations at birth, applying to small sets. As such, they bolster the hypothesis that newborns are endowed with the capacity to represent their environment in broad strokes, in terms of its most abstract properties. This capacity for abstraction could later serve as a scaffold for infants to learn about the particular entities surrounding them.

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Newborns were presented with auditory and visual patterns (AB vs. ABB).

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Participants reacted when the patterns presented were congruent across modalities.

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Newborns possess abstract representations applying to small sets.

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These representations may encode numerosity and/or repetitions.