Limited evidence of test-retest reliability in infant-directed speech preference in a large preregistered infant experiment.

Test-retest reliability-establishing that measurements remain consistent across multiple testing sessions-is critical to measuring, understanding, and predicting individual differences in infant language development. However, previous attempts to establish measurement reliability in infant speech perception tasks are limited, and reliability of frequently used infant measures is largely unknown. The current study investigated the test-retest reliability of infants' preference for infant-directed speech over adult-directed speech in a large sample (N = 158) in the context of the ManyBabies1 collaborative research project. Labs were asked to bring in participating infants for a second appointment retesting infants on their preference for infant-directed speech. This approach allowed us to estimate test-retest reliability across three different methods used to investigate preferential listening in infancy: the head-turn preference procedure, central fixation, and eye-tracking. Overall, we found no consistent evidence of test-retest reliability in measures of infants' speech preference (overall r = 0.09, 95% CI [-0.06,0.25]). While increasing the number of trials that infants needed to contribute for inclusion in the analysis revealed a numeric growth in test-retest reliability, it also considerably reduced the study's effective sample size. Therefore, future research on infant development should take into account that not all experimental measures may be appropriate for assessing individual differences between infants. RESEARCH HIGHLIGHTS: We assessed test-retest reliability of infants' preference for infant-directed over adult-directed speech in a large pre-registered sample (N = 158). There was no consistent evidence of test-retest reliability in measures of infants' speech preference. Applying stricter criteria for the inclusion of participants may lead to higher test-retest reliability, but at the cost of substantial decreases in sample size. Developmental research relying on stable individual differences should consider the underlying reliability of its measures.

Prenatal experience with language shapes the brain.

Human infants acquire language with notable ease compared to adults, but the neural basis of their remarkable brain plasticity for language remains little understood. Applying a scaling analysis of neural oscillations to address this question, we show that newborns' electrophysiological activity exhibits increased long-range temporal correlations after stimulation with speech, particularly in the prenatally heard language, indicating the early emergence of brain specialization for the native language.

The role of language in building abstract, generalized conceptual representations of one- and two-place predicates: A comparison between adults and infants.

Theories of relations between language and conceptual development benefit from empirical evidence for concepts available in infancy, but such evidence is comparatively scarce. Here, we examine early representations of specific concepts, namely, sets of dynamic events corresponding either to predicates involving two variables with a reversible, asymmetric relation between them (such as the set of all events that correspond to a linguistic phrase like "a dog is pushing a car,") or to comparatively simpler, one-variable predicates (such as the set of events corresponding to a phrase like "a dog is jumping."). We develop a non-linguistic, anticipatory eye-tracking task that can be administered to both infants and adults, and we use this task to gather evidence for the formation and use of such one-and two-place-predicate classes (which we refer to as event sortals) in 12-24-mo-old infants, and in adults with and without concurrent verbal prose shadowing. Using visually similar stimuli for both the simpler (one-place) and the more complex (reversible, asymmetric, two-place) concepts, we find that infants only show evidence for forming and generalizing one-place event sortals, and, while adults succeed with both kinds in the absence of verbal shadowing, shadowing hampers their ability to form and use the asymmetric two-place event sortals. In a subsequent experiment with adults, we find that if the shadowing material is grammatically impoverished, adults now succeed in forming and using both one- and two-place event sortals. We discuss implications of these results for theories of concept acquisition, and the role of language in this process.

A New Proposal for Phoneme Acquisition: Computing Speaker-Specific Distribution.

Speech is an acoustically variable signal, and one of the sources of this variation is the presence of multiple speakers. Empirical evidence has suggested that adult listeners possess remarkably sensitive (and systematic) abilities to process speech signals, despite speaker variability. It includes not only a sensitivity to speaker-specific variation, but also an ability to utilize speaker variation with other sources of information for further processing. Recently, many studies also showed that young children seem to possess a similar capacity. This suggests continuity in the processing of speaker-dependent speech variability, and suggests that this ability could also be important for infants learning their native language. In the present paper, we review evidence for speaker variability and speech processing in adults, and speaker variability and speech processing in young children, with an emphasis on how they make use of speaker-specific information in word learning situations. Finally, we will build on these findings to make a novel proposal for the use of speaker-specific information processing in phoneme learning in infancy.

Emotion and decision-making: Induced mood influences IGT scores and deck selection strategies.

The somatic marker hypothesis (SMH) represents a rich neuropsychological framework to study emotion-based decision-making. It originates from early brain lesion studies using the Iowa Gambling Task (IGT), which showed that adaptive decision-making relies on intact ventromedial prefrontal cortex for the integration of so-called "hot" affective signals and rational "cold" perceptual cognitive computations. Subsequent studies over the past 20 years have provided converging evidence for the reliability and validity of the IGT in assessing decision-making in both healthy and clinical samples, although some discrepancies remain. In healthy individuals, it has been shown that differences in emotional states prior to taking the IGT result in different outcomes, thus potentially accounting for some of the variation within this group. However, the precise role of such transient modulations of emotional states remains unclear. In this study we sought to examine the role of specific induced moods under carefully controlled conditions. Accordingly, we randomly assigned 44 healthy college undergraduates to a positive, negative, or neutral affect condition in which they simultaneously viewed images and listened to music that previous studies had shown to induce specific moods. Results indicated that mood induction was successful, and the positive affect group showed a clearly different pattern of IGT performance compared to the other two groups, in that they showed a rapidly established and stable bias favoring the positive expected value (EV) card decks. The negative affect group showed significantly lower bias towards the positive EV decks, although this group was not different from the neutral affect group. Bayesian analyses confirmed these findings. While consistent with SMH, these current findings may be best understood in support of a more general effect of normal mood on cognition as outlined in the broaden-and-build theory of positive emotions.

Hemodynamic correlates of cognition in human infants.

Over the past 20 years, the field of cognitive neuroscience has relied heavily on hemodynamic measures of blood oxygenation in local regions of the brain to make inferences about underlying cognitive processes. These same functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) techniques have recently been adapted for use with human infants. We review the advantages and disadvantages of these two neuroimaging methods for studies of infant cognition, with a particular emphasis on their technical limitations and the linking hypotheses that are used to draw conclusions from correlational data. In addition to summarizing key findings in several domains of infant cognition, we highlight the prospects of improving the quality of fNIRS data from infants to address in a more sophisticated way how cognitive development is mediated by changes in underlying neural mechanisms.

Prosody guides the rapid mapping of auditory word forms onto visual objects in 6-mo-old infants.

Human infants are predisposed to rapidly acquire their native language. The nature of these predispositions is poorly understood, but is crucial to our understanding of how infants unpack their speech input to recover the fundamental word-like units, assign them referential roles, and acquire the rules that govern their organization. Previous researchers have demonstrated the role of general distributional computations in prelinguistic infants' parsing of continuous speech. We extend these findings to more naturalistic conditions, and find that 6-mo-old infants can simultaneously segment a nonce auditory word form from prosodically organized continuous speech and associate it to a visual referent. Crucially, however, this mapping occurs only when the word form is aligned with a prosodic phrase boundary. Our findings suggest that infants are predisposed very early in life to hypothesize that words are aligned with prosodic phrase boundaries, thus facilitating the word learning process. Further, and somewhat paradoxically, we observed successful learning in a more complex context than previously studied, suggesting that learning is enhanced when the language input is well matched to the learner's expectations.

SMART-T: a system for novel fully automated anticipatory eye-tracking paradigms.

Anticipatory eye movements (AEMs) are a natural and implicit measure of cognitive processing and have been successfully used to document such important cognitive capacities as learning, categorization, and generalization, especially in infancy (McMurray & Aslin, Infancy, 6, 203-229, 2004). Here, we describe an improved AEM paradigm to automatically assess online learning on a trial-by-trial basis, by analyzing eye gaze data in each intertrial interval of a training phase. Different measures of learning can be evaluated simultaneously. We describe the implementation of a system for designing and running a variety of such AEM paradigms. Additionally, this system is capable of a wider variety of gaze-contingent paradigms, as well as implementations of standard noncontingent paradigms. Our system, Smart-T (System for Monitoring Anticipations in Real Time with the Tobii), is a set of MATLAB scripts with a graphical front end, written using the Psychophysics Toolbox. The system gathers eye gaze data using the commercially available Tobii eye-trackers via a MATLAB module, Talk2Tobii. We report a pilot study showing that Smart-T can detect 6-month-old infants' learning of simple predictive patterns involving the disappearance and reappearance of multimodal stimuli.

Near-infrared spectroscopy: a report from the McDonnell infant methodology consortium.

Near-infrared spectroscopy (NIRS) is a new and increasingly widespread brain imaging technique, particularly suitable for young infants. The laboratories of the McDonnell Consortium have contributed to the technological development and research applications of this technique for nearly a decade. The present paper provides a general introduction to the technique as well as a detailed report of the methodological innovations developed by the Consortium. The basic principles of NIRS and some of the existing developmental studies are reviewed. Issues concerning technological improvements, parameter optimization, possible experimental designs and data analysis techniques are discussed and illustrated by novel empirical data.

The quest for generalizations over consonants: asymmetries between consonants and vowels are not the by-product of acoustic differences.

Consonants and vowels may play different roles during language processing, consonants being preferentially involved in lexical processing, and vowels tending to mark syntactic constituency through prosodic cues. In support of this view, artificial language learning studies have demonstrated that consonants (C) support statistical computations, whereas vowels (V) allow certain structural generalizations. Nevertheless, these asymmetries could be mere by-products of lower level acoustic differences between Cs and Vs, in particular the energy they carry, and thus their relative salience. Here we address this issue and show that vowels remain the preferred targets for generalizations, even when consonants are made highly salient or vowels barely audible. Participants listened to speech streams of nonsense CVCVCV words, in which consonants followed a simple ABA structure. Participants failed to generalize this structure over sonorant consonants (Experiment 1), even when vowel duration was reduced to one third of that of consonants (Experiment 2). When vowels were eliminated from the stream, participants showed only a marginal evidence of generalizations (Experiment 4). In contrast, participants readily generalized the structure over barely audible vowels (Experiment 3). These results show that different roles of consonants and vowels cannot be readily reduced to acoustical and perceptual differences between these phonetic categories.

An interaction between prosody and statistics in the segmentation of fluent speech.

Sensitivity to prosodic cues might be used to constrain lexical search. Indeed, the prosodic organization of speech is such that words are invariably aligned with phrasal prosodic edges, providing a cue to segmentation. In this paper we devise an experimental paradigm that allows us to investigate the interaction between statistical and prosodic cues to extract words from a speech stream. We provide evidence that statistics over the syllables are computed independently of prosody. However, we also show that trisyllabic sequences with high transition probabilities that straddle two prosodic constituents appear not to be recognized. Taken together, our findings suggest that prosody acts as a filter, suppressing possible word-like sequences that span prosodic constituents.

Why is language unique to humans?

Cognitive neuroscience has focused on language acquisition as one of the main domains to test the respective roles of statistical vs. rule-like computation. Recent studies have uncovered that the brain of human neconates displays a typical signature in response to speech sounds even a few hours after birth. This suggests that neuroscience and linguistics converge on the view that, to a large extent, language acquisition arises due to our genetic endowment. Our research has also shown how statistical dependencies and the ability to draw structural generalizations are basic processes that interact intimately. First, we explore how the rhythmic properties of language bias word segmentation. Second, we demonstrate that natural speech categories play specific roles during language acquisition: some categories are optimally suited to compute statistical dependencies while other categories are optimally suited for the extraction of structural generalizations.

Language from a biological perspective.

The faculty of language is unique to the human species. This implies that there are human-specific biological changes that lie at the basis of human language. However, it is not clear what the nature of such changes are, and how they could be shaped by evolution. In this paper, emphasis is laid on describing language in a Chomskyan manner, as a mental object. This serves as a standpoint to speculate about the biological basis of the emergence and evolution of language.