Newborn infants differently process adult directed and infant directed speech

Processing of visual stimuli following infant directed speech: Attention-guiding effects of unfamiliar speech

This study investigates attention modulation as a function of infant directed (ID) versus adult directed (AD) speech in seven-month-old infants using electroencephalographic measures. In three experiments, infants were presented with either ID speech or AD speech as stimuli, followed by highly variable images of inanimate objects as targets. In Experiment 1 (N = 18), images were preceded by ID or AD speech with semantic content ("Look here"). Contrary to hypothesis, targets preceded by AD speech elicited increased amplitude of the Negative central (Nc) component compared to targets preceded by ID speech, indicating increased attention. Experiment 2 (N = 23) explored whether ID versus AD speech influences attention allocation also without semantic content. The same targets were either preceded by human voice sounds without semantic content ("Uh-Ah") following the prosody of either ID or AD speech register. No differences in attention allocation or object processing were observed. Experiment 3 (N = 18) contrasted ID speech with and without semantic content and found enhanced attention allocation following stimuli without semantic content, but increased object processing following stimuli with semantic content. Overall, the effects observed here are consistent with the idea that less familiar speech stimuli increase attention for subsequent objects. Semantic content of stimuli increased the depth of object processing in 7-month-olds.

Prerequisites of language acquisition in the newborn brain

Learning to decode and produce speech is one of the most demanding tasks faced by infants. Nevertheless, infants typically utter their first words within a year, and phrases soon follow. Here we review cognitive abilities of newborn infants that promote language acquisition, focusing primarily on studies tapping neural activity. The results of these studies indicate that infants possess core adult auditory abilities already at birth, including statistical learning and rule extraction from variable speech input. Thus, the neonatal brain is ready to categorize sounds, detect word boundaries, learn words, and separate speech streams: in short, to acquire language quickly and efficiently from everyday linguistic input.

Dog brains are sensitive to infant- and dog-directed prosody

When addressing preverbal infants and family dogs, people tend to use specific speech styles. While recent studies suggest acoustic parallels between infant- and dog-directed speech, it is unclear whether dogs, like infants, show enhanced neural sensitivity to prosodic aspects of speech directed to them. Using functional magnetic resonance imaging on awake unrestrained dogs we identify two non-primary auditory regions, one that involve the ventralmost part of the left caudal Sylvian gyrus and the temporal pole and the other at the transition of the left caudal and rostral Sylvian gyrus, which respond more to naturalistic dog- and/or infant-directed speech than to adult-directed speech, especially when speak by female speakers. This activity increase is driven by sensitivity to fundamental frequency mean and variance resulting in positive modulatory effects of these acoustic parameters in both aforementioned non-primary auditory regions. These findings show that the dog auditory cortex, similarly to that of human infants, is sensitive to the acoustic properties of speech directed to non-speaking partners. This increased neuronal responsiveness to exaggerated prosody may be one reason why dogs outperform other animals when processing speech.

Reification of infant-directed speech? Exploring assumptions shaping infant-directed speech research

The seemingly ubiquitous tendency of caregivers to speak to infants in special ways has captivated the interest of scholars across diverse disciplines for over a century. As a result, this phenomenon has been characterized in quite different ways. Here, we highlight the shift from early definitions of “baby-talk” which implied that the nature of speech directed towards infants would vary in different sociolinguistic contexts, to later terms such as “motherese” or “infant-directed speech” (IDS) which came to refer to a specific set of features, some of which were argued to represent a universal, optimal and culturally invariant form of speech. These divergent conceptualizations of IDS thus reflect broader disciplinary tensions pertaining to the role allotted to cultural processes in psychological research. We hope to contribute to this literature by pointing to the complexity associated with identifying discrete categories of speech (i.e., baby-talk and motherese/IDS) within a complex multi-dimensional sociolinguistic landscape. We also highlight ways in which a lack of attention to the cultural context of infant-caregiver interactions may have led to biased characterizations of IDS. Furthermore, these biases may implicitly penetrate the nature of empirical work on IDS as well. We end with a series of suggestions for future directions.

Natural Infant-Directed Speech Facilitates Neural Tracking of Prosody

Infants prefer to be addressed with infant-directed speech (IDS). IDS benefits language acquisition through amplified low-frequency amplitude modulations. It has been reported that this amplification increases electrophysiological tracking of IDS compared to adult-directed speech (ADS). It is still unknown which particular frequency band triggers this effect. Here, we compare tracking at the rates of syllables and prosodic stress, which are both critical to word segmentation and recognition. In mother-infant dyads (n=30), mothers described novel objects to their 9-month-olds while infants' EEG was recorded. For IDS, mothers were instructed to speak to their children as they typically do, while for ADS, mothers described the objects as if speaking with an adult. Phonetic analyses confirmed that pitch features were more prototypically infant-directed in the IDS-condition compared to the ADS-condition. Neural tracking of speech was assessed by speech-brain coherence, which measures the synchronization between speech envelope and EEG. Results revealed significant speech-brain coherence at both syllabic and prosodic stress rates, indicating that infants track speech in IDS and ADS at both rates. We found significantly higher speech-brain coherence for IDS compared to ADS in the prosodic stress rate but not the syllabic rate. This indicates that the IDS benefit arises primarily from enhanced prosodic stress. Thus, neural tracking is sensitive to parents' speech adaptations during natural interactions, possibly facilitating higher-level inferential processes such as word segmentation from continuous speech.

Word class and word frequency in the MMN looking glass

The effects of lexical meaning and lexical familiarity on auditory deviance detection were investigated by presenting oddball sequences of words, while participants ignored the stimuli. Stimulus sequences were composed of words that were varied in word class (nouns vs. functions words) and frequency of language use (high vs. low frequency) in a factorial design with the roles of frequently presented stimuli (Standards) and infrequently presented ones (Deviants) were fully crossed. Deviants elicited the Mismatch Negativity component of the event-related brain potential. Modulating effects of lexical meaning were obtained, revealing processing advantages for denotationally meaningful items. However, no effect of word frequency was observed. These results demonstrate that an apparently low-level function, such as auditory deviance detection utilizes information from the mental lexicon even for task-irrelevant stimuli.

Speech Intonation Induces Enhanced Face Perception in Infants

Infants' preference for faces with direct compared to averted eye gaze, and for infant-directed over adult-directed speech, reflects early sensitivity to social communication. Here, we studied whether infant-directed speech (IDS), could affect the processing of a face with direct gaze in 4-month-olds. In a new ERP paradigm, the word 'hello' was uttered either in IDS or adult-direct speech (ADS) followed by an upright or inverted face. We show that the face-specific N290 ERP component was larger when faces were preceded by IDS relative to ADS. Crucially, this effect is specific to upright faces, whereas inverted faces preceded by IDS elicited larger attention-related P1 and Nc. These results suggest that IDS generates communicative expectations in infants. When such expectations are met by a following social stimulus - an upright face - infants are already prepared to process it. When the stimulus is a non-social one -inverted face - IDS merely increases general attention.

Infants' expectations about the recipients of infant-directed and adult-directed speech

Across cultures, adults produce infant-directed speech (IDS) when addressing infants. We explored whether infants expect IDS to be directed at infants and adult-directed speech (ADS) to adults. Infants from Spain and Turkey (12-15 months) watched animated videos with geometric figures, where one adult figure talked to an infant or another adult figure, while they were gazing at each other (Experiments 1 and 2). In some events, the adult figure addressed the infant figure with IDS, or the other adult figure with ADS (congruent); and in others, the same adult figure addressed the other adult figure with IDS or the infant figure with ADS (incongruent). Both groups of infants showed greater looking at incongruent than congruent events. This preference disappeared when the two figures gazed away from each other (Experiment 3). Thus, by 12 months of age, infants have nuanced expectations that different speech registers such as IDS and ADS are appropriate for addressing different recipients in third-party communicative contexts.