Infants' preference for native audiovisual speech dissociated from congruency preference

Infant selective attention to native and non-native audiovisual speech

The current study utilized eye-tracking to investigate the effects of intersensory redundancy and language on infant visual attention and detection of a change in prosody in audiovisual speech. Twelve-month-old monolingual English-learning infants viewed either synchronous (redundant) or asynchronous (non-redundant) presentations of a woman speaking in native or non-native speech. Halfway through each trial, the speaker changed prosody from infant-directed speech (IDS) to adult-directed speech (ADS) or vice versa. Infants focused more on the mouth of the speaker on IDS trials compared to ADS trials regardless of language or intersensory redundancy. Additionally, infants demonstrated greater detection of prosody changes from IDS speech to ADS speech in native speech. Planned comparisons indicated that infants detected prosody changes across a broader range of conditions during redundant stimulus presentations. These findings shed light on the influence of language and prosody on infant attention and highlight the complexity of audiovisual speech processing in infancy.

A Bayesian meta-analysis of infants' ability to perceive audio-visual congruence for speech

This paper quantifies the extent to which infants can perceive audio-visual congruence for speech information and assesses whether this ability changes with native language exposure over time. A hierarchical Bayesian robust regression model of 92 separate effect sizes extracted from 24 studies indicates a moderate effect size in a positive direction (0.35, CI [0.21: 0.50]). This result suggests that infants possess a robust ability to detect audio-visual congruence for speech. Moderator analyses, moreover, suggest that infants' audio-visual matching ability for speech emerges at an early point in the process of language acquisition and remains stable for both native and non-native speech throughout early development. A sensitivity analysis of the meta-analytic data, however, indicates that a moderate publication bias for significant results could shift the lower credible interval to include null effects. Based on these findings, we outline recommendations for new lines of enquiry and suggest ways to improve the replicability of results in future investigations.

Perception of audiovisual infant directed speech

Infant perception often deals with audiovisual speech input and a first step in processing this input is to perceive both visual and auditory information. The speech directed to infants has special characteristics and may enhance visual aspects of speech. The current study was designed to explore the impact of visual enhancement in infant-directed speech (IDS) on audiovisual mismatch detection in a naturalistic setting. Twenty infants participated in an experiment with a visual fixation task conducted in participants' homes. Stimuli consisted of IDS and adult-directed speech (ADS) syllables with a plosive and the vowel /a:/, /i:/ or /u:/. These were either audiovisually congruent or incongruent. Infants looked longer at incongruent than congruent syllables and longer at IDS than ADS syllables, indicating that IDS and incongruent stimuli contain cues that can make audiovisual perception challenging and thereby attract infants' gaze.

Finding phrases: On the role of co-verbal facial information in learning word order in infancy

The input contains perceptually available cues, which might allow young infants to discover abstract properties of the target language. Thus, word frequency and prosodic prominence correlate systematically with basic word order in natural languages. Prelexical infants are sensitive to these frequency-based and prosodic cues, and use them to parse new input into phrases that follow the order characteristic of their native languages. Importantly, young infants readily integrate auditory and visual facial information while processing language. Here, we ask whether co-verbal visual information provided by talking faces also helps prelexical infants learn the word order of their native language in addition to word frequency and prosodic prominence. We created two structurally ambiguous artificial languages containing head nods produced by an animated avatar, aligned or misaligned with the frequency-based and prosodic information. During 4 minutes, two groups of 4- and 8-month-old infants were familiarized with the artificial language containing aligned auditory and visual cues, while two further groups were exposed to the misaligned language. Using a modified Headturn Preference Procedure, we tested infants’ preference for test items exhibiting the word order of the native language, French, vs. the opposite word order. At 4 months, infants had no preference, suggesting that 4-month-olds were not able to integrate the three available cues, or had not yet built a representation of word order. By contrast, 8-month-olds showed no preference when auditory and visual cues were aligned and a preference for the native word order when visual cues were misaligned. These results imply that infants at this age start to integrate the co-verbal visual and auditory cues.

Audiovisual speech perception and language acquisition in preterm infants: A longitudinal study

BACKGROUND

Preterm infants have a higher risk of language delay throughout childhood. The ability to integrate audiovisual speech information is associated with language acquisition in term infants; however, the relation is still unclear in preterm infant.

AIM AND METHODS

This study longitudinally investigated visual preference for audiovisual congruent and incongruent speech during a preferential looking task using eye-tracking in preterm and term infants at 6, 12, and 18 months of corrected age. The infants' receptive and expressive vocabulary at 12 and 18 months were obtained by parent report, using the Japanese MacArthur Communicative Development Inventory.

RESULTS

We found that preterm infants did not clearly show visual preference for the congruent audiovisual display at any age, whereas term infants looked at the congruent audiovisual display longer than the incongruent audiovisual display at 6 and 18 months. Preterm infants' receptive and expressive vocabulary scores were lower than those of term infants at 12 and 18 months. Furthermore, the proportion of looking time toward the congruent audiovisual display at 6 months was positively correlated with receptive vocabulary scores at 12 and 18 months for both groups.

CONCLUSIONS

These findings suggest that better audiovisual speech perception abilities are one factor that results in better language acquisition in preterm as well as term infants. Early identification of behaviors associated with later language in preterm infants may contribute to planning intervention for developmental problems.

Modality-independent recruitment of inferior frontal cortex during speech processing in human infants

Despite increasing interest in the development of audiovisual speech perception in infancy, the underlying mechanisms and neural processes are still only poorly understood. In addition to regions in temporal cortex associated with speech processing and multimodal integration, such as superior temporal sulcus, left inferior frontal cortex (IFC) has been suggested to be critically involved in mapping information from different modalities during speech perception. To further illuminate the role of IFC during infant language learning and speech perception, the current study examined the processing of auditory, visual and audiovisual speech in 6-month-old infants using functional near-infrared spectroscopy (fNIRS). Our results revealed that infants recruit speech-sensitive regions in frontal cortex including IFC regardless of whether they processed unimodal or multimodal speech. We argue that IFC may play an important role in associating multimodal speech information during the early steps of language learning.

Sources of Confusion in Infant Audiovisual Speech Perception Research

Speech is a multimodal stimulus, with information provided in both the auditory and visual modalities. The resulting audiovisual signal provides relatively stable, tightly correlated cues that support speech perception and processing in a range of contexts. Despite the clear relationship between spoken language and the moving mouth that produces it, there remains considerable disagreement over how sensitive early language learners-infants-are to whether and how sight and sound co-occur. Here we examine sources of this disagreement, with a focus on how comparisons of data obtained using different paradigms and different stimuli may serve to exacerbate misunderstanding.