Publications

Abstract

While infants' sensitivity to visual speech cues and the benefit of these cues have been well-established by behavioural studies, there is little evidence on the effect of visual speech cues on infants' neural processing of continuous auditory speech. In this study, we investigated whether visual speech cues, such as the movements of the lips, jaw, and larynx, facilitate infants' neural speech tracking. Ten-month-old Dutch-learning infants watched videos of a speaker reciting passages in infant-directed speech while electroencephalography (EEG) was recorded. In the videos, either the full face of the speaker was displayed or the speaker's mouth and jaw were masked with a block, obstructing the visual speech cues. To assess neural tracking, speech-brain coherence (SBC) was calculated, focusing particularly on the stress and syllabic rates (1–1.75 and 2.5–3.5 Hz respectively in our stimuli). First, overall, SBC was compared to surrogate data, and then, differences in SBC in the two conditions were tested at the frequencies of interest. Our results indicated that infants show significant tracking at both stress and syllabic rates. However, no differences were identified between the two conditions, meaning that infants' neural tracking was not modulated further by the presence of visual speech cues. Furthermore, we demonstrated that infants' neural tracking of low-frequency information is related to their subsequent vocabulary development at 18 months. Overall, this study provides evidence that infants' neural tracking of speech is not necessarily impaired when visual speech cues are not fully visible and that neural tracking may be a potential mechanism in successful language acquisition.

Abstract

The environment in which infants learn language is multimodal and rich with social cues. Yet, the effects of such cues, such as eye contact, on early speech perception have not been closely examined. This study assessed the role of ostensive speech, signalled through the speaker's eye gaze direction, on infants’ word segmentation abilities. A familiarisation-then-test paradigm was used while electroencephalography (EEG) was recorded. Ten-month-old Dutch-learning infants were familiarised with audio-visual stories in which a speaker recited four sentences with one repeated target word. The speaker addressed them either with direct or with averted gaze while speaking. In the test phase following each story, infants heard familiar and novel words presented via audio-only. Infants’ familiarity with the words was assessed using event-related potentials (ERPs). As predicted, infants showed a negative-going ERP familiarity effect to the isolated familiarised words relative to the novel words over the left-frontal region of interest during the test phase. While the word familiarity effect did not differ as a function of the speaker's gaze over the left-frontal region of interest, there was also a (not predicted) positive-going early ERP familiarity effect over right fronto-central and central electrodes in the direct gaze condition only. This study provides electrophysiological evidence that infants can segment words from audio-visual speech, regardless of the ostensiveness of the speaker's communication. However, the speaker's gaze direction seems to influence the processing of familiar words.

Abstract

Communication and integration of information between brain regions plays a key role in healthy brain function. Conversely, disruption in brain communication may lead to cognitive and behavioral problems. Autism is a neurodevelopmental disorder that is characterized by impaired social interactions and aberrant basic information processing. Aberrant brain connectivity patterns have indeed been hypothesized to be a key neural underpinning of autism. In this study, graph analytical tools are used to explore the possible deviant functional brain network organization in autism at a very early stage of brain development. Electroencephalography (EEG) recordings in 12 toddlers with autism (mean age 3.5 years) and 19 control subjects were used to assess interregional functional brain connectivity, with functional brain networks constructed at the level of temporal synchronization between brain regions underlying the EEG electrodes. Children with autism showed a significantly increased normalized path length and reduced normalized clustering, suggesting a reduced global communication capacity already during early brain development. In addition, whole brain connectivity was found to be significantly reduced in these young patients suggesting an overall under-connectivity of functional brain networks in autism. Our findings support the hypothesis of abnormal neural communication in autism, with deviating effects already present at the early stages of brain development

Abstract

Atypical visual perception in people with autism spectrum disorders (ASD) is hypothesized to stem from an imbalance in excitatory and inhibitory processes in the brain. We used neuronal oscillations in the gamma frequency range (30 – 90 Hz), which emerge from a balanced interaction of excitation and inhibition in the brain, to assess contextual modulation processes in early visual perception. Electroencephalography was recorded in 12 high-functioning adults with ASD and 12 age- and IQ-matched control participants. Oscilla- tions in the gamma frequency range were analyzed in response to stimuli consisting of small line-like elements. Orientation-speci fi c contextual modulation was manipulated by parametrically increasing the amount of homogeneously oriented elements in the stimuli. The stimuli elicited a strong steady-state gamma response around the refresh-rate of 60 Hz, which was larger for controls than for participants with ASD. The amount of orientation homogeneity (contextual modulation) in fl uenced the gamma response in control subjects, while for subjects with ASD this was not the case. The atypical steady-state gamma response to contextual modulation in subjects with ASD may capture the link between an imbalance in excitatory and inhibitory neuronal processing and atypical visual processing in ASD