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

Native speakers of Dutch do not always adhere to prescriptive grammar rules in their daily speech. These grammatical norm violations can elicit emotional reactions in language purists, mostly high-educated people, who claim that for them these constructions are truly ungrammatical. However, linguists generally assume that grammatical norm violations are in fact truly grammatical, especially when they occur frequently in a language. In an fMRI study we investigated the processing of grammatical norm violations in the brains of language purists, and compared them with truly grammatical and truly ungrammatical sentences. Grammatical norm violations were found to be unique in that their processing resembled not only the processing of truly grammatical sentences (in left medial Superior Frontal Gyrus and Angular Gyrus), but also that of truly ungrammatical sentences (in Inferior Frontal Gyrus), despite what theories of grammar would usually lead us to believe

Abstract

In a recent fMRI study we showed that left posterior middle temporal gyrus (LpMTG) subserves the retrieval of a word's lexical-syntactic properties from the mental lexicon (long-term memory), while left posterior inferior frontal gyrus (LpIFG) is involved in unifying (on-line integration of) this information into a sentence structure (Snijders et al., 2009). In addition, the right IFG, right MTG, and the right striatum were involved in the unification process. Here we report results from a psychophysical interactions (PPI) analysis in which we investigated the effective connectivity between LpIFG and LpMTG during unification, and how the right hemisphere areas and the striatum are functionally connected to the unification network. LpIFG and LpMTG both showed enhanced connectivity during the unification process with a region slightly superior to our previously reported LpMTG. Right IFG better predicted right temporal activity when unification processes were more strongly engaged, just as LpIFG better predicted left temporal activity. Furthermore, the striatum showed enhanced coupling to LpIFG and LpMTG during unification. We conclude that bilateral inferior frontal and posterior temporal regions are functionally connected during sentence-level unification. Cortico-subcortical connectivity patterns suggest cooperation between inferior frontal and striatal regions in performing unification operations on lexical-syntactic representations retrieved from LpMTG.