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Infants behave as adults when processing degraded speech, but, is this the case at the brain level?
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Irene Arrieta1, Irene De La Cruz-Pavía, Laurianne Cabrera; 1Integrative Neuroscience and Cognition Center, Université Paris Cité, UFR Biomédicale, 45 rue des Saints Pères, 75006 Paris, France; Basque center on Cognition, Brain and Language, Paseo Mikeletegi 69, 2º 20009 Donostia-San Sebastián, Spain, 2Ramón y Cajal e Ikerbasque Research Fellow, Facultad de Ciencias Sociales y Humanas, Universidad de Deusto, Unibertsitate Etorb., 24, Deusto, 48007 Bilbao, Bizkaia, España, 3ntegrative Neuroscience and Cognition Center, Université de Paris, UFR Biomédicale, 45 rue des Saints Pères, 75006 Paris, France
Background: Language acquisition typically occurs in rich audio-visual, face-to-face interactions, often under suboptimal listening conditions. Yet, much research on early language development has relied on auditory-only paradigms in ideal listening environments. In this study, we investigated how infants process audio-visual speech when intelligibility is reduced. We hypothesised that reduced speech intelligibility would: (1) Increase infants’ attention to the mouth of the speaker; (2) Increase hemodynamic activity in brain areas related to executive functions and processing effort, such as the prefrontal cortex; and (3) Decrease cortical tracking of speech. Method: We tested 47 infants aged 7–9 months, a developmental period characterized by a shift in visual attention from the eyes to the mouth during speech perception. Infants viewed 28 videos of a woman producing continuous infant-directed speech (23–30 s each) with either intact audio or degraded audio (8-band vocoding). During a 12-min session, gaze behaviour and neural activity were recorded simultaneously. Eye tracking was used to assess visual attention to the mouth over the eyes of the speaker, while brain responses were measured using functional near-infrared spectroscopy (fNIRS) to index hemodynamic changes in fronto-temporal regions and electroencephalography (EEG) to quantify neural-speech synchrony using cortical tracking analysis. Results and Discussion: Behavioural results showed that infants significantly increased looking time toward the speaker’s mouth when speech was degraded, suggesting an early compensatory strategy similar to that observed in adults. The fNIRS results showed a decreased brain activity in the left inferior frontal gyrus in the degraded condition, against the second hypothesis that predicted the inverse pattern, due to previous reports of listening effort-related activity in the prefrontal cortex. In addition, brain activity in the frontal cortex is not significantly related to mouth-looking behaviour at the group level. EEG data analysis is still ongoing, with completion planned before the conference and therefore the third hypothesis remains to be statistically tested. This research aimed to establish objective measures of speech intelligibility in young listeners, with potential applications for infants with cochlear implants that receive vocoded speech through their devices.
Topic Areas: Language Development/Acquisition, Multisensory or Sensorimotor Integration