Impaired neural encoding of naturalistic audiovisual speech in autism.

Researchers studied how autistic teens and young adults process speech when they can both see and hear someone talking. They found that autistic participants had more difficulty understanding speech and showed different brain activity patterns when watching and listening to someone speak at the same time. However, when only listening (without visual cues), both autistic and non-autistic participants performed similarly. This suggests autistic individuals may have specific challenges combining visual and auditory information during natural conversation.

This study used high-density EEG to examine neural processing of naturalistic audiovisual speech in 23 adolescents/young adults with ASD compared to 19 typically developing controls. Participants completed speech detection tasks under auditory-only, visual-only, and audiovisual conditions with varying background noise levels. Linear encoding models assessed cortical tracking of speech envelope and phonetic features. Results showed that while both groups performed similarly in auditory-only conditions, the ASD group demonstrated significantly reduced behavioral performance and weaker neural tracking of both acoustic and phonetic features during audiovisual speech processing.

This provides the first converging behavioral and neurophysiological evidence of impaired multisensory integration for continuous, natural speech in autism.

Findings suggest interventions should target multisensory integration skills rather than auditory processing alone. May inform development of communication strategies that account for visual processing differences. Results support need for environmental modifications in educational and therapeutic settings to optimize speech comprehension for autistic individuals.

Small sample sizes (23 ASD, 19 controls). Study focused on adolescents and young adults, limiting generalizability across age ranges. Cross-sectional design prevents understanding of developmental trajectories. Abstract does not specify participant characteristics or potential confounding variables.

Visual cues from a speaker's face can significantly improve speech comprehension in noisy environments through multisensory integration (MSI)-the process by which the brain combines auditory and visual inputs. Individuals with Autism Spectrum Disorder (ASD), however, often show atypical MSI, particularly during speech processing, which may contribute to the social communication difficulties central to the diagnosis. Understanding the neural basis of impaired MSI in ASD, especially during naturalistic speech, is critical for developing targeted interventions. Most neurophysiological studies have relied on simplified speech stimuli (e.g., isolated syllables or words), limiting their ecological validity.

In this study, we used high-density EEG and linear encoding and decoding models to assess the neural processing of continuous audiovisual speech in adolescents and young adults with ASD (N = 23) and age-matched typically developing controls (N = 19). Participants watched and listened to naturalistic speech under auditory-only, visual-only, and audiovisual conditions, with varying levels of background noise, and were tasked with detecting a target word. Linear models were used to quantify cortical tracking of the speech envelope and phonetic features. In the audiovisual condition, the ASD group showed reduced behavioral performance and weaker neural tracking of both acoustic and phonetic features, relative to controls.

In contrast, in the auditory-only condition, increasing background noise reduced behavioral and model performance similarly across groups. These results provide, for the first time, converging behavioral and neurophysiological evidence of impaired multisensory enhancement for continuous, natural speech in ASD. SIGNIFICANCE STATEMENT: In adverse hearing conditions, seeing a speaker's face and their facial movements enhances speech comprehension through a process called multisensory integration, where the brain combines visual and auditory inputs to facilitate perception and communication. However, individuals with Autism Spectrum Disorder (ASD) often struggle with this process, particularly during speech comprehension.

Previous findings using simple, discrete stimuli do not fully explain how the processing of continuous natural multisensory speech is affected in ASD. In our study, we used natural, continuous speech stimuli to compare the neural processing of various speech features in individuals with ASD and typically developing (TD) controls, across auditory and audiovisual conditions with varying levels of background noise. Our findings showed no group differences in the encoding of auditory-alone speech, with both groups similarly affected by increasing levels of noise. However, for audiovisual speech, individuals with ASD displayed reduced neural encoding of both the acoustic envelope and the phonetic features, marking neural processing impairment of continuous audiovisual multisensory speech in autism.