gms | German Medical Science

Selective attention enables individuals to prioritize relevant auditory information while suppressing competing distractions, facilitating tasks like understanding a single speaker in a crowded environment. The neural mechanisms of selective attention to speech have predominantly been studied through low-frequency brain responses in the auditory cortex, linked to the rhythms of phonemes, syllables, and words. However, emerging evidence from EEG studies indicates that selective attention also modulates subcortical neural responses [1], [2], specifically the speech frequency-following response (speech-FFR), which reflects neural encoding of the fundamental frequency of speech and its harmonics. While recent Magnetoencephalography (MEG) studies have identified cortical contributions to the speech-FFR [3], [4], [5], it remains unclear whether these cortical contributions are similarly influenced by selective attention.

In this study, we utilized MEG and subsequent source reconstruction to investigate how selective attention modulates cortical contributions to the speech-FFR. MEG data were recorded from 22 healthy, normal-hearing participants while they listened to continuous speech stimuli from two competing male speakers over 40 minutes. Participants were instructed to alternate their attention between the two speakers at regular intervals [6]. To analyze the data, we computed neural responses at the fundamental frequency using neural source estimation and source-level temporal response functions (TRFs). We then compared the cortical speech-FFR for each speaker when they were supposed to be attended versus ignored.

Our findings demonstrated a robust effect of selective attention on cortical contributions to the speech-FFR. Neural responses to the fundamental frequency of the target speaker were significantly enhanced compared to the distractor speaker. This attentional modulation was observed consistently across both the group and individual participant levels. Moreover, independent of attentional focus, the speaker with a lower fundamental frequency elicited stronger cortical contributions to the speech-FFR compared to the speaker with a higher fundamental frequency. These results expand upon previous work by showing that selective attention modulates not only subcortical but also cortical components of the speech-FFR, emphasizing the dynamic interplay between attention and the neural encoding of speech. This study provides novel insights into how cortical mechanisms support selective attention in complex auditory environments and has recently been published in the Journal of Neuroscience [6].