Augmenting Speech Comprehension using Rapid Frequency Tagging

Speech comprehension under adverse listening conditions benefits from visual speech, but whether visual input can be modulated to improve listening remains unclear. Here we used rapid frequency tagging, a non-invasive sensory stimulation technique, in which the visual tag at 55 Hz over the mouth region of a talking face was amplitude-modulated by the envelope of either the task-relevant or task-irrelevant speech stream. When the visual modulation followed the task-relevant speech envelope, comprehension improved relative to task-irrelevant modulation and to an unmodulated tagging control. MEG responses showed enhanced 55 Hz visual tagging, altered 40 Hz auditory tagging and a non-linear 15 Hz intermodulation. Individual comprehension gains were associated with intermodulation responses in left inferior frontal cortex, linking behavioural benefit to audiovisual interaction. These findings show that task-relevant visual stimulation can improve comprehension by strengthening audiovisual interaction, establishing amplitude-modulated frequency tagging as a tool for probing and supporting comprehension in challenging environments.