Short-term audio-tactile training affects cortical auditory speech-envelope tracking for incongruent but not congruent stimuli.

Integrating auditory and visual information can improve intelligibility and neural tracking of the speech envelope. Speech-relevant tactile information also improves tracking, yet effects on intelligibility are mixed, possibly due to no regular exposure to speech-relevant tactile information. We used short-term audio-tactile training to advance understanding of audio-tactile integration during speech perception. 64 younger adult participants (aged 18-29) took part over five days, during which electroencephalography was recorded. Participants completed a speech-in-noise task, with audio-tactile and audio-only stimuli. They then received training with either tactile information that was congruent with sentences heard (trained group) or incongruent (pseudo-trained group). After three training sessions, participants completed the speech-in-noise task again. Two weeks later, participants returned for a follow-up. Effect of session (pre- or post-training) on speech intelligibility was significant, with no significant effect of group (trained, or pseudo-trained) or stimulus (audio-only, or audio-tactile). Before training, there was a significant increase in speech-envelope tracking accuracy with audio-tactile stimuli, suggesting enhanced neural representation of audio-tactile stimuli. However, there was no benefit of congruent training to audio-tactile tracking. There was an enhancement of audio-only speech-envelope tracking following incongruent training. This suggests that speech intelligibility and tracking of audio-tactile speech are not enhanced by short-term training. This work challenges prevailing assumptions by demonstrating increased speech-envelope tracking accuracy that was not linked to enhanced speech intelligibility. However, these findings are limited to short-term, bottom-up audio-tactile training. Alternate training approaches and further controls, such as tactile-only sentences or audio-only training groups, should be explored in future research.