Ambient noise makes it difficult for even those with good hearing to understand speech. It is even more difficult for hearing impaired people with hearing aids. Your hearing system can only insufficiently filter out the sounds relevant for speech from the background noise. A research team has now developed an unusual solution for this: a small vibration module held between the thumb and forefinger triggers stimuli in the brain that promote language comprehension, as initial tests have shown. This approach could open up new possibilities to improve the speech understanding of the hard of hearing.
Disturbing noises such as loud music, clinking cutlery in the restaurant or the babble of voices make it difficult for even hearing people to follow the conversation. “Language is a highly complex acoustic signal that requires similarly complex hierarchical processing processes to be understood,” explain Pierre Guilleminot from Imperial College London and Tobias Reichenbach from the Friedrich-Alexander University of Erlangen-Nuremberg. “These processes include the division and analysis of individual phonemes, syllables and words in order to decode the semantic content.” It is all the more astonishing that our brain can usually do this even in the presence of strong background noise. However, this no longer works so well for people who are hard of hearing: Especially with hearing aids, they often have great difficulty understanding the person they are talking to in noisy environments.
Vibration impulses in time with the language
In their search for a solution to this problem, Guilleminot and Reichenbach took what appeared to be an unusual approach: They investigated whether vibration pulses could improve speech understanding. The background is the theory that multisensory aspects play a role in many perceptions, including the processing of speech sounds. In the brain, stimuli from different sensory channels can therefore influence each other and thus favor or disturb each other. To check this, the researchers conducted a hearing experiment with vibration support on 19 volunteers. For this purpose, the test persons with normal hearing were played English sentences and words amidst dense background noise via headphones.
At the same time, all test subjects held a small device between the thumb and forefinger of their right hand. This emitted slight vibration stimuli parallel to the speech being heard. The impulses were comparable to the slight vibration that many smartphone displays give off as tactile feedback when touched, for example. The vibration stimuli were adjusted in such a way that they were delivered in time with the speech syllables. In several runs, the researchers varied the delay in the vibration signals and also carried out additional test runs with or without impulses placed at random.
improved language understanding
The tests showed that if the tactile stimuli were given in time with the syllables of speech and without a time delay, they improved the subjects’ speech understanding: “Comprehension of the speech, despite background noise, then improves by 6.3 percent compared to the pseudo-impulses,” reports Guilleminot and Reichenbach. This was also confirmed in brain wave measurements during the experiments: The brain activity in the auditory cortex – recognizable by the wave patterns occurring in time with the syllables – was higher during the vibration tests than in the control experiments, as the team determined. “We have thus shown that tactile pulses, which follow the rhythm of speech syllables, can influence and improve understanding of the speech signal underlaid with background noise,” the researchers write.
According to the scientists, this could open up new possibilities for using multisensory hearing aids to help hearing-impaired people understand speech. However, it still needs to be examined more closely how precisely the vibration signals have to follow the beat of the syllables. Guilleminot and Reichenbach also want to find out whether this tactile stimulus can also unfold its multisensory effect directly on the ear. If that were the case, the vibrators could be integrated directly into the hearing aid.
Source: Pierre Guilleminot (Imperial College London) and Tobias Reichenbach (Friedrich-Alexander-Universität Erlangen-Nürnberg), Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2117000119