Research on crossmodal brain plasticity has not only found that the brain compensates for sensory impairments. For example, so that people who are born blind process auditory information in both the auditory and the visual areas – not just the auditory like the fully sighted. (See our blog for the scientific approach.) It has also shown that the brain adapts to artificial input restoring the impaired senses and computer algorithms translating information from one sense to another. However, while people automatically recognise information processed through their natural crossmodal correspondences (see our blog for the crossmodal correspondences between the senses), they have to learn to learn to interpret the sensations from both brain implants for hearing and sensory substitution devices from vision to hearing (see our blog for A Feel for Art.)
I have invited Carina Sabourin, Yaser Merrikhi, and Stephen G. Lomber, Cerebral Systems Laboratory, McGill University to write this blog post about crossmodal brain plasticity and empowering of sensory abilities. Carina Sabourin, Yaser Merrikhi, and Stephen G. Lomber investigate cortical plasticity in the auditory and visual cortices following hearing loss and the initiation of hearing with cochlear prosthetics. And, recently, in a comprehensive review study, they addressed the question “Do the blind hear better?”.
The idea that blind people can compensate for their lack of vision with enhanced hearing or other abilities, has been around for millennia. Many of the most acclaimed artists from the 8th century BC Greek poet, Homer, to the great jazz musician, Stevie Wonder, lost their vision. Recently, researchers have investigated these anecdotes and confirmed that there is now over-whelming evidence the blind have specific super hearing abilities compared to the sighted1. More excitingly, the brains of blind individuals recruit neural areas that typically handle vision to process auditory information along with hearing brain areas. The ability of typically visual areas to adapt to auditory input is called crossmodal plasticity. The extra brain power crossmodal plasticity provides gives blind individuals their superhuman hearing abilities.
Crossmodal plasticity can occur for other senses beyond hearing too. Deaf individuals recruit hearing brain areas to improve their vision2. Beyond other senses taking advantage of the freed-up brain power, brain plasticity can help the brain adapt to artificial input from brain implants restoring the lost sense. One example is cochlear implants which bypass the inner ear and directly stimulate the auditory nerve giving people with certain types of hearing loss access to sounds. Crossmodal plasticity is thought to help visual and hearing brain areas work together to better process speech. The more teamwork between visual and hearing brain areas, the better cochlear implant users can understand speech3. Similarly, researchers and engineers developing tools for blind people can leverage brain plasticity as well as the specific super hearing abilities of the blind.
One such attempt is sensory substitution devices (SSD) which translate information from one sensory modality into another. Audio-to-visual SSDs convert visual scenes captured by a camera into soundscapes. These devices exploit the improved pitch discrimination4-5 and sound localization abilities6-8 of blind people to convey information about visual environments as the frequency and movement of sounds. SSDs can even use the available brain space in the visual cortex. The part of the visual cortex that recognizes human bodies and tracks their movement was recruited to localize body movement conveyed by an SSD9. The visual reading brain area was even activated by SSDs to enable blind individuals to read with sounds10. Even years after getting their vision back, the visual cortex of individuals who sight was restored through gene therapy was still helping hearing brain areas process sounds11. Some concern exists that crossmodal plasticity may hinder sight restoration from visual brain implants. However, brain plasticity may help the visual and hearing brain areas work together to improve vision outcomes for visual brain implant users, just like it improved the ability of cochlear implant users to understand speech3.
The additional brain power provided by crossmodal plasticity empowers blind individuals with their extraordinary hearing abilities. Researchers and engineers creating tools for the blind can leverage both brain plasticity and their remarkable auditory skills to improve how blind individuals navigate and interact with the world around them.
See our blog for Activities; especially 22-24.
Some suggestions for further listening and watching:
Healing the brain via multisensory technologies and using these to better understand the brain
What Does Blindness or Deafness Tell Us About Brain Development?
What is the function of auditory cortex when it develops in the absence of acoustic input?
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1Sabourin, C. J., Merrikhi, Y., & Lomber, S. G. (2022). Do blind people hear better? Trends in Cognitive Sciences, 26(11), 999-1012. https://doi.org/10.1016/j.tics.2022.08.016
2Bavelier, D., Dye, M. W. G., & Hauser, P. C. (2006). Do deaf individuals see better? Trends in Cognitive Sciences, 10(11), 512-518. https://doi.org/10.1016/j.tics.2006.09.006
3Anderson, C. A., Wiggins, I. M., Kitterick, P. T., & Hartley, D. E. H. (2017). Adaptive benefit of cross-modal plasticity following cochlear implantation in deaf adults. Proceedings of the National Academy of Sciences of the United States of America, 114(38), 10256-10261. https://doi.org/10.1073/pnas.1704785114
4Collignon, O., Dormal, G., Albouy, G., Vandewalle, G., Voss, P., Phillips, C., & Lepore, F. (2013). Impact of blindness onset on the functional organization and the connectivity of the occipital cortex. Brain, 136(9), 2769-2783. https://doi.org/10.1093/brain/awt176
5Rokem, A., & Ahissar, M. (2009). Interactions of cognitive and auditory abilities in congenitally blind individuals. Neuropsychologia, 47(3), 843-848. https://doi.org/10.1016/j.neuropsychologia.2008.12.017
6Chen, Q., Zhang, M., & Zhou, X. (2006). Spatial and nonspatial peripheral auditory processing in congenitally blind people. NeuroReport, 17(13), 1449-1452. https://doi.org/10.1097/01.wnr.0000233103.51149.52
7Lewald, J. (2013). Exceptional ability of blind humans to hear sound motion: Implications for the emergence of auditory space. Neuropsychologia, 51(1), 181-186.
https://doi.org/10.1016/j.neuropsychologia.2012.11.017
8Röder, B., Teder-Salejarvi, W., Sterr, A., Rosler, F., Hillyard, S. A., & Neville, H. J. (1999). Improved auditory spatial tuning in blind humans. Nature, 400(6740), 163-166.
9Striem-Amit, E., & Amedi, A. (2014). Visual Cortex Extrastriate Body-Selective Area Activation in Congenitally Blind People “Seeing” by Using Sounds. Current Biology, 24(6), 687-692. https://doi.org/10.1016/j.cub.2014.02.010
10Striem-Amit, E., Cohen, L., Dehaene, S., & Amedi, A. (2012). Reading with Sounds: Sensory Substitution Selectively Activates the Visual Word Form Area in the Blind. Neuron, 76(3), 640-652. https://doi.org/10.1016/j.neuron.2012.08.026
11Mowad, T. G., Willett, A. E., Mahmoudian, M., Lipin, M., Heinecke, A., Maguire, A. M., Bennett, J., & Ashtari, M. (2020). Compensatory Cross-Modal Plasticity Persists After Sight Restoration. Frontiers in Neuroscience, 14(12 May). https://doi.org/10.3389/fnins.2020.00291
