We live in a very visual age. Image, how we look and dress, and how people perceive us has always been very important and for some today it has even become an overwhelming obsession. Even our language highlights this apparent emphasis on our visual capacities with commonly used expressions such as ‘seeing is believing’, and ‘beauty is in the eye of the beholder’. But are seeing and hearing separate and mutually exclusive functions in the brain?
The latest research is forcing us to take a fresh look at the complex interplay of vision and hearing. It forces us to ask which is more important (from the brain’s perspective), the ability to see or to hear? But more importantly trending research into brain plasticity and the way the brain tries to compensate when brain injuries occur opens up some exciting new avenues of research for dealing with hearing loss.
I hear where you’re coming from
Research into those parts of the brain involved in visual processing has disclosed some remarkable discoveries about the role hearing plays in processing what we see. The research undertaken at the Institute of Neuroscience and Psychology at the University of Glasgow has clearly demonstrated that the visual cortex uses sounds to help predict and create images.
MRI scans demonstrated obvious brain activity in the visual cortex while blindfolded volunteers listened to specific sounds such as birdsong or traffic noise. The brain was clearly forming images from sound input alone.
Why would the brain use sound to see?
The obvious advantage is that being able to form images in the mind before they are actually ‘seen’ would be very helpful for survival. These images help the brain process the visual information much faster enabling us to anticipate potentially dangerous events.
Our hunter/gatherer ancestors hearing a lion roar in the forest could process that information much faster when the sound is associated with an image of the dangerous carnivore. This visual anticipation enabled humans to react before the actual image was seen. On the other hand the sound of calm birdsong would provide an assurance of relative safety allowing the hunter/gatherer to quickly refocus energy on tracking or seeking out important plants.
This might seem very obvious but this type of brain interconnectedness had previously only been observed in monkeys. Seeing such obvious connections in human subjects helps increase our understanding of the role the brain plays in coping with hearing loss.
Are hearing and vision mutually exclusive?
On the other hand we have all seen people who are so involved in some visual task such as texting that they appear to be temporarily deaf to even the most alarming sounds. A University College London (UCL) study measured significant reduction in the ability of the study subjects to hear normal sounds when engaged in challenging visual tasks.
When this inattention deafness occurs it is not simply that the person is ignoring the audio clues. Brain scans take from the volunteers during the study clearly indicated that the brain was switching its focus at a very early stage of the hearing process. In other words the volunteers were literally deaf to the sounds and were not hearing them at all.
This apparent contradiction in the brain’s ability to process sound and vision at the same time suggests that the brain is trying to allocate its limited processing capabilities by prioritizing the inputs. This brings us back to our earlier question: how does the brain decide which is more important, seeing or hearing?
What does that mean for hearing loss?
The brain’s ability to compensate for injuries or transfer function to other parts of the brain has been observed for a long time. There is a large body of research into phantom pain in the case of amputees and more recently similar effects have been noted in the case of tinnitus sufferers.
The concept of brain plasticity and the brain’s ability to adapt and transfer function to other parts of the brain offers some exciting avenues of research into how the brain responds to hearing loss.
It is early days yet and there still many unanswered questions but this kind of research is helping us to gain a clearer picture of the role the brain plays in hearing and promises some real progress towards a solution for hearing loss. Join the https://www.houseofhearing.ca/ blog as we explore these issues further.