Humans are a vision-centric species, and large parts of our brains are dedicated to processing information we receive through our eyes. But what about the visually impaired who were not able to see since they were born? Dr Łukasz Bola from the JU Institute of Psychology has been researching this subject as part of an international science team. The results of their work have recently been published in Current Biology.
In 2014, a research team at the University of Glasgow have proven that the visual cortex of people with normal eyesight also activates in response to some sounds. The scientists decided to investigate if similar effects can be observed in the case of the congenitally blind. The employed MRI scans to monitor the brain activity of volunteers while they were listening to sounds such as the rustle of a forest, noisy street as well as conversations. As it turned out, even the most basic areas of human visual cortex encode information about sounds.
‘To put it simply, we were able to identify the sounds heard by a person based solely on the activity of their visual cortex. Interestingly enough, despite some differences in being able to correctly identify a sound, the overall result pattern was very similar between the visually impaired and the control group that was previously tested by my colleagues. In both cases, sound were easier to identify based on the activity of the parts of the visual cortex that is normally responsible for processing information about peripheral vision. In turn, the areas the process more central visual stimuli were less helpful’, explained Dr Łukasz Bola, a co-author of the paper published in Current Biology.
To check which sounds are activating the visual cortex, the researchers used algorithms and machine learning. The algorithms were based on partial results, and then tested to see if they were able to correctly determine what kind of sound was processed by the visual cortex. For the most part, the algorithm was able to do that.
‘It seems that the neuroplastic changes in the brain, related to some sort of life experiences, such as the loss of sight, occur only within its general and pre-programmed organisations structure, which cannot be overly modified. Our brains have a great potential for neuroplasticity, but it seems that changes can only happen within strict evolutionary boundaries’, said Dr Łukasz Bola. ‘To some extent, we are facing one of science’s great questions: where exactly lies the line between environmental factors, like culture, and the natural predispositions of our brains. This research project is another step towards finding an answer to that question’, he added.
The researchers still do not know why visual cortex is used to analyse what we hear. One hypothesis is that it may serve to prepare us for what we are about to see, another is that it directs our attention to specific part of our field of vision, particularly the peripheries, where our eyesight is not as sharp as in the centre. In the case of the visually impaired, it is entirely possible that the brain does not perceive their lack of sight, or prevents some of its part from not being used. Research suggests that the mechanism that govern the relationship between visual and auditory cortex are so deeply entrenched in our brains that they are also present in those without the ability to see.
The paper is the result of a research project carried out at the University of Glasgow and the JU Institute of Psychology funded by the National Science Centre. Dr Łukasz Bola, who graduated from and earned his PhD at the Institute, is currently working at Harvard University.