TORONTO – Ever wondered how we always manage to make our way through various things to reach that jelly at the back of the refrigerator? Well, researchers at The University of Western Ontario have now unlocked the mystery of how our brain allows us to avoid such undesired objects.
Canada Research Chair in Visual Neuroscience Mel Goodale, lead author
“We automatically choose a path for our hand that avoids hitting any obstacles that may be in the way. Every day, we perform hundreds of actions of this sort without giving a moment’s thought as to how we accomplish these deceptively simple tasks,” said Goodale.
For the study, the researchers asked a patient who had become completely blind on his left side following a stroke to the main visual area of the brain to avoid obstacles as he reached out to touch a target in his right – or ‘good’ – visual field.
He could avoid the obstacles as any normal-sighted individual would, but surprisingly, when the experiment was repeated on his blind side, he was still able to avoid them – even though he never reported having seen them.
“The patient’s behaviour shows he is sensitive to the location of obstacles he is completely unaware of,” said Striemer.
“The patient seemed to be as surprised as we were that he could respond to these ‘unseen’ obstacles,” added Goodale.
The findings provide compelling evidence for the idea that obstacle avoidance depends on ancient visual pathways in the brain that appear to bypass the main visual areas that allow us to perceive the world.
Thus, even when the part of the brain that gives us our visual experience is damaged, other parts of the brain still maintain a limited ability to use visual information from the eyes to control skilled movements of the limbs.
Additional experiments have shown that these primitive visual pathways work only in real-time and do not have access to memories, even of the short-term variety.
To explain it, the researchers provided an obstacle in the patient’s blind field but delayed his reach by two seconds, and found that he no longer showed any sensitivity to the object’s location.
The study’s results have important implications for our understanding of what gets lost and what gets spared following damage to the brain’s main visual pathways, and point the way for new approaches to rehabilitation.
The study has been published in the Proceedings of the National Academy of Sciences.