LEUVEN, Belgium — Often, in science, it is something missing that provides a window to insight. Like a brick taken out of a wall, something that is not there can shed the most light on a subject.
In the case of neuroscientists at the Belgian university, Katholieke Universiteit Leuven (KU Leaven), the opportunity to peer through the wall surrounding some of the innermost mysteries of consciousness came from studying subjects who were missing sight itself.
One of the most fundamental processes for navigating the world is categorization. When we see, or otherwise perceive something, we put it in a category such as face, body part, object, or scene. For some time now, scientists have known that part of this ability to sort out the world takes place in the ventral-temporal cortex (VTC) which is associated with the visual brain.
In a new study, KU Leuven researchers have shown that people who have been blind since birth also use this part of the so-called visual brain to perform categorization. This means that sight is not, as some suspected, a prerequisite for the VTC to perform its sorting duties.
“Their visual brain responds in a different way to each category. This means that blind people, too, use this part of the brain to differentiate between categories, even though they’ve never had any visual input,” says study author Hans Op de Beeck in a press release. “And the layout of their map is largely the same as that of sighted people. This means that visual experience is not required to develop category selectivity in the visual brain.”
When the researchers had blind participants listen to sounds associated with faces, such as laughing or kissing, the same parts of their brain showed activity as a sighted person perceiving visual information. The same held true for sounds in other categories, such as hands clapping for body parts, or ocean waves for scenes.
Researchers said these results were especially striking in subjects that were born without eyes, as this meant there was no chance that the subjects brains were influenced by visual input they had as babies.
“Because these subjects are the only participants in our study whom we are certain never had any visual experience, even during a brief period early in life, these results serve as a benchmark for our full pool of blind subjects,” writes Op de Beeck.
Just one part of the puzzle, this research also raises questions about how the auditory information is getting to the visual portion of the blind participants’ brains.
“Another fundamental question regarding categorical representations in VTC concerns the information that is represented,” says Op de Beeck. “What does VTC of the blind person encode when it is presented with auditory stimuli?”
To answer such complex and fundamental questions about the nature of our consciousness and perception of the world, the KU Leuven scientists say one thing is needed: More research!
Their recent findings come alongside other new insights regarding the way blind people navigate and perceive the world, including a study that offers unprecedented details of some blind people’s ability to echolocate using vocal clicks.
The VTC study findings were published recently in The Proceedings of The National Academy of Sciences of The United States of America.