Neuropsychology

The blind see sounds

At rush hour, crossing the street in downtown Montreal is no mean feat. You seem to need more than two eyes to see the cars, bicycles, and pedestrians coming at the same time. If it’s that hard for those who see well, how do the blind manage? The answer is both simple and surprising.

According to the latest neuroscience research, the brain adapts to its environment. So, in blind people, the occipital region, generally associated with sight, is converted to hearing. In other words, the blind may hear what others see.

For more than five years, researchers at the Centre for Neuropsychology and Cognition Research (CERNEC) in the Psychology Department have been uncovering the amazing hearing capacity of blind people. As early as 1998, doctoral student Nadia Lessard demonstrated that some congenitally blind people found it easier to localize sounds in space.

“Nadia arranged 16 loudspeakers in an echo-free room,” explains Frédéric Gougoux, a doctoral candidate who is now continuing Ms. Lessard’s work for his thesis. “Sighted and blind subjects, whose heads were immobilized, had to point a finger at the place where sounds produced by each individual loudspeaker were coming from. At the start, the sighted and blind subjects showed similar results. But things got complicated when the subjects were asked to plug one ear. Whereas half the blind subjects always managed to point to the precise locations where the sounds were coming from, the sighted subjects were not able to do so, at all.”

A few years later, a second student, Charles Leclerc, repeated the experiment, with one small difference: he placed electrodes on the subjects’ scalps. Recordings of the brain’s electric activity demonstrated that the region situated at the back became exceptionally active when the blind subjects localized sounds.

Now, another student, Frédéric Gougoux decided to push these findings a little further. Using positron emission tomography, better known as a PET-Scan, he tried to see exactly what was happening in the blind subjects’ brains when they localized sounds. Franco Lepore, a professor in the Psychology Department and Director of CERNEC, and Robert Zatorre, a professor in the Neurology Institute at McGill University, agreed to direct his work. Maryse Lassonde, a professor in the Psychology Department, also agreed to collaborate.

To begin with, Mr. Gougoux tried to recruit the subjects who had already participated in the experiments performed by Nadia Lessard and Charles Leclerc. This was not possible in some cases. But with help from the Nazareth and Louis Braille Institute, the Montreal Association for the Blind and the Metropolitan Montreal Blindness and Amblyopia Association, the student put together his own cohort. All the unsighted subjects selected were either blind at birth or had lost their sight at a young age, before puberty.