Practice, not loss of sight, improves sense of touch in the blind

New research from McMaster may answer a controversial question: do the blind have a
better sense of touch because the brain compensates for vision loss or because of heavy
reliance on their fingertips?

The study, published in the most recent edition of the Journal of Neuroscience,
suggests daily dependence on touch is the answer.

Twenty-eight profoundly blind participants-with varying degrees of Braille
expertise-and 55 normally sighted adults were tested for touch sensitivity on six fingers
and both sides of the lower lip. Researchers reasoned that, if daily dependence on touch
improves tactile sensitivity, then blind participants would outperform the sighted on all
fingers, and blind Braille readers would show particular sensitivity on their reading
fingers. But if vision loss alone improves tactile sensitivity, then blind participants
would outperform the sighted on all body areas, even those that blind and sighted
people use equally often, such as the lips.

“There have always been these two competing ideas about why blind people have a
better sense of touch,” explains Daniel Goldreich, corresponding author and a professor
in the Department of Psychology, Neuroscience & Behaviour. “We found that
dependence on touch is a driving force here. Proficient Braille readers-those who might
spend hours a day reading with their fingertips-performed remarkably better. But blind
and sighted participants performed equally when the lips were tested for sensitivity.”

Researchers used a specially-designed machine which held the pad of the
participant's fingertip perfectly still for the experiments. While the finger lay over a hole
in the table, the machine pushed rods with textured surfaces through the opening until
they met the fingertip. Researchers asked subjects to identify the patterns by touch. A
similar test was performed on the lower lip.

Not only did blind participants do better than their sighted peers, but Braille
readers, when tested on their reading hands, outperformed nonreaders who were also
blind. For Braille-reading participants, their reading fingers were more sensitive than
their non-reading fingers.

“These results may help us design further experiments to determine how to
improve the sense of touch, which could have applications later in life,” says Mike Wong,
study author and a graduate student in the McMaster Integrative Neuroscience
Discovery & Study program. “Braille is extraordinarily difficult to master, particularly as
an adult. In future we may find new ways to teach Braille to people who have recently
become blind.”

The research was funded by the Natural Sciences and Engineering Research Council
of Canada (NSERC).