Supertouch

The superhero Daredevil had few powers. His fighting abilities and roof-running were the result of Matt Murdock’s athleticism and a technological ingenuity (DD’s self-made billy club). His true superpowers were his hyper-keen senses (click to enlarge):

The irony, of course, was that the bad guys never knew they were getting taken down by a blind man.

Daredevil’s story follows the belief that if you lose one sense, the others become more sensitive to compensate. This belief is old and common, and in a way, shows that we must have had some inkling about brain plasticity much more than 20 years ago.

If this is so, how does that compensation happen? Is it just a case that those brain centers used for vision automatically repurpose themselves for other sensory modes? Or could it be something more mundane? Blind people are better at some sensory tasks because they practice, practice, practice.

To test this, Wong and colleagues examined the ability of three groups of individuals to detect changes by touch: sighted people, people who were blind, and people who were blind and read Braille.

Of course, this is a simplification, because the blind participants were a very mixed group. Some had been blind since birth, while others had been born with normal vision. Not everyone was equally proficient with Braille.

The test they used was to determine the position of a slotted rod (right). All three groups performed this touch test using their fingertips, and with their lips. (I’m assuming that’s what’s shown in the lower right... though I have never personally seen lips quite that shape.) Using the lips provided a way to test if any differences in touch sensitivity of the Braille readers were due to an increase in touch sensitivity across the board, or if any improvements were found only in the fingertips.

The myth of blind people having sharper senses? Plausible.

There is not an overall enhancement of touch across the board. Blind people did better on the touch task for the fingers, but not with the lips. Further, the more proficient the blind person was with Braille, the better they performed on the task. The results pointed to practice being an important factor – maybe the most important factor – in this increased sensitivity.

Because this paper is in The Journal of Neuroscience, you might expect it to present some data on how the brains of these groups differ. I expected to see some fMRI scans or something similar. To my surprise, there are no brains or neurons or spikes in the methods or results of this paper. It’s straight psychophysics. Next paper, maybe?

This paper is good news for everyone who wants to be a hero. It says that you don’t need to lose your sight to an accidental mysterious toxic waste spill to improve all your other senses. You need dedicated practice. And that’s something that anyone can do.

Reference

Wong M, Gnanakumaran V, Goldreich D. 2011. Tactile spatial acuity enhancement in blindness: evidence for experience-dependent mechanisms. The Journal of Neuroscience 31(19): 7028-7037. DOI: 10.1523/​JNEUROSCI.6461-10.2011