The Sight of Touch

There has been some discussion on the Orbit Reader email list about the roll of the visual cortex (the portion of the brain that interprets the signals from your eyes), and one's sense of touch in a person without sight. This is going to be a lengthy passage, but bear with me and I think it will be informative for many of you.

I first learned of the roll that the brain's visual cortex played in the reading of braille through an episode of Scientific American Frontiers, hosted by alan Alda on our local PBS station in November 2000. The entire episode was named "Changing Your Mind." It has several intersting segments about retrainnig or expanding your brain. The first segment, "The Sight Of Touch," focused on how the visual cortex aids in the sense of touch when it is not needed for the interpretation of visual stimuli.

I provide links to an mp3 of that segment, a link to the transcript of the entire episode, and to their web site where you can stream the entire episode if you are interested. But, a personal story first.

I was involved in a study on sleep disorders in the totally blind population at the Oregon Health Science University (OHSU,) in the late 90's and early 2000's. In 2002, OHSU contacted me about another study they were doing and they needed both sighted and blind participants to study if the visual cortex may have a roll in the discrimination of sounds. Their long-term goal was to see if this could help in retraining elderly persons or stroke victims in some way. My sighted wife and I enrolled in the study.

The first part of the study involved sitting at a computer and basically playing a game like the old Simon game. A series of tones would be played at different pitches; certain keys or buttons played each pitch, and your job was to repeat the sequence. The more you got right, the longer the sequence got until you couldn't continue. I apparently did well enough to get into the next part of the study, which was wearing headphones while in an MRI machine and listening to different pairs of sounds and saying if they matched or were different; much like a test you will hear in the segment, The Sight Of Touch.

The first pairs were computer generated tones, some sounded a little like birds, others just random tones; some higher pitched, some lower, etc. Then came the truly challenging pairs. People would read single syllable words like Hog, Dog, and you had to say if it was the same person or a different person. I swear one pair of the voices had to be sisters. They sounded so much alike. I had to really concentrate hard to figure out if they were the same or different.

While I am doing this, my wife is sitting with the technician running the MRI. He is pointing out to her on the screen which part of my brain was lighting up on the MRI. It was the visual cortex. I've been totally blind with no light perception since I was 12. One would think the visual cortex would have simply sat there or some how shrunk. Well, this proved it was quite active.

When I was struggling with the two female voices, the technician pointed to the specific spot in my brain and told my wife, "That is the same part of the brain you would use to distinguish black fabrics."

For those who do not know, if you are comparing black fabrics in a fabric store, or even a clothing store, it is very hard to truly get matching black colors. They have lots of subtle hews in them and the lighting has to be really perfect to get a good match. So, my visual cortex was working overtime to help me distinguish those voices, which is an amazing thing about the brain. It really can completely reallocate its resources.

Below are links to an MP3 file of the almost 12 minute segment of the Scientific American episode called The Sight Of Touch. Then a link to the transcript of the entire episode which runs almost an hour if one is watching/listening to it. Then, a link to stream the entire episode if you want to take the time to watch the whole thing. I think it is worth it.


Scientific American Frontiers Season 11 Episode 1 Changing Your Mind Entire Transcript in a word document

Scientific American Frontiers Season 11 web site

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Last updated September 8, 2021