Thursday, November 26, 2015

Critical period

This entry might sound a little weird, because it was originally an email that I wrote to Dr. Tran, who asked me to write about what I think about the 'critical period'.  But then I kept writing, and decided that it was long enough for a blog.

There are a few things I can say about it from first-hand experience: stereopsis recovery is difficult as hell for me, as an adult.  I can't say what it's like as a child because I knew nothing about vision therapy as a child.

The 'critical period' is something that's come up quite a lot in DIY Vision Therapy.

The knowledge that brain malleability decreases with age is not new. What seems to be new is the emphasis that brain plasticity is always available, even in old age. That's why Sue Barry's Fixing My Gaze was such a surprising book to so many people: that someone 50 years of age--well beyond the critical period--could use her available plasticity to restore full vision.

It's a good book, and it's great that it inspires hope in many, but I also sort of hoped that perhaps she expressed exactly how difficult stereopsis recovery can be for adults. There's a tendency for scientists to overemphasize their findings. So there's a lot of new literature about neuroplasticity in old age, and as a result there's almost a dismissal of the critical period, which in my estimation is real. I think the book made many adults realize 'hey, I think I have that.' and then they try fixing their vision, and only then do they realize how challenging it is.

I've even had conversations with VTs in my group about this. You could ask them 'Do you notice whether it's easier for children to fix their vision?' The invariable answer is that it's much easier for children to fix their vision. One VT said that they fix their vision without even trying. It just takes very gentle nudging at those early ages. It's sort of like when they used the stars to navigate ships. Any small miscalculation can have giant consequences later on. They might land on an entirely different continent. If some small intervention isn't made when the child is still brand new, then the consequences can be rather giant later. He might have severely downgraded vision for the rest of his life as result.

I dated a woman for a while who had a three year old with strabismus. They were going through their options and she had been thinking about giving him surgery. I advised against it and recommended vision therapy or anything else first. I met the kid and even had him try playing Ring Runner with my DK2 (it's too much for a three year old). Fortunately the doctors gave him extra-strength prescription glasses. When he had them off, he said he could see three of me, and when he put them on, he saw one of me. She said that she never had to tell him to use the glasses. He would always automatically use them.  I suggested that she do some tracking exercises to make sure his eyes diverge and converge correctly. After a few weeks of using these new glasses, she informed me that he was able to pass the Butterfly Test--some test for gauging stereoscopy. So he never even had to do vision therapy. He just got proper early intervention and as a result he's going to be able to completely avoid the problems that so many adults later would have. Lucky kid.

So that's about where I am in regard to the critical period. It's definitely a real thing. Vision therapy is much harder for adults, but it is not impossible. With the right guidance and the right amount of dedication and understanding it can be done.

I've heard James talk a bit about the critical period in a podcast. He said he thinks part of the potential of VR HMDs is that they are able to provide a level of stimulation that's very difficult to match in the real world. So even if you have low plasticity compared to, say, a child, the stimulus-power of the DK2, for instance, can sort of overcome that decreased plasticity and allow for changes anyway.

A possible confounding factor that I sort of doubt anyone really considers is genetic variability between people. There is an incredible amount of genetic diversity between people. There is incredible potential for people to be different from one another. MLB baseball players for instance--are genetic mutants. They, on average, have 20/12 acuity!

Susan Barry is a neuroscientist from Princeton! She has a good brain--a brain that's probably not exclusively good for thinking--but rather, generally good. Good brains are caused by genes because genes create brains. Unfortunately there are many people out there with 9-volt brains. I am positive that her good brain has had some influence on her ability to recover stereopsis as quickly as she did.

That's in a nutshell what I think about the critical period. The critical period is real. Neuroplasticity is real. Vision therapy is difficult for adults almost without exception. If you're an adult and you want to recover full vision, it's going to be a huge pain in the ass, but it can be done. There are all kinds of confounding factors like genetic variability which mean that vision therapy is going produce different results for different people. I am hopeful that VR HMDs and other technologies will help enable us to change our visual systems, perhaps by pegging our old recalcitrant brains with supernormal levels of stimulation to convince them to see things differently.



  1. About the critical period, these two courses:
    1. The Brain and Space
    2. The Bilingual Brain

    Hubel and Wiesel are the scientists who first came up with the concept and whose groundbreaking research led them to a nobel prize.
    We don't learn things the same way as kids or adults, simply because the brain in children hasn't developed its prefrontal cortex part (responsible for consciousness).
    As kids we learn one thing as a "whole", as adults we break it up.
    Each way of learning as some advantages. The way we learn things as adults seems to make us more immune to interferences. That applies pretty much to any skill: music, language, golf.
    Our brain is plastic as long as the hippocampus works so we can form new memories. As research moves on, I'm sure new methods will appear that are more targeted to the way adults learn.

    1. With the way you describe it, it sounds like children chunk larger 'chunks'.

      Adults see the parts of the system, and so their interaction with whole systems seems a bit slower.

      Children interact with whole systems. So they're really really fast, but they can also be very easily tricked because they don't know how the systems work. They don't see the constituent parts.