[MUSIC] So hopefully, you appreciate from the last module that, that perceiving the incoming optical information is not, particularly straight forward, or easy and in fact, we have to learn how to see. In others, we have to learn how to perceive, how to interpret all this optical information, and figure out what it represents. And to, to, to convey to you how this works, I'm going to tell you the story of somebody named Mike May and this is the story that's told in a book called Crashing Through by Robert Kurson. And this, the story is that at the age of three and a few months, Mike May was blinded by a chemical accident, so that his corneas were completely scarred over. He then grew up as a blind person and he was, you know, he, he, he is but in that period of his life, he was spectacularly, unafraid. He skied, okay? He was a blind skier. So he, Mike May was unafraid and, and really lead a spectacularly, rich life as a blind person. And in his 30s he became aware that he could actually have corneal transplants. That had the possibility of restoring his vision. And he thought long, and hard about the about whether he wanted to do this and he decided in the end to do it. And luckily, the transplants work. They don't always, but in this case, they worked, and they worked spectacularly, well. So, he, he goes home with completely perfect vision. In other words, getting light from the outside through the cornea, and lens and, and, and into the retina, there are no refractive errors, everything's perfect. So, what, now what does he perceive? And the answer is, that he's able to to see movements. So he goes home, and that day, his, his child kicks a ball, and he goes and he catches it. He can see colors. He can, he recognizes the colors from, the colors that he learned before his accident at three. What he can't see, and what he never can learn is how to recognize faces, how to rec, how to he has very low acuity. One of the stories is that he's walking along the sidewalk, and he sees the lines in the sidewalk, and he's also sees the lines that denote a curb. To him those lines are indistinguishable, he doesn't understand, why the lines in the sidewalk have no meaning, and a line at a curb has a meaning that he has to step down. He can't detect that kind of, of fine difference between very similar appearing objects. He, he can read, but the letters have to be very large in order for him to do so. So, in other words, he has very poor acuity, even though, there's absolutely nothing wrong with his eye, his eyeball. There's nothing wrong in the length or the cornea. He has no refractive error, yet, he can not make sense of this high acuity information. Why? Because he didn't learn it at the right time. And when do you have to learn it? You have to learn it early during a, what's called a sensitive period. And one way to think about a sensitive period is, it's a, it also often called a critical period. But it's a, it's a period, when learning happens very easily and automatically. You don't have to think about it. The baby's not intentionally, learning how to see. A baby's not intentionally, learning a language. But a baby does learn how to see, does learn how to feel, does learn how to interpret language, and to produce language. All these things happen automatically, they happen relatively easily during that sensitive period. So, during that sensitive period, we have to learn how to see. Now, what happens if during that early. Those early years, we, we can't see. So what might be a problem? Well, for instance, might have congenital cataracts. In the Unites States, congenital cataracts are, are removed at birth. But in some parts of the world that is not the case. And what will happen in, in those cases is that the baby will grow up, and let's say they remove the cataracts, and give the person, give the person perfect vision, no refractive errors at age 20, too late. The person cannot make sense of what they're seeing. Another example of this is for Albinos. People with albinism they, there's, there's not, there's too much light bouncing around inside that inside their essentially, white camera. And so there's no high acuity training, and so there's no high acuity vision. So this is, it's really important to learn how to see during a critical period, and to do everything that is going to allow a person to develop normal vision as, an adult. Okay, so, I hope you've enjoyed our trip through vision. We spent a long time out in the eyeball, but in the end, it takes the cerebral cortex, it takes neocortex, to understand all that processing that happened out in the retina, and, and what it means what it means in our lives? In the next meet unit, we're going to turn to hearing. [MUSIC]
