Our remarkable oculomotor system
I wrote in a previous post about being confined to a tiny space as we film Understanding the Brain: The Neurobiology of Everyday Life. Now I am told that my confinement has been imposed upon me because I pace too much. Why would pacing be a problem? Well, it wouldn’t be if I was talking to a live, in-person audience. But a live audience is not exactly a possibility in MOOC-land and pacing is a problem since I am talking to cameras. The problem would be insurmountable if it were not for the skill and attention of dedicated human camera operators.
What do we do that cameras can’t? Well it turns out that we have an oculomotor system that allows us to smoothly and effortlessly track moving objects. We don’t have to think about it and we don’t have to put conscious effort into it. We can follow moving objects in 3 spatial dimensions – horizontal, vertical and depth. A human observer would have no problem maintaining fixation on a person pacing back and forth and to and fro. In contrast, camera lenses, even pricey ones, can’t rival humans in terms of gaze control. No brain, no oculomotor system, no smooth pursuit. Every camera needs a highly skilled operator that manually moves the camera to follow the object (or pacing person) of interest.
Our two camera operators, Ryan and Andy, move the camera to the left and right as I move within my green tape-delimited area. How do they maintain the correct depth of focus? I am sure that most of you have experience with point-and-shoot cameras which automatically focus images. Autofocus places the central portion of an image into focus. Alternatively, camera operators can manually adjust the depth of focus. Autofocus and manual focus each have their downsides: if the center of the image is not the area of interest, autofocus is going to blur the object of interest and manual focus takes time. Camera operators use tricks such as using a small aperture to increase the range of focal depth [we accomplish the same objective by constricting our pupil when we gaze at near objects]. And then, of course, camera operators restrict the movements of those that they are filming….
So how different is the function of our oculomotor system from the operation of a camera by a skilled human? The big difference is that we effortlessly follow objects of interest in all dimensions. Camera operators achieve the same end only with concentration, skill and experience. The temporal lag between movement and focus is far greater in the case of a camera than it is for us. As we track objects moving across our visual field, there is virtually no lag: our extraocular muscles are lightning-fast. There is an accommodation lag, meaning a time delay before our lens shape is changed by parasympathetically controlled smooth muscles. But this accommodation lag is far shorter than the time needed for a human to adjust a camera’s depth of focus. All of this makes me deeply appreciate the marvelous oculomotor system that we all receive for free in our mammalian brains.
In one respect we are very similar to a camera. We adjust the depth of focus for the foveal or central image just as autofocus does. We cannot, for example, adjust our depth of focus for an object in the periphery of our visual field.
While I like to pace, I am happy to have my pacing constrained since it means that I can spread the word about the brain to thousands of interested people. MOOCs are a revolution in learning that we can all believe in!
One final note: filming wrapped up this morning. We are all feeling excited about Understanding the Brain and look forward to our opening day on April 28.