Natures wonders: how vision works (Introduction)

by David Turell @, Thursday, March 28, 2019, 13:44 (327 days ago) @ David Turell
edited by David Turell, Thursday, March 28, 2019, 14:12

The type of vision we have evolved long before we appeared on the scene:

"We see things because objects reflect light that is projected onto our retina, and once our photoreceptors register the light, they send a neural signal down the optic nerve. As we have learned earlier on, perception does not take place in the eyes, and lots of complex neural computations are required before we can experience the world. Neural signals are initiated in the retina and then pass via different neural centers to the visual cortex and higher cortical areas, which eventually build a mental representation of the outside world. Neural processing is not instantaneous because neural signals are passed along neurons at a finite speed. It takes about a tenth of a second for the light registered by the retina to become a visual perception in the brain. This means that our perception lags about a tenth of a second behind what is happening in the world. I will give you a few moments for this thought to settle, and just in case you are still struggling to come to terms with it, let me help you with an analogy: During a thunderstorm, vast amounts of electrical energy are discharged, which results in a flash and a loud bang. As you watch the storm from a distance, you see the lighting before you hear the thunder. This is, of course, because sound travels much slower than light, and so we hear the thunder several seconds after the electrical discharge has occurred. It is the same for perception. The neural delay means that we perceive things at least a tenth of a second after they have occurred.

"You might think that a tenth-of-a-second delay makes very little difference to your morning commute, but believe me, this is a substantial delay. Let me put it in context: if you are walking at a modest speed of about one meter per second, a tenth-of-a-second delay will result in you perceiving the world as lagging 10 centimeters behind you. This is quite hard to believe because you simply do not experience the world as lagging, and such a perceptual error should certainly result in many early-morning collisions. Likewise, this perceptual delay should make it impossible for you to catch a ball, especially because this perceptual delay does not account for the substantially longer amount of time your brain requires to plan and initiate a motor response capable of catching the ball.

"It is only once you start thinking about some of the huge day-to-day challenges our visual system constantly faces that the true wonders of the brain start to emerge. Our brain uses a really clever and almost science-fictional trick that prevents us from living in the past: we look into the future. Our visual system is continuously predicting the future, and the world that you are now perceiving is the world that your visual system has predicted to be the present in the past. This idea takes a bit of time to get used to, and the first time I heard it, I thought it must be crazy. However, unless we predict the future, we will always experience the past."

Comment: And this amazing system that helps us perceive the world could not have arisen by chance. It also shows why Libet's brain delay studies do not apply.

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