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When I look outside the window while travelling by a car, why do closer things seem to be moving faster and appear unclear but the farther ones seem to be moving slower and appear clear?

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  • $\begingroup$ @BagiM no answers in the comments please $\endgroup$ – AliceD Mar 20 '19 at 9:17
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    $\begingroup$ @AliceD Sorry i thaught the question is going to be moved/deleted since it is not biology so i just left a comment. I can repost the comment as an answer. $\endgroup$ – BagiM Mar 20 '19 at 9:35
  • $\begingroup$ @BagiM: the 2nd half of the question/answer clearly involves some biology. $\endgroup$ – Fizz Mar 20 '19 at 9:40
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    $\begingroup$ @BagiM this is all about perception. Ontopic as can be. Only problemis that OP hasn't gone through any prior effrt, so that would, for me, be a valid reason to put it on hold. $\endgroup$ – AliceD Mar 20 '19 at 9:47
  • $\begingroup$ @Fizz you are probably right. I didn't think of it that way since the same effect of motion blurr would happen for a camera and I thaught of it in terms of physics. But now I see you are right. $\endgroup$ – BagiM Mar 20 '19 at 9:53
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Why do closer things seem to be moving faster?

This is due to parallax. A very simple phenomenon exhaustively explained on wikipedia.

Why do faster moving things appear unclear?

This is primarily due to retinal persistence also well detailed on wikipedia.

It takes time for the retina to detect a change in light at a given position on the retina. Things that move quickly across your visual field (i.e. retina), or that reflect very low amounts of light tend to blur or simply be invisible. Car headlights moving close to you will blur because it takes time for photoreceptors to 'switch off' and the headlights would appear as a streak or trail of light for you. And similarly, if a car were to move at an incredibly large speed, the car wouldn't reflect enough light to trigger a response in the retina, so it would be unseen by you. Remember that what matters here is how much range of your visual field an object crosses, not the speed of the object itself. For example, a fast car in the distance does not blur since it's crossing a tiny fraction of your visual field, but a slow car right in front of your nose will be crossing your entire visual space very quickly.

These are properties of the retina. It is also possible the encoding of visual information in the brain also plays a role in how your perceive something. However, the illusion you describe is entirely explained by these retinal phenomena due to sensory neuron biology.

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    $\begingroup$ It also works the other way around. Flying in a passenger jet at 30K ft seems excruciatingly slow, even though you're moving at ~600 kts, while a single-engine plane doing ~100 kts at treetop level seems quite fast :-) $\endgroup$ – jamesqf Mar 20 '19 at 17:19
  • $\begingroup$ This is not entirely correct. Because of motion parallax an object twice as close moves twice as fast on your retina, correct. But retinal information are next to useless. The whole point of your visual system is to infer what exists in the real world by interpreting retinal inputs. If your visual system was perfect, you would in fact compensate for distance and perceive the 2 objects move at the same speed. What this illusion demonstrates is that vision is not perfect and fails to perfectly take the distance of the objects into account. $\endgroup$ – user37022 Mar 22 '19 at 20:08
  • $\begingroup$ Take this demonstration: put your right thumb at arm-length, and your left thumb and half arm-length. They look the same size right? On your retina your left thumb is in fact half the size of your right thumb. This is not useful information for interacting with the world. What you want to know is the real size of the object. Your visual system compensates for distance and makes you perceive your 2 thumbs at roughly the same size. Speed works the same way. $\endgroup$ – user37022 Mar 22 '19 at 20:12

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