# What's the cause of this visual effect? **URL:** \ **Category:** Factual Questions\ **Created:** [November 14, 2008, 3:53am UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661 "2008-11-14T03:53:41Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [November 14, 2008, 3:53am UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/1 "2008-11-14T03:53:41Z")
And is there a name for it? Imagine that you are riding on a train going, say 30 mph. Another set of tracks runs parallel to the track you are on, a few feet away. Now, if you look straight out of your window, i.e. perpendicular to the other tracks, the railroad ties all blur together, and it is impossible to distinguish individual ties. However, if you look straight ahead (or backwards for that matter), so that your direction of vision approximates the direction of travel, it’s very easy to see each individual tie, and even focus attention on a specific one and monitor (I almost said track) its position relative to the train, until it gets so close that it again becomes a blur. Is this somehow related to the doppler effect (which I really don’t understand) or is it because in the latter case each tie stays in our field of vision for a longer time, giving the brain more opportunity to process the information? Or is it something else? For bonus points, I realized as I was composing this post that I’m not really sure if one train runs on a track, or a pair of tracks. What’s the correct usage? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 14, 2008, 4:01am UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/2 "2008-11-14T04:01:08Z")
Your eyes are tracking individual ties. For ties (or other objects) which are far away from you, your eyes have to move a very small angle to track them, and it’s therefore easy. For nearby objects, though, your eyes have to move a much greater angle, until they can’t keep up any more. ---
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [November 14, 2008, 4:06am UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/3 "2008-11-14T04:06:15Z")
Thanks, **Chronos**. That actually makes sense. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [November 14, 2008, 2:37pm UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/4 "2008-11-14T14:37:37Z")
Is this related at all to the phenomenon where you can see flickering things (old CRT computer monitors/TVs, movies, faulty florescent lights, etc.) better out of the corner of your eye than straight-on? ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [November 14, 2008, 3:39pm UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/5 "2008-11-14T15:39:19Z")
> [@404 Clue Not Found](#): > > Is this related at all to the phenomenon where you can see flickering things (old CRT computer monitors/TVs, movies, faulty florescent lights, etc.) better out of the corner of your eye than straight-on? No, that’s different. The effect \*\*Chronos \*\*describes is due to geometry but what you describe here is due to something else since the object doesn’t move. However, I don’t know what the answer to this one is, unless the persistence of images is shorter in the cells outside the center of your field of view. ---
**Author:** ![RedSwinglineOne](https://avatars.discourse-cdn.com/v4/letter/r/a9adbd/32.png) [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)\ **Post date:** [November 14, 2008, 4:24pm UTC](https://boards.straightdope.com/t/whats-the-cause-of-this-visual-effect/472661/6 "2008-11-14T16:24:41Z")
From Wiki. > [@](#): > > Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Because they are more light-sensitive, rods are responsible for night vision. Named for their cylindrical shape,\*\* rods are concentrated at the outer edges of the retina and are used in peripheral vision\*\*. There are about 120 million rod cells in the human retina. > > A rod cell is sensitive enough to respond to a single photon of light, and is about 100 times more sensitive to a single photon than cones. Because rods require less light to function than cones, they are therefore the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to become activated. Additionally, multiple rod cells converge on a single interneuron, collecting and amplifying the signals. However, this convergence comes at a cost to visual acuity (or Image resolution) because the pooled information from multiple cells is less distinct than it would be if the visual system received information from each rod cell individually.\*\* The convergence of rod cells also tends to make peripheral vision very sensitive to movement, and is responsible for the phenomenon of an individual seeing something vague occur out of the corner of his or her eye.\*\* Bolding mine. I remembered something like this from school, but decided not to trust my memory.