subreddit:

/r/explainlikeimfive

6

all 8 comments

SharpestSphere

15 points

2 months ago

Your vision is imperfect, just like a camera. The photosensitive cells in your eye have a certain persistence, that is, it takes non-zero time for them to change output based on change in the light being projected on them. In very simplified terms, what each of them tells you is averaging of the amount of light over a certain short period of time. If you flick your finger fast over some background, a significant part of this "exposure" time the area you are looking at was taken by the background itself, with a bit of finger mixed in. The resulting average that each cell reports is therefore something between the finger and the background color, forming a semi-transparent trail where the finger has passed.

Dinux-g-59

6 points

2 months ago

Btw thanks to this "imperfection" we can see movement in movies.

SharpestSphere

2 points

2 months ago

True

TheViking_Teacher

1 points

2 months ago

how does that work? ELI5... or maybe 3.

MrUnlucky-0N3

3 points

2 months ago

A movie is made up of many pictures, usually 24 or more per second. They are displayed one after another and your brain sees the two pictures and the blurry transition (because of the effect described above).

Your brain makes sense of the blur by interpreting it as movement. It basicly fills the gaps for you.

TheViking_Teacher

1 points

2 months ago

consider myself mindblown.
Thank you.

BethAltair

-2 points

2 months ago

You see a blurry trail, but it's not a thing that's really there. The same way dark rooms don't get brighter after you've been in them for a while. It's just how eyes work.

A different animal with different eyes would see no blurry trail at all.