Anyone familiar with this trick of the eyes?

[geordief]

I was looking through the car windscreen  today as  the rain came down (parked with the  wipers off)

 

Through the windscreen  I was looking at a roughly painted  white wall (a rendered finish  which appeared as a collection of small pebbles-I think it may be called "pebbledash,actually)

 

Anyway the visual effect was that ,as the rainwater ran down the 45° angled windscreen  the "pebbles" seemed to move up the wall in an odd kind of opposing direction.

 

Anyone noticed this ,or similar before?

[Peterkin]

It's quite common to conflate with forward motion of one object with the backward motion of another. Much like the landscape rushing backward alongside the a moving train. In this case, it's the lens that is moving downward, so what you see through the lens moves upward. 

[geordief]

33 minutes ago, Peterkin said:

It's quite common to conflate with forward motion of one object with the backward motion of another. Much like the landscape rushing backward alongside the a moving train. In this case, it's the lens that is moving downward, so what you see through the lens moves upward. 

Well that is what immediately came to my mind when I noticed  this.

 

It felt just like when you are in the train station  and there is a train alongside the one you are seated in 

 

Then you notice that the other train is moving,but there is no way of knowing  whether  it is really the train you are in that is moving or the train alongside (unless  your train accelerates strongly or jerkily enough for you to notice that and  so make a determination)

 

In the case of looking through the windscreen of the car with a stream of water (ie the rain) running downwards the effect was to make  an illusion of the scene the other  side of  the windscreen run upwards.

 

But I, as the viewer was motionless, so it was not quite the same scenario  as with the train -and also it was the first time I had ever noticed it.

Edited April 17, 2022 by geordief

[Peterkin]

1 hour ago, geordief said:

But I, as the viewer was motionless, so it was not quite the same scenario  as with the train -and also it was the first time I had ever noticed it.

Yes, there are not many situations wherein the viewer is motionless and the the screen is moving. That's the affect of the rain. An unmoving screen (the window) is covered by a moving sheet of water, which converts it it into a moving lens, even though it is motionless relative to the viewer. Funny things happen to vision when transparent objects are superimposed. 

[mistermack]