Watch the spinning disc and see things expand!
{ Sight }
When you use this hands-on exhibit…you’ll stare into a spinning disc, then quickly look at something else and notice a very strange effect.
Just as your eyes adjust from bright light to dim light when you walk into a dark cinema, your visual system also needs to adjust from watching fast motion to something more stationary.
If you stare into a large water fall in a garden, then look off to the side, you’ll probably notice surrounding bushes or rocks start to ‘wobble’ and ‘boil’. This is due to a motion after effect.
Is your world really in a spin?
A motion after effect makes things appear to ‘expand’ or twist, even though the things don’t actually change size or move.
The effect is caused by how cells represent motion in your brain, particularly in your visual cortex.
There is debate over whether the motion-sensitive cells in your brain become fatigued or not, but continuous motion in a certain direction leaves us with a bias in the other direction—an after effect.
Different cells in your visual cortex respond to movement in different directions, but the motion after effect works if you see movement in part of your visual field, rather than your whole visual field.
So when you are driving down the highway in your car, you see everything moving and you don’t get a motion after effect when the car stops.
When you’re riding in a train however, you only notice movement through a smaller window, while the carriage seats and walls seem to be still.
When your train stops, the station platform can sometimes appear to move backwards as the motion after effect in your brain continues while your motion cells are resetting.