Our eyes are continuously bombarded by visual information - millions of colours, shapes and ever-changing motion - yet seeing never feels like work.

Researchers have discovered one reason: Our brains perform automatic visual smoothing over time. A new study has found that our visual perception of things is influenced by what we saw up to 15 seconds ago. This helps create a stable environment, despite sacrificing some accuracy.

It also means that what you see around you - that cup of coffee, the face of your co-worker, your computer screen - may be a time-averaged composite of now and the past.

"What you are seeing at the present moment is not a fresh snapshot of the world but rather an average of what you've seen in the past 10 to 15 seconds," said study author Jason Fischer, a neuroscientist at the Massachusetts Institute of Technology.

He showed subjects an image of a black-and-white grating tilted at a random angle for half a second, then asked them to identify the orientation of the grating they just saw. Then a few seconds later, another grating popped up, and they were to identify its angle.