The Yellow lines are the same length. Click on the name at bottom of pictue for an explanation.
Simultaneous Contrast Illusion. The background is a
colour gradient and progresses from dark grey to light grey. The horizontal bar appears to progress from light grey to dark grey, but is in fact just one colour.
An optical illusion. The two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.
An optical illusion (also called a visual illusion) is one which shows images that differ from normal reality.
The information gathered by the eye is processed in the brain to give a perception. That is normal, but in these cases the appearance does not tally with a physical measurement of the stimulus source.
There are three main types of visual illusion:
- literal optical illusions that create images which are different from the objects that make them
- physiological illusions: they are the effects on the eyes and brain of over-stimulation of brightness, colour, size, position, tilt, movement
- cognitive illusions, the result of unconscious inferences (brain makes the wrong decision).