How we change what others think, feel, believe and do
Eye Fills In Line
When the eye looks at several separate lines in proximity, it tries to join them up together so they form a single line or shape.
It does this most easily with straight lines and simple shapes. It helps if the parts of the bigger line are closer together and lined up.
We look at the items below and fill in the line gaps so we can see a line, a triangle and another wavy line.
In practice, the eye does not fill in the line, though it can be helpful to think of it this way. Of course it's the brain which does the processing. The eye simply reports hue and luminance.
This filling-in is part of a broader principle whereby the brain takes partial information and helpfully guesses what should be there. Indeed, it is so good at this you may not notice it happening. For example given the partial information of a passing, blur of a face you may think you have seen a friend, though stopping to say hello leads only to embarrassment.
The desperate filling in and seeking patterns that the brain does is partly done to help and partly to avoid the discomfort of uncertainty. Paradoxically, when this filling-in is inaccurate, it can cause even more confusion, yet we still prefer short-term confidence and willingly gain this in exchange for the occasional discomfort of being undeniably wrong.
When you are creating graphics or photographs, you can force the eye to follow even a partial line, especially if there are enough clues on how the parts of line join up. This helps you keep the original simple.
Also, when working on images, take care to watch for accidental lines of objects that will guide the eye in directions that you did not plan.