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# Eye Extrapolates Line

Explanations > Perception > Visual Perception > Eye Extrapolates Line

## Description

When an eye follows a line, when it gets to the end of the visible line, the eye tends to keep going, as if propelled by the line.

The eye will move further and faster in this 'momentum' effect when:

• The line it has been following is straight.
• The line it has been following is relatively long.
• There are no other distractions that will pull the eye in another direction.
• The background is darker.

If a pattern has been distinguished in the line being followed, the eye may look for a repetition of that pattern. This can include patterns of line breaking or repeating twists and turns.

## Example

A row of three stones will send the eye looking for a fourth and fifth stone.

A wavy line will encourage the eye to expect further wavy lines beyond that which can be currently seen.

A person standing behind a post is recognized as the viewer extrapolates missing lines in their face.

## Discussion

Newton's first law of mechanics is that 'a body in motion will continue in a straight line unless acted upon by an external force'. The same principle applies to the eye. It is as if it has momentum, like a stone slid out across a frozen lake.

This effect can happen at sharp corners, where the eye 'overshoots'. The eye may return to follow the edge, but effort is expended in turning such a sharp corner. In this way, complex shapes can be more exhausting than simple shapes.

When there is nothing after a line stops, this creates a tension, even for a short period before another line segments is picked up by the eye. In this way, dotted lines can be more tense than solid lines. Random breaks can be even more tense as this introduces uncertainty. It is something like a song that has pauses in it, so you are never quite sure if it has yet ended.

# So what?

When you create lines, even as the edge of something else, be aware of the effect on the eye in the effort expended and the tension created. This can be done deliberately, for example to cause more exhaustion and hence reduce doubt in what is being portrayed.

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