Considering both lines, we find that both lines are of exactly the same size.

The lines on the left are of the same length. However if one were to look at these lines in a different context, like in the one defined on the right, the horizontal line on the bottom appears to be longer than the one on the top. However a copy of the horizontal lines on the left were the ones that were used to create the additional image.

This is known as the Muller Lyer illusion.

Systems that analyze patterns by analyzing the data or input information are called data-driven or bottom-up systems.

Those that start from overall expectations and work their way down are called conceptually-driven or top-down systems.

However in order to solve difficult problems efficiently while using contextual information it useful to use both bottom-up and top-down processing simultaneously.