It is a technique that enables you to distinguish the different ways that someone codes their thinking. For instance, for a moment think of someone you really like, get a picture of him or her and notice where that picture is located in your visual field (i.e. up and to the right or straight in front). Now clear the screen and do the same for someone you really dislike or like least. Are the two pictures located in different places? If they are then you just used contrastive analysis to determine how you code like and dislike of people you know.
To find out more about this, read: Using Your Brain For A Change – Bandler.