They do something called hesychasm. They do not believe in using your imagination or reasoning in prayer. They empty their mind and repeat the Jesus prayer while concentrating on their heart and His divine presense within them. From my little bit of study on mental prayer it seems that they are trying to force contemplation. Generally in the west the saints have said to begin mental prayer by using the imagination and reasoning and speaking with God. Gradually with spiritual progress in your prayer life you end up having less and less need for as much reasoning and imagination and most of the time is spent just speaking to God from the heart. You go from what's called discursive prayer to affective prayer. Basically as time goes on your prayer becomes more and more simple until God brings you to contemplation. Before contemplation you did most of the work with much effort. Now God begins to take a much more active role, infusing you with knowledge and love of Him. My point is that only God can bring you into contemplation when He wants to. It seems like in the east hesychasm is trying to skip straight to contemplation even though this is only done when God decides to. Of course God could work with this but it's different. It seems like the east and western approach to prayer begin differently but intend to lead to the same place, contemplation and union.