The mental modifications are fivefold and are painful or pleasurable. These are correct cognition, misconception, fantasy, sleep and memory. Correct cognition is based on direct perception, valid inference and verbal testimony. Misconception is illusory knowledge based upon what is other than itself. Fantasy, empty of substance, is engendered by words and concepts.
Sleep is the modification engendered by the abeyance and absence of mental contents.
Memory is the not letting go of an object or image of subjective experience. This is indeed firmly grounded when it is persistently exercised for a long time, without interruption, and with earnest, reverential attention and devotion. Another sort of contemplation comes through the previous practice, the cessation of all mental contents, residual potencies alone remaining. It is close at hand for those with vehement intensity. Or by devoted self-surrender to the Lord.