Fully Absorbed

And FINALLY;

on Page Eighty two, how to develop the Base of Neither Perception or Non-Perception.  Back to Gunaratna: 

The fourth and final immaterial jhana, the base of neither-perception-nor-non-perception, is reached through the same preliminary procedure. The meditator can also reflect upon the unsatisfactoriness of perception, thinking: "Perception is a disease, perception is a boil, perception is a dart... this is peaceful, this is sublime, that is to say, neither-perception-nor-non-perception" (M.ii,231). In this way he ends his attachment to the base of nothingness and strengthens his resolve to attain the next higher stage. He then adverts to the four mental aggregates that constitute the attainment of the base of nothingness — its feeling, perception, mental formations and consciousness — contemplating them as "peaceful, peaceful," reviewing that base and striking at it with applied and sustained thought. As he does so the hindrances are suppressed, the mind passes through access and enters the base of neither-perception-nor-non-perception.

This jhana receives its name because, on the one hand, it lacks gross perception with its function of clearly discerning objects, and thus cannot be said to have perception; on the other, it retains a very subtle perception, and thus cannot be said to be without perception. Because all the mental functions are here reduced to the finest and most subtle level, this jhana is also named the attainment with residual formations. At this level the mind has reached the highest possible development in the direction of pure serenity. It has attained the most intense degree of concentration, becoming so refined that consciousness can no longer be described in terms of existence or non-existence. Yet even this attainment, from the Buddhist point of view, is still a mundane state which must finally give way to insight that alone leads to true liberation.