In mentalism we separate the concept of the senses from the concept of the sense-organs. The two are not the same. The senses must be mentally active before they can be active at all. Although the physical sense-organs are the usual condition for this activity, they are not the indispensable condition. The phenomena of dreams, hypnotism, and somnambulism demonstrate this adequately. The physical sense-organs do not operate, and cannot operate, unless the consciousness takes them into its purview. Absent-mindedness is a common example of what happens when it does not do this. There are even commoner examples, however, of which we never think at all until our attention is drawn to them. A man sitting at his desk will not be aware for long periods of time of the sense of touch or pressure where his body makes contact with his chair; the nerve endings in his skin may report the contact but the mind does not take it in, and consequently is not aware of it. The sense impressions of touch are simply not there at all.
-- Notebooks Category 21: Mentalism > Chapter 1: The Sensed World > # 30