In answering these questions, it is helpful to take into account the criteria we have used to determine where something should fit on a mental map. The first of these criteria is observability. Let us use the example of hunger to discuss the characteristics of a physiological need. Aside from a growling stomach, or a noticeable emaciated appearance, hunger is virtually unobservable. The actual sensation of hunger is just that - a sensation that is not observable to the outside world. On this level, hunger seems to be an internal occurrence.
A second criterion is accessibility. The sensation of hunger is highly accessible. One knows when one is hungry; there are certain identifiable experiences that accompany this need. A hungry person can feel their empty stomach, can crave certain foods, or can perhaps feel the start of a low blood sugar headache.
So far it seems there is not a problem. Physiological needs seem to fit nicely at the experience corner of a mental map. However upon considering the next criteria, things get interesting. Expressability is another criterion, or measuring device, to help us decide where things fit on a mental map. The question is this: Is hunger expressible? When one is hungry, it is common for one to say, "I am hungry." What is really being expressed in this statement? "I am hungry" does nothing to express the actual sensations accompanying hunger. When our friend says, "I am hungry" we infer that she is feeling the hunger sensations that we feel when we are hungry. But we cannot actually know if she feels the same sensations as we do when hungry.
Perhaps what is actually being expressed is a desire to eat. This encompasses the next criteria - directionality. As we have discussed, beliefs and attitudes are characteristically directional; that is that they have an "aboutness" to them, and that they are focused toward something. The statement "I am hungry" seems to be more an expression of belief or desire. When one says, "I am hungry" are they actually saying, "I want to eat"?
This seems unlikely. When I express hunger, I am trying to convey my discomfort at being hungry; that is - I am trying to express the sensations that I am feeling at the moment. This also seems odd since it is impossible to describe the actual sensations. I cannot make anyone feel what I am feeling. However, I make the effort to tell the people around me what is going on inside of my stomach. This means that the sensations felt from physiological needs are not expressible, although one may try to express them.
What is interesting here is the actual belief that one is hungry. When ones expresses hunger (unless one is lying) one must first believe that they are hungry. This is an attitude that has directionality; it has a definite aboutness. This is where the distinction between mind and body becomes less clear. Where is the point at which one has a physiological need, and where is the point at which one believes that one is hungry? There is no way for me to know when the need becomes a belief and hence becomes a desire, since I cannot climb inside my head and search for the signs of this distinction.
In deciding where physiological needs fit on a mental map, there seems to be three separate things going on. First are the actual sensations felt when such a need arises. These sensations fit in the experience corner of the map. They are accessible, unobservable, and inexpressible. Secondly are the beliefs and desires that accompany the need. One believes that one is hungry (or thirsty, or tired, etc.) and this in turn produces the desire to fulfill this need. These beliefs and desires are situated in the attitude corner of the mental map. They have directionality. Third is the expression of the need, and the actual fulfilling of the need. These things are obviously actions. They are observable behavior, visible to the outside world.
There then seem to be many things going on in the case of physiological needs. Broken down into separate categories, each portion of the need fits on a different place on a mental map of the mind. This fits well. When I am hungry, I know that I am hungry, and that I want to eat. This common statement easily sums what has been discussed here: the need is known and is accompanied by a desire to fulfill this need.
See also DESIRE, EMOTION, SENSATION