Take apples as an example: When we think of apples, we think of e.g. a round shaped object that is red and is juicy.
But when we are not thinking about apples, we are either not aware we are unconsciously thinking about apples, or apples never get called up consciously (or for the materialists, there are no neutral states that corresponds to the state of thinking about apples)
Whenever we try to consciously not thinking about apples, we often start with thinking what attributes an apple have and avoiding those attributes, thus in the process we end up conceiving the concept of an apple anyway (this is what the meme known as The Game based on)
So is it possible to consciously not thinking about apples, and if so, what does that mental or emotional state felt like. Any literature topic that investigate these kinds of antithinking?