This concept of attention can be better understood if we consider the internal base ear and its external base sound. Even though the sound of the ticking of a clock impinges on your ear drums while you are in your room, auditory consciousness with regard to that clock will not arise and you will not hear it unless you pay attention to it. The coming together of the internal base, the corresponding external base in the presence of that particular consciousness is called 'contact' a very important concept in Buddhism. There are six kinds of consciousness, namely visual consciousness, auditory consciousness etc. Feelings are of three kinds, pleasant, unpleasant and neutral arising due to contact through any one of the six sense doors.
Perception is similarly of six kinds.
Mental factors are of 50 different kinds, and consciousness takes any one of six different forms depending on the type of contact. When these five factors act together as a psycho-physical machine it gives to the unthinking man the idea of a self, but a close examination of how feelings, perception, mental factors, and consciousness, arise and disappear will reveal that the idea of a self is illusionary. There is no thinker behind a thought. It is just the thought that arose due to conditions and will cease with the ending of those conditions. For a better understanding that will reveal the absence of a Soul or self, one has to read the original texts available in translations.