Selective attention is the focussing of our attention on one stimulus to the exclusion of all others. Our brains will tend to focus on stimuli that we believe is most important at that time. For example, have you ever been on the phone and watching TV at the same time? Sometimes we will focus on what the person on the phone is saying. At other times, we may tune in more to what is on the television.
It is also true that we are constantly receiving and recording stimuli of which we are consciously unaware. At a party, you might be involved in a conversation with a friend, and not hear what is being said by others nearby, yet if one of them mentions your name, you will probably notice it immediately. Even if we wanted to attend to all stimuli, we could not.
We receive so many different stimuli at any one moment that we would simply be overwhelmed by them if we consciously registered them all. We would not be able to function if we were aware of all the stimuli registered by our five physical senses and internal stimuli, such as thoughts, feelings, values, impressions and so on.
Your nervous system continues to register peripheral stimuli without you being consciously aware of it. These stimuli are received from the fringe of our awareness. The latter example shows that the process of selection is largely controlled by the level of pertinence or relevance which stimuli hold for us. Some people are not interested to know what other people say about them, or more likely, their attention is on other matters, so they may not hear their name being mentioned.
In general, though in competition for our awareness, some stimuli and events have advantage over others because of their degree of relevance, or due to such factors such as surprise or intensity.
During ordinary waking consciousness, therefore, the individual tends to experience both active and passive consciousness.
****Passive consciousness receives incoming stimuli but does not actively process or consciously register them.
****Active consciousness engages us in conscious mental processes such as planning, analysing, and following our goals and intentions. It seems reasonable to postulate a continuum between consciousness and unconsciousness, according to which there are degrees of consciousness, though there is no real consensus on where one ends.