There are two basic types of attention: focused attention and divided attention. Focused attention is the state of concentrating on one stimulus to the exclusion of all others. The purpose of focused attention is to actively focus on one thing without being distracted by other stimuli. This state can be physically and mentally tiring. Most behaviors are a combination of focused attention and divided attention.
Daily life is full of distractions and people are bombarded with all kinds of stimuli throughout a typical day. If a person noticed all of these stimuli, she would soon be overloaded and quite probably, completely ineffective at completing any task. Because of this, people exercise their focused, or selective, attention and filter out most of the information while retaining only that small fraction which they wish to concentrate on.
The human mind selects that small fraction in two ways. The first is a 'bottoms-up' approach where attention is stimulus-driven. This means there are certain aspects of a stimulus that attract a person's attention whether she wants them to or not. The second way is called 'top-down' processing which is goal-driven; the individual controls which stimuli receives attention. This is also referred to as executive attention.
One hierarchic model is based on the recovering of attention processes of brain damaged patients after a coma. It outlines five different attention activities in increasing level of difficulty that the patients could manage as their recovery process advanced. The first, and therefore, easiest for these patients was focused attention which was defined as the discrete response to specific sensory stimuli. Then came sustained attention, or vigilance, selective attention, alternating attention and finally divided attention. Divided attention was considered the most difficult as it refers to the ability to respond to multi-tasking and this could only be carried out by brain damaged patients nearing full recovery.
Paying attention is considered one of the keys to success as is focusing the mind on one task and filtering out all other distractions. People with attention problems such as Attention Deficiency Hyperactivity Disorder are unable to filter out the distractions and focus on one thing. Researchers from the University College in London have found those who are easily distracted and demonstrate a lack of focused attention have, in certain parts of their brain, larger volumes of gray matter. They concluded with the hypothesis that this may demonstrate a mild developmental malfunction in a brain that has not matured as it should.