Concentration on a task.

Attention is concentration, or perceptive awareness, focused on a stimulus, such as a book or worksheet. During such periods of attention, the individual focuses on the stimuli of the task and ignores other environmental stimuli. There are distinct and measurable neurological and physiological aspects of attention, and the ability to achieve a state of attention may be limited by mental or physical dysfunctions. In fact, even short-term illnesses such as the flu can adversely affect the individual's ability to concentrate.

Psychologists use the term "attention span" to refer to the number of separate stimulus elements, or the amount of stimulus, that can be perceived and remembered after a brief presentation. Popularly, "attention span" is used to mean the amount of time that can be continuously spent in a state of attention.

Attention is directed toward a stimulus for any one of a number of...