The sensory world constantly bombards the brain with more information than can be fully processed. Attention is the set of mechanisms that select some inputs for preferential handling while filtering others. It can be directed voluntarily toward a goal or captured automatically by sudden or salient events.

Networks spanning frontal and parietal cortex, along with subcortical structures such as the thalamus and superior colliculus, implement these selections. Attention enhances neural responses to attended stimuli, improves perceptual acuity, and facilitates encoding into memory. When attention fails, as in neglect syndromes or certain developmental disorders, entire regions of space or features of objects can go unnoticed.

Sustained attention over long periods draws on arousal systems involving norepinephrine and acetylcholine. Divided attention, by contrast, reveals the limits of processing capacity. Studying attention has practical value for education, interface design, and the treatment of attentional disorders.

Even simple laboratory tasks of detecting a target among distractors continue to reveal new principles of selection.