Acts of attention direct the limited neurological resources of humans to a number of stimuli, thoughts, and behaviors at any one time. Humans cannot process every stimulus that reaches the senses simultaneously, nor can they think about a great number of different problems and interests at the same time. Attention is not a single thing, for the brain has a large number of attentional processes, each performing specific tasks. In the past decade, the greatest body of work has concerned attentional selection in the visual system.