Studied as a process or as a state. Brain has limited capacity to process information. Observer must choose to become aware of that which is relevant. Requires considerable cortical effort and: considerable focusing in order to distinguish relevant input from irrelevant input. Active participation (requires concentration and viliange fatigue) we select the stimuli that impinge on our receptors that we wish to attend. Also called active attention distinguish what"s relevant and irrelevant: central executive (frontal lobe) determines what is relevant/stores in memory. When information matches what is relevant will be remembered (conscious of it) Ensures survival forces observer to become aware of potentially relevant input (especially auditory modality: intrude the consciousness signal change from the past (those are intense) We have a limited capacity to carry out cognitive tasks. This is because of limited resources (or capacity for processing). A central executive must determine how these resources will be divided. Requires effort, processing of one task affects performance on another.