Selective attention is a cognitive brain mechanism that enables one to process relevant inputs, thoughts, or actions while ignoring others that are less important, irrelevant or distracting. Arousal is a global state of the brain reflecting an overall level of responsiveness. We need attention because we can"t pay attention to everything at the same time. Bottlenecks embody how it is impossible to process everything at once. Bottle necks can be sensory, cognitive or motor. Sensory input is processed cognitively and then is carried out by motor system. Attention plays a role in the following: vision, audition/touch/smell, across modalities, thoughts, motor tasks. Invalid cue: square appears on opposite side as the target (longer. Overt shifts of attention: a shift of attention accompanied by corresponding movements of the eyes. Covert shifts of attention: a shift of attention in the absence of corresponding movements of the eyes: ex. we shift attention to the next word, before seeing the next word.