1) Attention refers to the ability to focus on a task and concentrate. There are different aspects of attention including selective attention, divided attention, and automatic vs controlled processing.
2) Selective attention is the ability to attend to one task over another. Divided attention is difficult as it is hard to attend to more than one thing at a time. Automatic processes like reading do not require attention while controlled processes do.
3) Sensation is the passive process of bringing information from the senses to the brain. Perception is the active process of selecting, organizing, and interpreting sensory information. Gestalt principles of grouping help in perceptual organization.