Some people can see perfectly, but cannot recognize members of their family. This person has what"s called prosopagnosia, aka face blindness. this illustrates the difference between sensation and perception. Sensation is the ability to see in this case, but includes hearing, touching, tasting, and smelling. Perception is how we put the impulses received from our senses together so they make sense. Although a person may see perfectly, they cannot perceive or correctly process the impulses so that they make sense. Sensation is part of bottom-up processing where our senses send information to our brain. Perception is part of top-down processing where our brain assembles the info to make sense of the impulses being sent to it. Scientists estimate we observe 11,000,000 bits of info per second. But we weed out all but 40 bits. The ability to screen out sensory information and focus on only a small portion of it is called selective attention.