What is the difference between the sensation and perception?

IN OUR EVERYDAY EXPERIENCES, sensation and perception blend into one con-
tinuous process. In this chapter, we slow down that process to study its parts.

We start with the sensory receptors and work up to higher levels of processing.
Psychologists refer to sensory analysis that starts at the entry level as bottom-up

processing. But our minds also interpret what our senses detect. We construct per-
ceptions drawing both on sensations coming bottom-up to the brain and on our ex-
perience and expectations, which psychologists call top-down processing. For

example, as our brain deciphers the information in FIGURE 6.1, bottom-up processing
enables our sensory systems to detect the lines, angles, and colors that form the

horses, rider, and surroundings. Using top-down processing we consider the paint-
ing’s title, notice the apprehensive expressions, and then direct our attention to as-
pects of the painting that will give those observations meaning.

Nature’s sensory gifts suit each recipient’s needs. They enable each organism to
obtain essential information. Consider:
• A frog, which feeds on flying insects, has eyes with receptor cells that fire only in
response to small, dark, moving objects. A frog could starve to death knee-deep in
motionless flies. But let one zoom by and the frog’s “bug detector” cells snap awake.
• A male silkworm moth has receptors so sensitive to the female sex-attractant
odor that a single female need release only a billionth of an ounce per second to
attract every male silkworm moth within a mile. That is why there continue to be
silkworms.