Psychologists distinguish between two ways of processing sensory stimuli:

• Bottom-up processing. Receptors register information about the external environment and send it up to the brain for analysis and interpretation. Bottom-up processing is initiated by stimulus input.
• Top-down processing. Instead of starting with a stimulus, as bottom-up processing does, top-down processing starts with cognitive processing at the higher levels of the brain. These cognitive processes include knowledge, beliefs, and expectations.

When Stevie Wonder's hands touch the keys of a piano and he hears a sound come from the pressure he places on the keys, bottom-up processing is taking place. When he listens to a recording of one of his songs and modifies it based on his past music experience, top-down processing is occurring.

Another example involving both bottom-up and top-down processing is putting together a jigsaw puzzle (Friedrich, 2001). If you don't have the puzzle's original box with a picture of the finished product, you have to look at the shapes and colors of the pieces to determine how they fit together. That is essentially bottom-up processing.

But if you have the picture on the box to go by, you can select a particular area to work on and choose pieces that fit into that area. For example, if you know that a castle is on the right side of the puzzle, you can start by picking out only those pieces that look like they are part of a castle. Your task of fitting the pieces together then becomes much easier-you have fewer pieces to work with and have a general idea of how they should look once they are put together. Your selection process, which is based on prior knowledge, is an example of top-down processing.

1		A logic test asks students to complete the following number sequence: 1, 5, 9, _. This behavior is an example of
			A)	an absolute threshold
			B)	top-down processing
			C)	bottom-up processing
			D)	subliminal processing