HM 4-4

1. HM 4-4 • Top-down processing essentially refers to the effect that meaning, familiarity, or context has in determining our perceptions (Goldstein, 2002). • Several examples of top-down processing can be presented fairly easily in class. Reversible figures can provide a good example of top-down processing if you generate and expectation in students before you show the figures.

2. HM 4-4 • For example, make copies of HM 4-3 and give a third of your class the top picture (rat), a third of your class the bottom picture (man), and a third of your class no picture. • Then, show the entire class TM 4-4 and ask them to record what they saw. • The third of the class who saw no prior picture will serve as you “control group” to determine what portion of students see the TM as a rat or a man.

3. HM 4-4 • The third who previously saw the rat picture should be more likely to perceive the TM as a rat; those who saw the man’s picture should be more likely to perceive the TM as a man. • Thus, students are likely to perceive what they have been lead to expect and to have a difficult time in reversing the figure.

4. HM 4-4 • Biederman (1981) described research that provides another good example of top-down processing. • Participants were asked to look at a particular location on a screen where a picture was to be flashed and to identify the object that appeared at that location. • Biederman found that people were less accurate when the object was shown in an unusual or atypical position (for example, a fire hydrant placed on top of a mailbox). • Participants’ knowledge about the objects affected their perception of those objects.

5. HM 4-4 • Although the pervious examples of top-down processing have shown examples of bias in perception, top-down processing can also occur in ways that are beneficial to us. • To demonstrate this effect, prepare copies of HM 4-4 for your students. Give each student a copy and ask them to attempt to decode the “meaningless” sentences. • Most students should do fairly well at this task because of their prior knowledge about how words and sentences are composed.

6. HM 4-4 • Thus, prior knowledge drives their performance on this task – top-down processing. • If you have international students for who English is a second language, they may perform more poorly at this task because their- expectations would not be as strong as native English speakers.

7. HM 4-4 • HM 4-4 answers: • MARY HAD A LITTLE LAMB HER FLEECE WAS WHITE AS SNOW. • THE SUN IS NOT SHINING TODAY. • SOME WORDS ARE EASIER TO UNDERSTAND THAN OTHERS.

8. HM 4-4 • Bottom-up processing assumes that our perceptions are built on the component parts of the object or scene that is presented to us. • As the text points out, the discovery of physiological cells that function as feature detectors supports the notion of bottom-up processing. • An example that you can use to illustrate bottom-up processing in class is provided on TM 4-5 (the word WIN).

9. HM 4-4 • The stimulus is composed of elements that stimulate various types of receptor cells and receptive fields. • These messages must then be brought together and integrated in order for perception to occur (another example is the cow transparency provided in the Wadsworth generic transparency set). • Students may note that bottom-up processing seems more difficult, but remind them of the difficulty they had during the top-down demonstrations.

10. HM 4-4 • In is hard to make the reversible figures reverse when you have been primed to expect one image.